/*
 * Copyright (c) 1996, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.io;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.UndeclaredThrowableException;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.PermissionCollection;
import java.security.Permissions;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import jdk.internal.misc.Unsafe;
import jdk.internal.reflect.CallerSensitive;
import jdk.internal.reflect.Reflection;
import jdk.internal.reflect.ReflectionFactory;
import sun.reflect.misc.ReflectUtil;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.misc.JavaSecurityAccess;
import static java.io.ObjectStreamField.*;

Serialization's descriptor for classes.  It contains the name and
serialVersionUID of the class.  The ObjectStreamClass for a specific class
loaded in this Java VM can be found/created using the lookup method.
The algorithm to compute the SerialVersionUID is described in

    Object Serialization Specification, Section 4.6, Stream Unique Identifiers.
Author:
     Mike Warres,      Roger Riggs
See Also:
ObjectStreamField

 *     Object Serialization Specification, Section 4, Class Descriptors
Since:
  1.1/**
 * Serialization's descriptor for classes.  It contains the name and
 * serialVersionUID of the class.  The ObjectStreamClass for a specific class
 * loaded in this Java VM can be found/created using the lookup method.
 *
 * <p>The algorithm to compute the SerialVersionUID is described in
 * <a href="{@docRoot}/../specs/serialization/class.html#stream-unique-identifiers">
 *     Object Serialization Specification, Section 4.6, Stream Unique Identifiers</a>.
 *
 * @author      Mike Warres
 * @author      Roger Riggs
 * @see ObjectStreamField
 * @see <a href="{@docRoot}/../specs/serialization/class.html">
 *     Object Serialization Specification, Section 4, Class Descriptors</a>
 * @since   1.1
 */
public class ObjectStreamClass implements Serializable {

    
serialPersistentFields value indicating no serializable fields /** serialPersistentFields value indicating no serializable fields */
    public static final ObjectStreamField[] NO_FIELDS =
        new ObjectStreamField[0];

    private static final long serialVersionUID = -6120832682080437368L;
    private static final ObjectStreamField[] serialPersistentFields =
        NO_FIELDS;

    
reflection factory for obtaining serialization constructors /** reflection factory for obtaining serialization constructors */
    private static final ReflectionFactory reflFactory =
        AccessController.doPrivileged(
            new ReflectionFactory.GetReflectionFactoryAction());

    private static class Caches {
        
cache mapping local classes -> descriptors /** cache mapping local classes -> descriptors */
        static final ConcurrentMap<WeakClassKey,Reference<?>> localDescs =
            new ConcurrentHashMap<>();

        
cache mapping field group/local desc pairs -> field reflectors /** cache mapping field group/local desc pairs -> field reflectors */
        static final ConcurrentMap<FieldReflectorKey,Reference<?>> reflectors =
            new ConcurrentHashMap<>();

        
queue for WeakReferences to local classes /** queue for WeakReferences to local classes */
        private static final ReferenceQueue<Class<?>> localDescsQueue =
            new ReferenceQueue<>();
        
queue for WeakReferences to field reflectors keys /** queue for WeakReferences to field reflectors keys */
        private static final ReferenceQueue<Class<?>> reflectorsQueue =
            new ReferenceQueue<>();
    }

    
class associated with this descriptor (if any) /** class associated with this descriptor (if any) */
    private Class<?> cl;
    
name of class represented by this descriptor /** name of class represented by this descriptor */
    private String name;
    
serialVersionUID of represented class (null if not computed yet) /** serialVersionUID of represented class (null if not computed yet) */
    private volatile Long suid;

    
true if represents dynamic proxy class /** true if represents dynamic proxy class */
    private boolean isProxy;
    
true if represents enum type /** true if represents enum type */
    private boolean isEnum;
    
true if represented class implements Serializable /** true if represented class implements Serializable */
    private boolean serializable;
    
true if represented class implements Externalizable /** true if represented class implements Externalizable */
    private boolean externalizable;
    
true if desc has data written by class-defined writeObject method /** true if desc has data written by class-defined writeObject method */
    private boolean hasWriteObjectData;
    
true if desc has externalizable data written in block data format; this
must be true by default to accommodate ObjectInputStream subclasses which
override readClassDescriptor() to return class descriptors obtained from
ObjectStreamClass.lookup() (see 4461737)
/**
     * true if desc has externalizable data written in block data format; this
     * must be true by default to accommodate ObjectInputStream subclasses which
     * override readClassDescriptor() to return class descriptors obtained from
     * ObjectStreamClass.lookup() (see 4461737)
     */
    private boolean hasBlockExternalData = true;

    
Contains information about InvalidClassException instances to be thrown
when attempting operations on an invalid class. Note that instances of
this class are immutable and are potentially shared among
ObjectStreamClass instances.
/**
     * Contains information about InvalidClassException instances to be thrown
     * when attempting operations on an invalid class. Note that instances of
     * this class are immutable and are potentially shared among
     * ObjectStreamClass instances.
     */
    private static class ExceptionInfo {
        private final String className;
        private final String message;

        ExceptionInfo(String cn, String msg) {
            className = cn;
            message = msg;
        }

        
Returns (does not throw) an InvalidClassException instance created
from the information in this object, suitable for being thrown by
the caller.
/**
         * Returns (does not throw) an InvalidClassException instance created
         * from the information in this object, suitable for being thrown by
         * the caller.
         */
        InvalidClassException newInvalidClassException() {
            return new InvalidClassException(className, message);
        }
    }

    
exception (if any) thrown while attempting to resolve class /** exception (if any) thrown while attempting to resolve class */
    private ClassNotFoundException resolveEx;
    
exception (if any) to throw if non-enum deserialization attempted /** exception (if any) to throw if non-enum deserialization attempted */
    private ExceptionInfo deserializeEx;
    
exception (if any) to throw if non-enum serialization attempted /** exception (if any) to throw if non-enum serialization attempted */
    private ExceptionInfo serializeEx;
    
exception (if any) to throw if default serialization attempted /** exception (if any) to throw if default serialization attempted */
    private ExceptionInfo defaultSerializeEx;

    
serializable fields /** serializable fields */
    private ObjectStreamField[] fields;
    
aggregate marshalled size of primitive fields /** aggregate marshalled size of primitive fields */
    private int primDataSize;
    
number of non-primitive fields /** number of non-primitive fields */
    private int numObjFields;
    
reflector for setting/getting serializable field values /** reflector for setting/getting serializable field values */
    private FieldReflector fieldRefl;
    
data layout of serialized objects described by this class desc /** data layout of serialized objects described by this class desc */
    private volatile ClassDataSlot[] dataLayout;

    
serialization-appropriate constructor, or null if none /** serialization-appropriate constructor, or null if none */
    private Constructor<?> cons;
    
protection domains that need to be checked when calling the constructor /** protection domains that need to be checked when calling the constructor */
    private ProtectionDomain[] domains;

    
class-defined writeObject method, or null if none /** class-defined writeObject method, or null if none */
    private Method writeObjectMethod;
    
class-defined readObject method, or null if none /** class-defined readObject method, or null if none */
    private Method readObjectMethod;
    
class-defined readObjectNoData method, or null if none /** class-defined readObjectNoData method, or null if none */
    private Method readObjectNoDataMethod;
    
class-defined writeReplace method, or null if none /** class-defined writeReplace method, or null if none */
    private Method writeReplaceMethod;
    
class-defined readResolve method, or null if none /** class-defined readResolve method, or null if none */
    private Method readResolveMethod;

    
local class descriptor for represented class (may point to self) /** local class descriptor for represented class (may point to self) */
    private ObjectStreamClass localDesc;
    
superclass descriptor appearing in stream /** superclass descriptor appearing in stream */
    private ObjectStreamClass superDesc;

    
true if, and only if, the object has been correctly initialized /** true if, and only if, the object has been correctly initialized */
    private boolean initialized;

    
Initializes native code.
/**
     * Initializes native code.
     */
    private static native void initNative();
    static {
        initNative();
    }

    
Find the descriptor for a class that can be serialized.  Creates an
ObjectStreamClass instance if one does not exist yet for class. Null is
returned if the specified class does not implement java.io.Serializable
or java.io.Externalizable.
Params:
cl – class for which to get the descriptor
Returns:
 the class descriptor for the specified class/**
     * Find the descriptor for a class that can be serialized.  Creates an
     * ObjectStreamClass instance if one does not exist yet for class. Null is
     * returned if the specified class does not implement java.io.Serializable
     * or java.io.Externalizable.
     *
     * @param   cl class for which to get the descriptor
     * @return  the class descriptor for the specified class
     */
    public static ObjectStreamClass lookup(Class<?> cl) {
        return lookup(cl, false);
    }

    
Returns the descriptor for any class, regardless of whether it implements Serializable. 
Params:
cl – class for which to get the descriptor
Returns:
      the class descriptor for the specified class
Since:
1.6/**
     * Returns the descriptor for any class, regardless of whether it
     * implements {@link Serializable}.
     *
     * @param        cl class for which to get the descriptor
     * @return       the class descriptor for the specified class
     * @since 1.6
     */
    public static ObjectStreamClass lookupAny(Class<?> cl) {
        return lookup(cl, true);
    }

    
Returns the name of the class described by this descriptor. This method returns the name of the class in the format that is used by the Class.getName method. 
Returns:
a string representing the name of the class/**
     * Returns the name of the class described by this descriptor.
     * This method returns the name of the class in the format that
     * is used by the {@link Class#getName} method.
     *
     * @return a string representing the name of the class
     */
    public String getName() {
        return name;
    }

    
Return the serialVersionUID for this class.  The serialVersionUID
defines a set of classes all with the same name that have evolved from a
common root class and agree to be serialized and deserialized using a
common format.  NonSerializable classes have a serialVersionUID of 0L.
Returns:
 the SUID of the class described by this descriptor/**
     * Return the serialVersionUID for this class.  The serialVersionUID
     * defines a set of classes all with the same name that have evolved from a
     * common root class and agree to be serialized and deserialized using a
     * common format.  NonSerializable classes have a serialVersionUID of 0L.
     *
     * @return  the SUID of the class described by this descriptor
     */
    public long getSerialVersionUID() {
        // REMIND: synchronize instead of relying on volatile?
        if (suid == null) {
            suid = AccessController.doPrivileged(
                new PrivilegedAction<Long>() {
                    public Long run() {
                        return computeDefaultSUID(cl);
                    }
                }
            );
        }
        return suid.longValue();
    }

    
Return the class in the local VM that this version is mapped to.  Null
is returned if there is no corresponding local class.
Returns:
 the Class instance that this descriptor represents/**
     * Return the class in the local VM that this version is mapped to.  Null
     * is returned if there is no corresponding local class.
     *
     * @return  the <code>Class</code> instance that this descriptor represents
     */
    @CallerSensitive
    public Class<?> forClass() {
        if (cl == null) {
            return null;
        }
        requireInitialized();
        if (System.getSecurityManager() != null) {
            Class<?> caller = Reflection.getCallerClass();
            if (ReflectUtil.needsPackageAccessCheck(caller.getClassLoader(), cl.getClassLoader())) {
                ReflectUtil.checkPackageAccess(cl);
            }
        }
        return cl;
    }

    
Return an array of the fields of this serializable class.
Returns:
 an array containing an element for each persistent field of
         this class. Returns an array of length zero if there are no
         fields.
Since:
1.2/**
     * Return an array of the fields of this serializable class.
     *
     * @return  an array containing an element for each persistent field of
     *          this class. Returns an array of length zero if there are no
     *          fields.
     * @since 1.2
     */
    public ObjectStreamField[] getFields() {
        return getFields(true);
    }

    
Get the field of this class by name.
Params:
name – the name of the data field to look for
Returns:
 The ObjectStreamField object of the named field or null if
         there is no such named field./**
     * Get the field of this class by name.
     *
     * @param   name the name of the data field to look for
     * @return  The ObjectStreamField object of the named field or null if
     *          there is no such named field.
     */
    public ObjectStreamField getField(String name) {
        return getField(name, null);
    }

    
Return a string describing this ObjectStreamClass.
/**
     * Return a string describing this ObjectStreamClass.
     */
    public String toString() {
        return name + ": static final long serialVersionUID = " +
            getSerialVersionUID() + "L;";
    }

    
Looks up and returns class descriptor for given class, or null if class
is non-serializable and "all" is set to false.
Params:
cl – class to look up
all – if true, return descriptors for all classes; if false, only
         return descriptors for serializable classes/**
     * Looks up and returns class descriptor for given class, or null if class
     * is non-serializable and "all" is set to false.
     *
     * @param   cl class to look up
     * @param   all if true, return descriptors for all classes; if false, only
     *          return descriptors for serializable classes
     */
    static ObjectStreamClass lookup(Class<?> cl, boolean all) {
        if (!(all || Serializable.class.isAssignableFrom(cl))) {
            return null;
        }
        processQueue(Caches.localDescsQueue, Caches.localDescs);
        WeakClassKey key = new WeakClassKey(cl, Caches.localDescsQueue);
        Reference<?> ref = Caches.localDescs.get(key);
        Object entry = null;
        if (ref != null) {
            entry = ref.get();
        }
        EntryFuture future = null;
        if (entry == null) {
            EntryFuture newEntry = new EntryFuture();
            Reference<?> newRef = new SoftReference<>(newEntry);
            do {
                if (ref != null) {
                    Caches.localDescs.remove(key, ref);
                }
                ref = Caches.localDescs.putIfAbsent(key, newRef);
                if (ref != null) {
                    entry = ref.get();
                }
            } while (ref != null && entry == null);
            if (entry == null) {
                future = newEntry;
            }
        }

        if (entry instanceof ObjectStreamClass) {  // check common case first
            return (ObjectStreamClass) entry;
        }
        if (entry instanceof EntryFuture) {
            future = (EntryFuture) entry;
            if (future.getOwner() == Thread.currentThread()) {
                /*
                 * Handle nested call situation described by 4803747: waiting
                 * for future value to be set by a lookup() call further up the
                 * stack will result in deadlock, so calculate and set the
                 * future value here instead.
                 */
                entry = null;
            } else {
                entry = future.get();
            }
        }
        if (entry == null) {
            try {
                entry = new ObjectStreamClass(cl);
            } catch (Throwable th) {
                entry = th;
            }
            if (future.set(entry)) {
                Caches.localDescs.put(key, new SoftReference<>(entry));
            } else {
                // nested lookup call already set future
                entry = future.get();
            }
        }

        if (entry instanceof ObjectStreamClass) {
            return (ObjectStreamClass) entry;
        } else if (entry instanceof RuntimeException) {
            throw (RuntimeException) entry;
        } else if (entry instanceof Error) {
            throw (Error) entry;
        } else {
            throw new InternalError("unexpected entry: " + entry);
        }
    }

    
Placeholder used in class descriptor and field reflector lookup tables
for an entry in the process of being initialized.  (Internal) callers
which receive an EntryFuture belonging to another thread as the result
of a lookup should call the get() method of the EntryFuture; this will
return the actual entry once it is ready for use and has been set().  To
conserve objects, EntryFutures synchronize on themselves.
/**
     * Placeholder used in class descriptor and field reflector lookup tables
     * for an entry in the process of being initialized.  (Internal) callers
     * which receive an EntryFuture belonging to another thread as the result
     * of a lookup should call the get() method of the EntryFuture; this will
     * return the actual entry once it is ready for use and has been set().  To
     * conserve objects, EntryFutures synchronize on themselves.
     */
    private static class EntryFuture {

        private static final Object unset = new Object();
        private final Thread owner = Thread.currentThread();
        private Object entry = unset;

        
Attempts to set the value contained by this EntryFuture.  If the
EntryFuture's value has not been set already, then the value is
saved, any callers blocked in the get() method are notified, and
true is returned.  If the value has already been set, then no saving
or notification occurs, and false is returned.
/**
         * Attempts to set the value contained by this EntryFuture.  If the
         * EntryFuture's value has not been set already, then the value is
         * saved, any callers blocked in the get() method are notified, and
         * true is returned.  If the value has already been set, then no saving
         * or notification occurs, and false is returned.
         */
        synchronized boolean set(Object entry) {
            if (this.entry != unset) {
                return false;
            }
            this.entry = entry;
            notifyAll();
            return true;
        }

        
Returns the value contained by this EntryFuture, blocking if
necessary until a value is set.
/**
         * Returns the value contained by this EntryFuture, blocking if
         * necessary until a value is set.
         */
        synchronized Object get() {
            boolean interrupted = false;
            while (entry == unset) {
                try {
                    wait();
                } catch (InterruptedException ex) {
                    interrupted = true;
                }
            }
            if (interrupted) {
                AccessController.doPrivileged(
                    new PrivilegedAction<>() {
                        public Void run() {
                            Thread.currentThread().interrupt();
                            return null;
                        }
                    }
                );
            }
            return entry;
        }

        
Returns the thread that created this EntryFuture.
/**
         * Returns the thread that created this EntryFuture.
         */
        Thread getOwner() {
            return owner;
        }
    }

    
Creates local class descriptor representing given class.
/**
     * Creates local class descriptor representing given class.
     */
    private ObjectStreamClass(final Class<?> cl) {
        this.cl = cl;
        name = cl.getName();
        isProxy = Proxy.isProxyClass(cl);
        isEnum = Enum.class.isAssignableFrom(cl);
        serializable = Serializable.class.isAssignableFrom(cl);
        externalizable = Externalizable.class.isAssignableFrom(cl);

        Class<?> superCl = cl.getSuperclass();
        superDesc = (superCl != null) ? lookup(superCl, false) : null;
        localDesc = this;

        if (serializable) {
            AccessController.doPrivileged(new PrivilegedAction<>() {
                public Void run() {
                    if (isEnum) {
                        suid = Long.valueOf(0);
                        fields = NO_FIELDS;
                        return null;
                    }
                    if (cl.isArray()) {
                        fields = NO_FIELDS;
                        return null;
                    }

                    suid = getDeclaredSUID(cl);
                    try {
                        fields = getSerialFields(cl);
                        computeFieldOffsets();
                    } catch (InvalidClassException e) {
                        serializeEx = deserializeEx =
                            new ExceptionInfo(e.classname, e.getMessage());
                        fields = NO_FIELDS;
                    }

                    if (externalizable) {
                        cons = getExternalizableConstructor(cl);
                    } else {
                        cons = getSerializableConstructor(cl);
                        writeObjectMethod = getPrivateMethod(cl, "writeObject",
                            new Class<?>[] { ObjectOutputStream.class },
                            Void.TYPE);
                        readObjectMethod = getPrivateMethod(cl, "readObject",
                            new Class<?>[] { ObjectInputStream.class },
                            Void.TYPE);
                        readObjectNoDataMethod = getPrivateMethod(
                            cl, "readObjectNoData", null, Void.TYPE);
                        hasWriteObjectData = (writeObjectMethod != null);
                    }
                    domains = getProtectionDomains(cons, cl);
                    writeReplaceMethod = getInheritableMethod(
                        cl, "writeReplace", null, Object.class);
                    readResolveMethod = getInheritableMethod(
                        cl, "readResolve", null, Object.class);
                    return null;
                }
            });
        } else {
            suid = Long.valueOf(0);
            fields = NO_FIELDS;
        }

        try {
            fieldRefl = getReflector(fields, this);
        } catch (InvalidClassException ex) {
            // field mismatches impossible when matching local fields vs. self
            throw new InternalError(ex);
        }

        if (deserializeEx == null) {
            if (isEnum) {
                deserializeEx = new ExceptionInfo(name, "enum type");
            } else if (cons == null) {
                deserializeEx = new ExceptionInfo(name, "no valid constructor");
            }
        }
        for (int i = 0; i < fields.length; i++) {
            if (fields[i].getField() == null) {
                defaultSerializeEx = new ExceptionInfo(
                    name, "unmatched serializable field(s) declared");
            }
        }
        initialized = true;
    }

    
Creates blank class descriptor which should be initialized via a
subsequent call to initProxy(), initNonProxy() or readNonProxy().
/**
     * Creates blank class descriptor which should be initialized via a
     * subsequent call to initProxy(), initNonProxy() or readNonProxy().
     */
    ObjectStreamClass() {
    }

    
Creates a PermissionDomain that grants no permission.
/**
     * Creates a PermissionDomain that grants no permission.
     */
    private ProtectionDomain noPermissionsDomain() {
        PermissionCollection perms = new Permissions();
        perms.setReadOnly();
        return new ProtectionDomain(null, perms);
    }

    
Aggregate the ProtectionDomains of all the classes that separate a concrete class cl from its ancestor's class declaring a constructor cons. If cl is defined by the boot loader, or the constructor cons is declared by cl, or if there is no security manager, then this method does nothing and null is returned. 
Params:
cons – A constructor declared by cl or one of its ancestors.
cl – A concrete class, which is either the class declaring the constructor cons, or a serializable subclass of that class.
Returns:
An array of ProtectionDomain representing the set of ProtectionDomain that separate the concrete class cl from its ancestor's declaring cons, or null./**
     * Aggregate the ProtectionDomains of all the classes that separate
     * a concrete class {@code cl} from its ancestor's class declaring
     * a constructor {@code cons}.
     *
     * If {@code cl} is defined by the boot loader, or the constructor
     * {@code cons} is declared by {@code cl}, or if there is no security
     * manager, then this method does nothing and {@code null} is returned.
     *
     * @param cons A constructor declared by {@code cl} or one of its
     *             ancestors.
     * @param cl A concrete class, which is either the class declaring
     *           the constructor {@code cons}, or a serializable subclass
     *           of that class.
     * @return An array of ProtectionDomain representing the set of
     *         ProtectionDomain that separate the concrete class {@code cl}
     *         from its ancestor's declaring {@code cons}, or {@code null}.
     */
    private ProtectionDomain[] getProtectionDomains(Constructor<?> cons,
                                                    Class<?> cl) {
        ProtectionDomain[] domains = null;
        if (cons != null && cl.getClassLoader() != null
                && System.getSecurityManager() != null) {
            Class<?> cls = cl;
            Class<?> fnscl = cons.getDeclaringClass();
            Set<ProtectionDomain> pds = null;
            while (cls != fnscl) {
                ProtectionDomain pd = cls.getProtectionDomain();
                if (pd != null) {
                    if (pds == null) pds = new HashSet<>();
                    pds.add(pd);
                }
                cls = cls.getSuperclass();
                if (cls == null) {
                    // that's not supposed to happen
                    // make a ProtectionDomain with no permission.
                    // should we throw instead?
                    if (pds == null) pds = new HashSet<>();
                    else pds.clear();
                    pds.add(noPermissionsDomain());
                    break;
                }
            }
            if (pds != null) {
                domains = pds.toArray(new ProtectionDomain[0]);
            }
        }
        return domains;
    }

    
Initializes class descriptor representing a proxy class.
/**
     * Initializes class descriptor representing a proxy class.
     */
    void initProxy(Class<?> cl,
                   ClassNotFoundException resolveEx,
                   ObjectStreamClass superDesc)
        throws InvalidClassException
    {
        ObjectStreamClass osc = null;
        if (cl != null) {
            osc = lookup(cl, true);
            if (!osc.isProxy) {
                throw new InvalidClassException(
                    "cannot bind proxy descriptor to a non-proxy class");
            }
        }
        this.cl = cl;
        this.resolveEx = resolveEx;
        this.superDesc = superDesc;
        isProxy = true;
        serializable = true;
        suid = Long.valueOf(0);
        fields = NO_FIELDS;
        if (osc != null) {
            localDesc = osc;
            name = localDesc.name;
            externalizable = localDesc.externalizable;
            writeReplaceMethod = localDesc.writeReplaceMethod;
            readResolveMethod = localDesc.readResolveMethod;
            deserializeEx = localDesc.deserializeEx;
            domains = localDesc.domains;
            cons = localDesc.cons;
        }
        fieldRefl = getReflector(fields, localDesc);
        initialized = true;
    }

    
Initializes class descriptor representing a non-proxy class.
/**
     * Initializes class descriptor representing a non-proxy class.
     */
    void initNonProxy(ObjectStreamClass model,
                      Class<?> cl,
                      ClassNotFoundException resolveEx,
                      ObjectStreamClass superDesc)
        throws InvalidClassException
    {
        long suid = Long.valueOf(model.getSerialVersionUID());
        ObjectStreamClass osc = null;
        if (cl != null) {
            osc = lookup(cl, true);
            if (osc.isProxy) {
                throw new InvalidClassException(
                        "cannot bind non-proxy descriptor to a proxy class");
            }
            if (model.isEnum != osc.isEnum) {
                throw new InvalidClassException(model.isEnum ?
                        "cannot bind enum descriptor to a non-enum class" :
                        "cannot bind non-enum descriptor to an enum class");
            }

            if (model.serializable == osc.serializable &&
                    !cl.isArray() &&
                    suid != osc.getSerialVersionUID()) {
                throw new InvalidClassException(osc.name,
                        "local class incompatible: " +
                                "stream classdesc serialVersionUID = " + suid +
                                ", local class serialVersionUID = " +
                                osc.getSerialVersionUID());
            }

            if (!classNamesEqual(model.name, osc.name)) {
                throw new InvalidClassException(osc.name,
                        "local class name incompatible with stream class " +
                                "name \"" + model.name + "\"");
            }

            if (!model.isEnum) {
                if ((model.serializable == osc.serializable) &&
                        (model.externalizable != osc.externalizable)) {
                    throw new InvalidClassException(osc.name,
                            "Serializable incompatible with Externalizable");
                }

                if ((model.serializable != osc.serializable) ||
                        (model.externalizable != osc.externalizable) ||
                        !(model.serializable || model.externalizable)) {
                    deserializeEx = new ExceptionInfo(
                            osc.name, "class invalid for deserialization");
                }
            }
        }

        this.cl = cl;
        this.resolveEx = resolveEx;
        this.superDesc = superDesc;
        name = model.name;
        this.suid = suid;
        isProxy = false;
        isEnum = model.isEnum;
        serializable = model.serializable;
        externalizable = model.externalizable;
        hasBlockExternalData = model.hasBlockExternalData;
        hasWriteObjectData = model.hasWriteObjectData;
        fields = model.fields;
        primDataSize = model.primDataSize;
        numObjFields = model.numObjFields;

        if (osc != null) {
            localDesc = osc;
            writeObjectMethod = localDesc.writeObjectMethod;
            readObjectMethod = localDesc.readObjectMethod;
            readObjectNoDataMethod = localDesc.readObjectNoDataMethod;
            writeReplaceMethod = localDesc.writeReplaceMethod;
            readResolveMethod = localDesc.readResolveMethod;
            if (deserializeEx == null) {
                deserializeEx = localDesc.deserializeEx;
            }
            domains = localDesc.domains;
            cons = localDesc.cons;
        }

        fieldRefl = getReflector(fields, localDesc);
        // reassign to matched fields so as to reflect local unshared settings
        fields = fieldRefl.getFields();
        initialized = true;
    }

    
Reads non-proxy class descriptor information from given input stream.
The resulting class descriptor is not fully functional; it can only be
used as input to the ObjectInputStream.resolveClass() and
ObjectStreamClass.initNonProxy() methods.
/**
     * Reads non-proxy class descriptor information from given input stream.
     * The resulting class descriptor is not fully functional; it can only be
     * used as input to the ObjectInputStream.resolveClass() and
     * ObjectStreamClass.initNonProxy() methods.
     */
    void readNonProxy(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        name = in.readUTF();
        suid = Long.valueOf(in.readLong());
        isProxy = false;

        byte flags = in.readByte();
        hasWriteObjectData =
            ((flags & ObjectStreamConstants.SC_WRITE_METHOD) != 0);
        hasBlockExternalData =
            ((flags & ObjectStreamConstants.SC_BLOCK_DATA) != 0);
        externalizable =
            ((flags & ObjectStreamConstants.SC_EXTERNALIZABLE) != 0);
        boolean sflag =
            ((flags & ObjectStreamConstants.SC_SERIALIZABLE) != 0);
        if (externalizable && sflag) {
            throw new InvalidClassException(
                name, "serializable and externalizable flags conflict");
        }
        serializable = externalizable || sflag;
        isEnum = ((flags & ObjectStreamConstants.SC_ENUM) != 0);
        if (isEnum && suid.longValue() != 0L) {
            throw new InvalidClassException(name,
                "enum descriptor has non-zero serialVersionUID: " + suid);
        }

        int numFields = in.readShort();
        if (isEnum && numFields != 0) {
            throw new InvalidClassException(name,
                "enum descriptor has non-zero field count: " + numFields);
        }
        fields = (numFields > 0) ?
            new ObjectStreamField[numFields] : NO_FIELDS;
        for (int i = 0; i < numFields; i++) {
            char tcode = (char) in.readByte();
            String fname = in.readUTF();
            String signature = ((tcode == 'L') || (tcode == '[')) ?
                in.readTypeString() : new String(new char[] { tcode });
            try {
                fields[i] = new ObjectStreamField(fname, signature, false);
            } catch (RuntimeException e) {
                throw (IOException) new InvalidClassException(name,
                    "invalid descriptor for field " + fname).initCause(e);
            }
        }
        computeFieldOffsets();
    }

    
Writes non-proxy class descriptor information to given output stream.
/**
     * Writes non-proxy class descriptor information to given output stream.
     */
    void writeNonProxy(ObjectOutputStream out) throws IOException {
        out.writeUTF(name);
        out.writeLong(getSerialVersionUID());

        byte flags = 0;
        if (externalizable) {
            flags |= ObjectStreamConstants.SC_EXTERNALIZABLE;
            int protocol = out.getProtocolVersion();
            if (protocol != ObjectStreamConstants.PROTOCOL_VERSION_1) {
                flags |= ObjectStreamConstants.SC_BLOCK_DATA;
            }
        } else if (serializable) {
            flags |= ObjectStreamConstants.SC_SERIALIZABLE;
        }
        if (hasWriteObjectData) {
            flags |= ObjectStreamConstants.SC_WRITE_METHOD;
        }
        if (isEnum) {
            flags |= ObjectStreamConstants.SC_ENUM;
        }
        out.writeByte(flags);

        out.writeShort(fields.length);
        for (int i = 0; i < fields.length; i++) {
            ObjectStreamField f = fields[i];
            out.writeByte(f.getTypeCode());
            out.writeUTF(f.getName());
            if (!f.isPrimitive()) {
                out.writeTypeString(f.getTypeString());
            }
        }
    }

    
Returns ClassNotFoundException (if any) thrown while attempting to
resolve local class corresponding to this class descriptor.
/**
     * Returns ClassNotFoundException (if any) thrown while attempting to
     * resolve local class corresponding to this class descriptor.
     */
    ClassNotFoundException getResolveException() {
        return resolveEx;
    }

    
Throws InternalError if not initialized.
/**
     * Throws InternalError if not initialized.
     */
    private final void requireInitialized() {
        if (!initialized)
            throw new InternalError("Unexpected call when not initialized");
    }

    
Throws InvalidClassException if not initialized.
To be called in cases where an uninitialized class descriptor indicates
a problem in the serialization stream.
/**
     * Throws InvalidClassException if not initialized.
     * To be called in cases where an uninitialized class descriptor indicates
     * a problem in the serialization stream.
     */
    final void checkInitialized() throws InvalidClassException {
        if (!initialized) {
            throw new InvalidClassException("Class descriptor should be initialized");
        }
    }

    
Throws an InvalidClassException if object instances referencing this
class descriptor should not be allowed to deserialize.  This method does
not apply to deserialization of enum constants.
/**
     * Throws an InvalidClassException if object instances referencing this
     * class descriptor should not be allowed to deserialize.  This method does
     * not apply to deserialization of enum constants.
     */
    void checkDeserialize() throws InvalidClassException {
        requireInitialized();
        if (deserializeEx != null) {
            throw deserializeEx.newInvalidClassException();
        }
    }

    
Throws an InvalidClassException if objects whose class is represented by
this descriptor should not be allowed to serialize.  This method does
not apply to serialization of enum constants.
/**
     * Throws an InvalidClassException if objects whose class is represented by
     * this descriptor should not be allowed to serialize.  This method does
     * not apply to serialization of enum constants.
     */
    void checkSerialize() throws InvalidClassException {
        requireInitialized();
        if (serializeEx != null) {
            throw serializeEx.newInvalidClassException();
        }
    }

    
Throws an InvalidClassException if objects whose class is represented by
this descriptor should not be permitted to use default serialization
(e.g., if the class declares serializable fields that do not correspond
to actual fields, and hence must use the GetField API).  This method
does not apply to deserialization of enum constants.
/**
     * Throws an InvalidClassException if objects whose class is represented by
     * this descriptor should not be permitted to use default serialization
     * (e.g., if the class declares serializable fields that do not correspond
     * to actual fields, and hence must use the GetField API).  This method
     * does not apply to deserialization of enum constants.
     */
    void checkDefaultSerialize() throws InvalidClassException {
        requireInitialized();
        if (defaultSerializeEx != null) {
            throw defaultSerializeEx.newInvalidClassException();
        }
    }

    
Returns superclass descriptor.  Note that on the receiving side, the
superclass descriptor may be bound to a class that is not a superclass
of the subclass descriptor's bound class.
/**
     * Returns superclass descriptor.  Note that on the receiving side, the
     * superclass descriptor may be bound to a class that is not a superclass
     * of the subclass descriptor's bound class.
     */
    ObjectStreamClass getSuperDesc() {
        requireInitialized();
        return superDesc;
    }

    
Returns the "local" class descriptor for the class associated with this
class descriptor (i.e., the result of
ObjectStreamClass.lookup(this.forClass())) or null if there is no class
associated with this descriptor.
/**
     * Returns the "local" class descriptor for the class associated with this
     * class descriptor (i.e., the result of
     * ObjectStreamClass.lookup(this.forClass())) or null if there is no class
     * associated with this descriptor.
     */
    ObjectStreamClass getLocalDesc() {
        requireInitialized();
        return localDesc;
    }

    
Returns arrays of ObjectStreamFields representing the serializable
fields of the represented class.  If copy is true, a clone of this class
descriptor's field array is returned, otherwise the array itself is
returned.
/**
     * Returns arrays of ObjectStreamFields representing the serializable
     * fields of the represented class.  If copy is true, a clone of this class
     * descriptor's field array is returned, otherwise the array itself is
     * returned.
     */
    ObjectStreamField[] getFields(boolean copy) {
        return copy ? fields.clone() : fields;
    }

    
Looks up a serializable field of the represented class by name and type.
A specified type of null matches all types, Object.class matches all
non-primitive types, and any other non-null type matches assignable
types only.  Returns matching field, or null if no match found.
/**
     * Looks up a serializable field of the represented class by name and type.
     * A specified type of null matches all types, Object.class matches all
     * non-primitive types, and any other non-null type matches assignable
     * types only.  Returns matching field, or null if no match found.
     */
    ObjectStreamField getField(String name, Class<?> type) {
        for (int i = 0; i < fields.length; i++) {
            ObjectStreamField f = fields[i];
            if (f.getName().equals(name)) {
                if (type == null ||
                    (type == Object.class && !f.isPrimitive()))
                {
                    return f;
                }
                Class<?> ftype = f.getType();
                if (ftype != null && type.isAssignableFrom(ftype)) {
                    return f;
                }
            }
        }
        return null;
    }

    
Returns true if class descriptor represents a dynamic proxy class, false
otherwise.
/**
     * Returns true if class descriptor represents a dynamic proxy class, false
     * otherwise.
     */
    boolean isProxy() {
        requireInitialized();
        return isProxy;
    }

    
Returns true if class descriptor represents an enum type, false
otherwise.
/**
     * Returns true if class descriptor represents an enum type, false
     * otherwise.
     */
    boolean isEnum() {
        requireInitialized();
        return isEnum;
    }

    
Returns true if represented class implements Externalizable, false
otherwise.
/**
     * Returns true if represented class implements Externalizable, false
     * otherwise.
     */
    boolean isExternalizable() {
        requireInitialized();
        return externalizable;
    }

    
Returns true if represented class implements Serializable, false
otherwise.
/**
     * Returns true if represented class implements Serializable, false
     * otherwise.
     */
    boolean isSerializable() {
        requireInitialized();
        return serializable;
    }

    
Returns true if class descriptor represents externalizable class that
has written its data in 1.2 (block data) format, false otherwise.
/**
     * Returns true if class descriptor represents externalizable class that
     * has written its data in 1.2 (block data) format, false otherwise.
     */
    boolean hasBlockExternalData() {
        requireInitialized();
        return hasBlockExternalData;
    }

    
Returns true if class descriptor represents serializable (but not
externalizable) class which has written its data via a custom
writeObject() method, false otherwise.
/**
     * Returns true if class descriptor represents serializable (but not
     * externalizable) class which has written its data via a custom
     * writeObject() method, false otherwise.
     */
    boolean hasWriteObjectData() {
        requireInitialized();
        return hasWriteObjectData;
    }

    
Returns true if represented class is serializable/externalizable and can
be instantiated by the serialization runtime--i.e., if it is
externalizable and defines a public no-arg constructor, or if it is
non-externalizable and its first non-serializable superclass defines an
accessible no-arg constructor.  Otherwise, returns false.
/**
     * Returns true if represented class is serializable/externalizable and can
     * be instantiated by the serialization runtime--i.e., if it is
     * externalizable and defines a public no-arg constructor, or if it is
     * non-externalizable and its first non-serializable superclass defines an
     * accessible no-arg constructor.  Otherwise, returns false.
     */
    boolean isInstantiable() {
        requireInitialized();
        return (cons != null);
    }

    
Returns true if represented class is serializable (but not
externalizable) and defines a conformant writeObject method.  Otherwise,
returns false.
/**
     * Returns true if represented class is serializable (but not
     * externalizable) and defines a conformant writeObject method.  Otherwise,
     * returns false.
     */
    boolean hasWriteObjectMethod() {
        requireInitialized();
        return (writeObjectMethod != null);
    }

    
Returns true if represented class is serializable (but not
externalizable) and defines a conformant readObject method.  Otherwise,
returns false.
/**
     * Returns true if represented class is serializable (but not
     * externalizable) and defines a conformant readObject method.  Otherwise,
     * returns false.
     */
    boolean hasReadObjectMethod() {
        requireInitialized();
        return (readObjectMethod != null);
    }

    
Returns true if represented class is serializable (but not
externalizable) and defines a conformant readObjectNoData method.
Otherwise, returns false.
/**
     * Returns true if represented class is serializable (but not
     * externalizable) and defines a conformant readObjectNoData method.
     * Otherwise, returns false.
     */
    boolean hasReadObjectNoDataMethod() {
        requireInitialized();
        return (readObjectNoDataMethod != null);
    }

    
Returns true if represented class is serializable or externalizable and
defines a conformant writeReplace method.  Otherwise, returns false.
/**
     * Returns true if represented class is serializable or externalizable and
     * defines a conformant writeReplace method.  Otherwise, returns false.
     */
    boolean hasWriteReplaceMethod() {
        requireInitialized();
        return (writeReplaceMethod != null);
    }

    
Returns true if represented class is serializable or externalizable and
defines a conformant readResolve method.  Otherwise, returns false.
/**
     * Returns true if represented class is serializable or externalizable and
     * defines a conformant readResolve method.  Otherwise, returns false.
     */
    boolean hasReadResolveMethod() {
        requireInitialized();
        return (readResolveMethod != null);
    }

    
Creates a new instance of the represented class.  If the class is
externalizable, invokes its public no-arg constructor; otherwise, if the
class is serializable, invokes the no-arg constructor of the first
non-serializable superclass.  Throws UnsupportedOperationException if
this class descriptor is not associated with a class, if the associated
class is non-serializable or if the appropriate no-arg constructor is
inaccessible/unavailable.
/**
     * Creates a new instance of the represented class.  If the class is
     * externalizable, invokes its public no-arg constructor; otherwise, if the
     * class is serializable, invokes the no-arg constructor of the first
     * non-serializable superclass.  Throws UnsupportedOperationException if
     * this class descriptor is not associated with a class, if the associated
     * class is non-serializable or if the appropriate no-arg constructor is
     * inaccessible/unavailable.
     */
    Object newInstance()
        throws InstantiationException, InvocationTargetException,
               UnsupportedOperationException
    {
        requireInitialized();
        if (cons != null) {
            try {
                if (domains == null || domains.length == 0) {
                    return cons.newInstance();
                } else {
                    JavaSecurityAccess jsa = SharedSecrets.getJavaSecurityAccess();
                    PrivilegedAction<?> pea = () -> {
                        try {
                            return cons.newInstance();
                        } catch (InstantiationException
                                 | InvocationTargetException
                                 | IllegalAccessException x) {
                            throw new UndeclaredThrowableException(x);
                        }
                    }; // Can't use PrivilegedExceptionAction with jsa
                    try {
                        return jsa.doIntersectionPrivilege(pea,
                                   AccessController.getContext(),
                                   new AccessControlContext(domains));
                    } catch (UndeclaredThrowableException x) {
                        Throwable cause = x.getCause();
                        if (cause instanceof InstantiationException)
                            throw (InstantiationException) cause;
                        if (cause instanceof InvocationTargetException)
                            throw (InvocationTargetException) cause;
                        if (cause instanceof IllegalAccessException)
                            throw (IllegalAccessException) cause;
                        // not supposed to happen
                        throw x;
                    }
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            } catch (InstantiationError err) {
                var ex = new InstantiationException();
                ex.initCause(err);
                throw ex;
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Invokes the writeObject method of the represented serializable class.
Throws UnsupportedOperationException if this class descriptor is not
associated with a class, or if the class is externalizable,
non-serializable or does not define writeObject.
/**
     * Invokes the writeObject method of the represented serializable class.
     * Throws UnsupportedOperationException if this class descriptor is not
     * associated with a class, or if the class is externalizable,
     * non-serializable or does not define writeObject.
     */
    void invokeWriteObject(Object obj, ObjectOutputStream out)
        throws IOException, UnsupportedOperationException
    {
        requireInitialized();
        if (writeObjectMethod != null) {
            try {
                writeObjectMethod.invoke(obj, new Object[]{ out });
            } catch (InvocationTargetException ex) {
                Throwable th = ex.getTargetException();
                if (th instanceof IOException) {
                    throw (IOException) th;
                } else {
                    throwMiscException(th);
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Invokes the readObject method of the represented serializable class.
Throws UnsupportedOperationException if this class descriptor is not
associated with a class, or if the class is externalizable,
non-serializable or does not define readObject.
/**
     * Invokes the readObject method of the represented serializable class.
     * Throws UnsupportedOperationException if this class descriptor is not
     * associated with a class, or if the class is externalizable,
     * non-serializable or does not define readObject.
     */
    void invokeReadObject(Object obj, ObjectInputStream in)
        throws ClassNotFoundException, IOException,
               UnsupportedOperationException
    {
        requireInitialized();
        if (readObjectMethod != null) {
            try {
                readObjectMethod.invoke(obj, new Object[]{ in });
            } catch (InvocationTargetException ex) {
                Throwable th = ex.getTargetException();
                if (th instanceof ClassNotFoundException) {
                    throw (ClassNotFoundException) th;
                } else if (th instanceof IOException) {
                    throw (IOException) th;
                } else {
                    throwMiscException(th);
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Invokes the readObjectNoData method of the represented serializable
class.  Throws UnsupportedOperationException if this class descriptor is
not associated with a class, or if the class is externalizable,
non-serializable or does not define readObjectNoData.
/**
     * Invokes the readObjectNoData method of the represented serializable
     * class.  Throws UnsupportedOperationException if this class descriptor is
     * not associated with a class, or if the class is externalizable,
     * non-serializable or does not define readObjectNoData.
     */
    void invokeReadObjectNoData(Object obj)
        throws IOException, UnsupportedOperationException
    {
        requireInitialized();
        if (readObjectNoDataMethod != null) {
            try {
                readObjectNoDataMethod.invoke(obj, (Object[]) null);
            } catch (InvocationTargetException ex) {
                Throwable th = ex.getTargetException();
                if (th instanceof ObjectStreamException) {
                    throw (ObjectStreamException) th;
                } else {
                    throwMiscException(th);
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Invokes the writeReplace method of the represented serializable class and
returns the result.  Throws UnsupportedOperationException if this class
descriptor is not associated with a class, or if the class is
non-serializable or does not define writeReplace.
/**
     * Invokes the writeReplace method of the represented serializable class and
     * returns the result.  Throws UnsupportedOperationException if this class
     * descriptor is not associated with a class, or if the class is
     * non-serializable or does not define writeReplace.
     */
    Object invokeWriteReplace(Object obj)
        throws IOException, UnsupportedOperationException
    {
        requireInitialized();
        if (writeReplaceMethod != null) {
            try {
                return writeReplaceMethod.invoke(obj, (Object[]) null);
            } catch (InvocationTargetException ex) {
                Throwable th = ex.getTargetException();
                if (th instanceof ObjectStreamException) {
                    throw (ObjectStreamException) th;
                } else {
                    throwMiscException(th);
                    throw new InternalError(th);  // never reached
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Invokes the readResolve method of the represented serializable class and
returns the result.  Throws UnsupportedOperationException if this class
descriptor is not associated with a class, or if the class is
non-serializable or does not define readResolve.
/**
     * Invokes the readResolve method of the represented serializable class and
     * returns the result.  Throws UnsupportedOperationException if this class
     * descriptor is not associated with a class, or if the class is
     * non-serializable or does not define readResolve.
     */
    Object invokeReadResolve(Object obj)
        throws IOException, UnsupportedOperationException
    {
        requireInitialized();
        if (readResolveMethod != null) {
            try {
                return readResolveMethod.invoke(obj, (Object[]) null);
            } catch (InvocationTargetException ex) {
                Throwable th = ex.getTargetException();
                if (th instanceof ObjectStreamException) {
                    throw (ObjectStreamException) th;
                } else {
                    throwMiscException(th);
                    throw new InternalError(th);  // never reached
                }
            } catch (IllegalAccessException ex) {
                // should not occur, as access checks have been suppressed
                throw new InternalError(ex);
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }

    
Class representing the portion of an object's serialized form allotted
to data described by a given class descriptor.  If "hasData" is false,
the object's serialized form does not contain data associated with the
class descriptor.
/**
     * Class representing the portion of an object's serialized form allotted
     * to data described by a given class descriptor.  If "hasData" is false,
     * the object's serialized form does not contain data associated with the
     * class descriptor.
     */
    static class ClassDataSlot {

        
class descriptor "occupying" this slot /** class descriptor "occupying" this slot */
        final ObjectStreamClass desc;
        
true if serialized form includes data for this slot's descriptor /** true if serialized form includes data for this slot's descriptor */
        final boolean hasData;

        ClassDataSlot(ObjectStreamClass desc, boolean hasData) {
            this.desc = desc;
            this.hasData = hasData;
        }
    }

    
Returns array of ClassDataSlot instances representing the data layout
(including superclass data) for serialized objects described by this
class descriptor.  ClassDataSlots are ordered by inheritance with those
containing "higher" superclasses appearing first.  The final
ClassDataSlot contains a reference to this descriptor.
/**
     * Returns array of ClassDataSlot instances representing the data layout
     * (including superclass data) for serialized objects described by this
     * class descriptor.  ClassDataSlots are ordered by inheritance with those
     * containing "higher" superclasses appearing first.  The final
     * ClassDataSlot contains a reference to this descriptor.
     */
    ClassDataSlot[] getClassDataLayout() throws InvalidClassException {
        // REMIND: synchronize instead of relying on volatile?
        if (dataLayout == null) {
            dataLayout = getClassDataLayout0();
        }
        return dataLayout;
    }

    private ClassDataSlot[] getClassDataLayout0()
        throws InvalidClassException
    {
        ArrayList<ClassDataSlot> slots = new ArrayList<>();
        Class<?> start = cl, end = cl;

        // locate closest non-serializable superclass
        while (end != null && Serializable.class.isAssignableFrom(end)) {
            end = end.getSuperclass();
        }

        HashSet<String> oscNames = new HashSet<>(3);

        for (ObjectStreamClass d = this; d != null; d = d.superDesc) {
            if (oscNames.contains(d.name)) {
                throw new InvalidClassException("Circular reference.");
            } else {
                oscNames.add(d.name);
            }

            // search up inheritance hierarchy for class with matching name
            String searchName = (d.cl != null) ? d.cl.getName() : d.name;
            Class<?> match = null;
            for (Class<?> c = start; c != end; c = c.getSuperclass()) {
                if (searchName.equals(c.getName())) {
                    match = c;
                    break;
                }
            }

            // add "no data" slot for each unmatched class below match
            if (match != null) {
                for (Class<?> c = start; c != match; c = c.getSuperclass()) {
                    slots.add(new ClassDataSlot(
                        ObjectStreamClass.lookup(c, true), false));
                }
                start = match.getSuperclass();
            }

            // record descriptor/class pairing
            slots.add(new ClassDataSlot(d.getVariantFor(match), true));
        }

        // add "no data" slot for any leftover unmatched classes
        for (Class<?> c = start; c != end; c = c.getSuperclass()) {
            slots.add(new ClassDataSlot(
                ObjectStreamClass.lookup(c, true), false));
        }

        // order slots from superclass -> subclass
        Collections.reverse(slots);
        return slots.toArray(new ClassDataSlot[slots.size()]);
    }

    
Returns aggregate size (in bytes) of marshalled primitive field values
for represented class.
/**
     * Returns aggregate size (in bytes) of marshalled primitive field values
     * for represented class.
     */
    int getPrimDataSize() {
        return primDataSize;
    }

    
Returns number of non-primitive serializable fields of represented
class.
/**
     * Returns number of non-primitive serializable fields of represented
     * class.
     */
    int getNumObjFields() {
        return numObjFields;
    }

    
Fetches the serializable primitive field values of object obj and
marshals them into byte array buf starting at offset 0.  It is the
responsibility of the caller to ensure that obj is of the proper type if
non-null.
/**
     * Fetches the serializable primitive field values of object obj and
     * marshals them into byte array buf starting at offset 0.  It is the
     * responsibility of the caller to ensure that obj is of the proper type if
     * non-null.
     */
    void getPrimFieldValues(Object obj, byte[] buf) {
        fieldRefl.getPrimFieldValues(obj, buf);
    }

    
Sets the serializable primitive fields of object obj using values
unmarshalled from byte array buf starting at offset 0.  It is the
responsibility of the caller to ensure that obj is of the proper type if
non-null.
/**
     * Sets the serializable primitive fields of object obj using values
     * unmarshalled from byte array buf starting at offset 0.  It is the
     * responsibility of the caller to ensure that obj is of the proper type if
     * non-null.
     */
    void setPrimFieldValues(Object obj, byte[] buf) {
        fieldRefl.setPrimFieldValues(obj, buf);
    }

    
Fetches the serializable object field values of object obj and stores
them in array vals starting at offset 0.  It is the responsibility of
the caller to ensure that obj is of the proper type if non-null.
/**
     * Fetches the serializable object field values of object obj and stores
     * them in array vals starting at offset 0.  It is the responsibility of
     * the caller to ensure that obj is of the proper type if non-null.
     */
    void getObjFieldValues(Object obj, Object[] vals) {
        fieldRefl.getObjFieldValues(obj, vals);
    }

    
Checks that the given values, from array vals starting at offset 0,
are assignable to the given serializable object fields.
Throws:
ClassCastException – if any value is not assignable/**
     * Checks that the given values, from array vals starting at offset 0,
     * are assignable to the given serializable object fields.
     * @throws ClassCastException if any value is not assignable
     */
    void checkObjFieldValueTypes(Object obj, Object[] vals) {
        fieldRefl.checkObjectFieldValueTypes(obj, vals);
    }

    
Sets the serializable object fields of object obj using values from
array vals starting at offset 0.  It is the responsibility of the caller
to ensure that obj is of the proper type if non-null.
/**
     * Sets the serializable object fields of object obj using values from
     * array vals starting at offset 0.  It is the responsibility of the caller
     * to ensure that obj is of the proper type if non-null.
     */
    void setObjFieldValues(Object obj, Object[] vals) {
        fieldRefl.setObjFieldValues(obj, vals);
    }

    
Calculates and sets serializable field offsets, as well as primitive
data size and object field count totals.  Throws InvalidClassException
if fields are illegally ordered.
/**
     * Calculates and sets serializable field offsets, as well as primitive
     * data size and object field count totals.  Throws InvalidClassException
     * if fields are illegally ordered.
     */
    private void computeFieldOffsets() throws InvalidClassException {
        primDataSize = 0;
        numObjFields = 0;
        int firstObjIndex = -1;

        for (int i = 0; i < fields.length; i++) {
            ObjectStreamField f = fields[i];
            switch (f.getTypeCode()) {
                case 'Z':
                case 'B':
                    f.setOffset(primDataSize++);
                    break;

                case 'C':
                case 'S':
                    f.setOffset(primDataSize);
                    primDataSize += 2;
                    break;

                case 'I':
                case 'F':
                    f.setOffset(primDataSize);
                    primDataSize += 4;
                    break;

                case 'J':
                case 'D':
                    f.setOffset(primDataSize);
                    primDataSize += 8;
                    break;

                case '[':
                case 'L':
                    f.setOffset(numObjFields++);
                    if (firstObjIndex == -1) {
                        firstObjIndex = i;
                    }
                    break;

                default:
                    throw new InternalError();
            }
        }
        if (firstObjIndex != -1 &&
            firstObjIndex + numObjFields != fields.length)
        {
            throw new InvalidClassException(name, "illegal field order");
        }
    }

    
If given class is the same as the class associated with this class
descriptor, returns reference to this class descriptor.  Otherwise,
returns variant of this class descriptor bound to given class.
/**
     * If given class is the same as the class associated with this class
     * descriptor, returns reference to this class descriptor.  Otherwise,
     * returns variant of this class descriptor bound to given class.
     */
    private ObjectStreamClass getVariantFor(Class<?> cl)
        throws InvalidClassException
    {
        if (this.cl == cl) {
            return this;
        }
        ObjectStreamClass desc = new ObjectStreamClass();
        if (isProxy) {
            desc.initProxy(cl, null, superDesc);
        } else {
            desc.initNonProxy(this, cl, null, superDesc);
        }
        return desc;
    }

    
Returns public no-arg constructor of given class, or null if none found.
Access checks are disabled on the returned constructor (if any), since
the defining class may still be non-public.
/**
     * Returns public no-arg constructor of given class, or null if none found.
     * Access checks are disabled on the returned constructor (if any), since
     * the defining class may still be non-public.
     */
    private static Constructor<?> getExternalizableConstructor(Class<?> cl) {
        try {
            Constructor<?> cons = cl.getDeclaredConstructor((Class<?>[]) null);
            cons.setAccessible(true);
            return ((cons.getModifiers() & Modifier.PUBLIC) != 0) ?
                cons : null;
        } catch (NoSuchMethodException ex) {
            return null;
        }
    }

    
Returns subclass-accessible no-arg constructor of first non-serializable
superclass, or null if none found.  Access checks are disabled on the
returned constructor (if any).
/**
     * Returns subclass-accessible no-arg constructor of first non-serializable
     * superclass, or null if none found.  Access checks are disabled on the
     * returned constructor (if any).
     */
    private static Constructor<?> getSerializableConstructor(Class<?> cl) {
        return reflFactory.newConstructorForSerialization(cl);
    }

    
Returns non-static, non-abstract method with given signature provided it
is defined by or accessible (via inheritance) by the given class, or
null if no match found.  Access checks are disabled on the returned
method (if any).
/**
     * Returns non-static, non-abstract method with given signature provided it
     * is defined by or accessible (via inheritance) by the given class, or
     * null if no match found.  Access checks are disabled on the returned
     * method (if any).
     */
    private static Method getInheritableMethod(Class<?> cl, String name,
                                               Class<?>[] argTypes,
                                               Class<?> returnType)
    {
        Method meth = null;
        Class<?> defCl = cl;
        while (defCl != null) {
            try {
                meth = defCl.getDeclaredMethod(name, argTypes);
                break;
            } catch (NoSuchMethodException ex) {
                defCl = defCl.getSuperclass();
            }
        }

        if ((meth == null) || (meth.getReturnType() != returnType)) {
            return null;
        }
        meth.setAccessible(true);
        int mods = meth.getModifiers();
        if ((mods & (Modifier.STATIC | Modifier.ABSTRACT)) != 0) {
            return null;
        } else if ((mods & (Modifier.PUBLIC | Modifier.PROTECTED)) != 0) {
            return meth;
        } else if ((mods & Modifier.PRIVATE) != 0) {
            return (cl == defCl) ? meth : null;
        } else {
            return packageEquals(cl, defCl) ? meth : null;
        }
    }

    
Returns non-static private method with given signature defined by given
class, or null if none found.  Access checks are disabled on the
returned method (if any).
/**
     * Returns non-static private method with given signature defined by given
     * class, or null if none found.  Access checks are disabled on the
     * returned method (if any).
     */
    private static Method getPrivateMethod(Class<?> cl, String name,
                                           Class<?>[] argTypes,
                                           Class<?> returnType)
    {
        try {
            Method meth = cl.getDeclaredMethod(name, argTypes);
            meth.setAccessible(true);
            int mods = meth.getModifiers();
            return ((meth.getReturnType() == returnType) &&
                    ((mods & Modifier.STATIC) == 0) &&
                    ((mods & Modifier.PRIVATE) != 0)) ? meth : null;
        } catch (NoSuchMethodException ex) {
            return null;
        }
    }

    
Returns true if classes are defined in the same runtime package, false
otherwise.
/**
     * Returns true if classes are defined in the same runtime package, false
     * otherwise.
     */
    private static boolean packageEquals(Class<?> cl1, Class<?> cl2) {
        return (cl1.getClassLoader() == cl2.getClassLoader() &&
                cl1.getPackageName().equals(cl2.getPackageName()));
    }

    
Compares class names for equality, ignoring package names.  Returns true
if class names equal, false otherwise.
/**
     * Compares class names for equality, ignoring package names.  Returns true
     * if class names equal, false otherwise.
     */
    private static boolean classNamesEqual(String name1, String name2) {
        int idx1 = name1.lastIndexOf('.') + 1;
        int idx2 = name2.lastIndexOf('.') + 1;
        int len1 = name1.length() - idx1;
        int len2 = name2.length() - idx2;
        return len1 == len2 &&
                name1.regionMatches(idx1, name2, idx2, len1);
    }

    
Returns JVM type signature for given list of parameters and return type.
/**
     * Returns JVM type signature for given list of parameters and return type.
     */
    private static String getMethodSignature(Class<?>[] paramTypes,
                                             Class<?> retType)
    {
        StringBuilder sb = new StringBuilder();
        sb.append('(');
        for (int i = 0; i < paramTypes.length; i++) {
            appendClassSignature(sb, paramTypes[i]);
        }
        sb.append(')');
        appendClassSignature(sb, retType);
        return sb.toString();
    }

    
Convenience method for throwing an exception that is either a
RuntimeException, Error, or of some unexpected type (in which case it is
wrapped inside an IOException).
/**
     * Convenience method for throwing an exception that is either a
     * RuntimeException, Error, or of some unexpected type (in which case it is
     * wrapped inside an IOException).
     */
    private static void throwMiscException(Throwable th) throws IOException {
        if (th instanceof RuntimeException) {
            throw (RuntimeException) th;
        } else if (th instanceof Error) {
            throw (Error) th;
        } else {
            IOException ex = new IOException("unexpected exception type");
            ex.initCause(th);
            throw ex;
        }
    }

    
Returns ObjectStreamField array describing the serializable fields of
the given class.  Serializable fields backed by an actual field of the
class are represented by ObjectStreamFields with corresponding non-null
Field objects.  Throws InvalidClassException if the (explicitly
declared) serializable fields are invalid.
/**
     * Returns ObjectStreamField array describing the serializable fields of
     * the given class.  Serializable fields backed by an actual field of the
     * class are represented by ObjectStreamFields with corresponding non-null
     * Field objects.  Throws InvalidClassException if the (explicitly
     * declared) serializable fields are invalid.
     */
    private static ObjectStreamField[] getSerialFields(Class<?> cl)
        throws InvalidClassException
    {
        ObjectStreamField[] fields;
        if (Serializable.class.isAssignableFrom(cl) &&
            !Externalizable.class.isAssignableFrom(cl) &&
            !Proxy.isProxyClass(cl) &&
            !cl.isInterface())
        {
            if ((fields = getDeclaredSerialFields(cl)) == null) {
                fields = getDefaultSerialFields(cl);
            }
            Arrays.sort(fields);
        } else {
            fields = NO_FIELDS;
        }
        return fields;
    }

    
Returns serializable fields of given class as defined explicitly by a
"serialPersistentFields" field, or null if no appropriate
"serialPersistentFields" field is defined.  Serializable fields backed
by an actual field of the class are represented by ObjectStreamFields
with corresponding non-null Field objects.  For compatibility with past
releases, a "serialPersistentFields" field with a null value is
considered equivalent to not declaring "serialPersistentFields".  Throws
InvalidClassException if the declared serializable fields are
invalid--e.g., if multiple fields share the same name.
/**
     * Returns serializable fields of given class as defined explicitly by a
     * "serialPersistentFields" field, or null if no appropriate
     * "serialPersistentFields" field is defined.  Serializable fields backed
     * by an actual field of the class are represented by ObjectStreamFields
     * with corresponding non-null Field objects.  For compatibility with past
     * releases, a "serialPersistentFields" field with a null value is
     * considered equivalent to not declaring "serialPersistentFields".  Throws
     * InvalidClassException if the declared serializable fields are
     * invalid--e.g., if multiple fields share the same name.
     */
    private static ObjectStreamField[] getDeclaredSerialFields(Class<?> cl)
        throws InvalidClassException
    {
        ObjectStreamField[] serialPersistentFields = null;
        try {
            Field f = cl.getDeclaredField("serialPersistentFields");
            int mask = Modifier.PRIVATE | Modifier.STATIC | Modifier.FINAL;
            if ((f.getModifiers() & mask) == mask) {
                f.setAccessible(true);
                serialPersistentFields = (ObjectStreamField[]) f.get(null);
            }
        } catch (Exception ex) {
        }
        if (serialPersistentFields == null) {
            return null;
        } else if (serialPersistentFields.length == 0) {
            return NO_FIELDS;
        }

        ObjectStreamField[] boundFields =
            new ObjectStreamField[serialPersistentFields.length];
        Set<String> fieldNames = new HashSet<>(serialPersistentFields.length);

        for (int i = 0; i < serialPersistentFields.length; i++) {
            ObjectStreamField spf = serialPersistentFields[i];

            String fname = spf.getName();
            if (fieldNames.contains(fname)) {
                throw new InvalidClassException(
                    "multiple serializable fields named " + fname);
            }
            fieldNames.add(fname);

            try {
                Field f = cl.getDeclaredField(fname);
                if ((f.getType() == spf.getType()) &&
                    ((f.getModifiers() & Modifier.STATIC) == 0))
                {
                    boundFields[i] =
                        new ObjectStreamField(f, spf.isUnshared(), true);
                }
            } catch (NoSuchFieldException ex) {
            }
            if (boundFields[i] == null) {
                boundFields[i] = new ObjectStreamField(
                    fname, spf.getType(), spf.isUnshared());
            }
        }
        return boundFields;
    }

    
Returns array of ObjectStreamFields corresponding to all non-static
non-transient fields declared by given class.  Each ObjectStreamField
contains a Field object for the field it represents.  If no default
serializable fields exist, NO_FIELDS is returned.
/**
     * Returns array of ObjectStreamFields corresponding to all non-static
     * non-transient fields declared by given class.  Each ObjectStreamField
     * contains a Field object for the field it represents.  If no default
     * serializable fields exist, NO_FIELDS is returned.
     */
    private static ObjectStreamField[] getDefaultSerialFields(Class<?> cl) {
        Field[] clFields = cl.getDeclaredFields();
        ArrayList<ObjectStreamField> list = new ArrayList<>();
        int mask = Modifier.STATIC | Modifier.TRANSIENT;

        for (int i = 0; i < clFields.length; i++) {
            if ((clFields[i].getModifiers() & mask) == 0) {
                list.add(new ObjectStreamField(clFields[i], false, true));
            }
        }
        int size = list.size();
        return (size == 0) ? NO_FIELDS :
            list.toArray(new ObjectStreamField[size]);
    }

    
Returns explicit serial version UID value declared by given class, or
null if none.
/**
     * Returns explicit serial version UID value declared by given class, or
     * null if none.
     */
    private static Long getDeclaredSUID(Class<?> cl) {
        try {
            Field f = cl.getDeclaredField("serialVersionUID");
            int mask = Modifier.STATIC | Modifier.FINAL;
            if ((f.getModifiers() & mask) == mask) {
                f.setAccessible(true);
                return Long.valueOf(f.getLong(null));
            }
        } catch (Exception ex) {
        }
        return null;
    }

    
Computes the default serial version UID value for the given class.
/**
     * Computes the default serial version UID value for the given class.
     */
    private static long computeDefaultSUID(Class<?> cl) {
        if (!Serializable.class.isAssignableFrom(cl) || Proxy.isProxyClass(cl))
        {
            return 0L;
        }

        try {
            ByteArrayOutputStream bout = new ByteArrayOutputStream();
            DataOutputStream dout = new DataOutputStream(bout);

            dout.writeUTF(cl.getName());

            int classMods = cl.getModifiers() &
                (Modifier.PUBLIC | Modifier.FINAL |
                 Modifier.INTERFACE | Modifier.ABSTRACT);

            /*
             * compensate for javac bug in which ABSTRACT bit was set for an
             * interface only if the interface declared methods
             */
            Method[] methods = cl.getDeclaredMethods();
            if ((classMods & Modifier.INTERFACE) != 0) {
                classMods = (methods.length > 0) ?
                    (classMods | Modifier.ABSTRACT) :
                    (classMods & ~Modifier.ABSTRACT);
            }
            dout.writeInt(classMods);

            if (!cl.isArray()) {
                /*
                 * compensate for change in 1.2FCS in which
                 * Class.getInterfaces() was modified to return Cloneable and
                 * Serializable for array classes.
                 */
                Class<?>[] interfaces = cl.getInterfaces();
                String[] ifaceNames = new String[interfaces.length];
                for (int i = 0; i < interfaces.length; i++) {
                    ifaceNames[i] = interfaces[i].getName();
                }
                Arrays.sort(ifaceNames);
                for (int i = 0; i < ifaceNames.length; i++) {
                    dout.writeUTF(ifaceNames[i]);
                }
            }

            Field[] fields = cl.getDeclaredFields();
            MemberSignature[] fieldSigs = new MemberSignature[fields.length];
            for (int i = 0; i < fields.length; i++) {
                fieldSigs[i] = new MemberSignature(fields[i]);
            }
            Arrays.sort(fieldSigs, new Comparator<>() {
                public int compare(MemberSignature ms1, MemberSignature ms2) {
                    return ms1.name.compareTo(ms2.name);
                }
            });
            for (int i = 0; i < fieldSigs.length; i++) {
                MemberSignature sig = fieldSigs[i];
                int mods = sig.member.getModifiers() &
                    (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                     Modifier.STATIC | Modifier.FINAL | Modifier.VOLATILE |
                     Modifier.TRANSIENT);
                if (((mods & Modifier.PRIVATE) == 0) ||
                    ((mods & (Modifier.STATIC | Modifier.TRANSIENT)) == 0))
                {
                    dout.writeUTF(sig.name);
                    dout.writeInt(mods);
                    dout.writeUTF(sig.signature);
                }
            }

            if (hasStaticInitializer(cl)) {
                dout.writeUTF("<clinit>");
                dout.writeInt(Modifier.STATIC);
                dout.writeUTF("()V");
            }

            Constructor<?>[] cons = cl.getDeclaredConstructors();
            MemberSignature[] consSigs = new MemberSignature[cons.length];
            for (int i = 0; i < cons.length; i++) {
                consSigs[i] = new MemberSignature(cons[i]);
            }
            Arrays.sort(consSigs, new Comparator<>() {
                public int compare(MemberSignature ms1, MemberSignature ms2) {
                    return ms1.signature.compareTo(ms2.signature);
                }
            });
            for (int i = 0; i < consSigs.length; i++) {
                MemberSignature sig = consSigs[i];
                int mods = sig.member.getModifiers() &
                    (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                     Modifier.STATIC | Modifier.FINAL |
                     Modifier.SYNCHRONIZED | Modifier.NATIVE |
                     Modifier.ABSTRACT | Modifier.STRICT);
                if ((mods & Modifier.PRIVATE) == 0) {
                    dout.writeUTF("<init>");
                    dout.writeInt(mods);
                    dout.writeUTF(sig.signature.replace('/', '.'));
                }
            }

            MemberSignature[] methSigs = new MemberSignature[methods.length];
            for (int i = 0; i < methods.length; i++) {
                methSigs[i] = new MemberSignature(methods[i]);
            }
            Arrays.sort(methSigs, new Comparator<>() {
                public int compare(MemberSignature ms1, MemberSignature ms2) {
                    int comp = ms1.name.compareTo(ms2.name);
                    if (comp == 0) {
                        comp = ms1.signature.compareTo(ms2.signature);
                    }
                    return comp;
                }
            });
            for (int i = 0; i < methSigs.length; i++) {
                MemberSignature sig = methSigs[i];
                int mods = sig.member.getModifiers() &
                    (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED |
                     Modifier.STATIC | Modifier.FINAL |
                     Modifier.SYNCHRONIZED | Modifier.NATIVE |
                     Modifier.ABSTRACT | Modifier.STRICT);
                if ((mods & Modifier.PRIVATE) == 0) {
                    dout.writeUTF(sig.name);
                    dout.writeInt(mods);
                    dout.writeUTF(sig.signature.replace('/', '.'));
                }
            }

            dout.flush();

            MessageDigest md = MessageDigest.getInstance("SHA");
            byte[] hashBytes = md.digest(bout.toByteArray());
            long hash = 0;
            for (int i = Math.min(hashBytes.length, 8) - 1; i >= 0; i--) {
                hash = (hash << 8) | (hashBytes[i] & 0xFF);
            }
            return hash;
        } catch (IOException ex) {
            throw new InternalError(ex);
        } catch (NoSuchAlgorithmException ex) {
            throw new SecurityException(ex.getMessage());
        }
    }

    
Returns true if the given class defines a static initializer method,
false otherwise.
/**
     * Returns true if the given class defines a static initializer method,
     * false otherwise.
     */
    private static native boolean hasStaticInitializer(Class<?> cl);

    
Class for computing and caching field/constructor/method signatures
during serialVersionUID calculation.
/**
     * Class for computing and caching field/constructor/method signatures
     * during serialVersionUID calculation.
     */
    private static class MemberSignature {

        public final Member member;
        public final String name;
        public final String signature;

        public MemberSignature(Field field) {
            member = field;
            name = field.getName();
            signature = getClassSignature(field.getType());
        }

        public MemberSignature(Constructor<?> cons) {
            member = cons;
            name = cons.getName();
            signature = getMethodSignature(
                cons.getParameterTypes(), Void.TYPE);
        }

        public MemberSignature(Method meth) {
            member = meth;
            name = meth.getName();
            signature = getMethodSignature(
                meth.getParameterTypes(), meth.getReturnType());
        }
    }

    
Class for setting and retrieving serializable field values in batch.
/**
     * Class for setting and retrieving serializable field values in batch.
     */
    // REMIND: dynamically generate these?
    private static class FieldReflector {

        
handle for performing unsafe operations /** handle for performing unsafe operations */
        private static final Unsafe unsafe = Unsafe.getUnsafe();

        
fields to operate on /** fields to operate on */
        private final ObjectStreamField[] fields;
        
number of primitive fields /** number of primitive fields */
        private final int numPrimFields;
        
unsafe field keys for reading fields - may contain dupes /** unsafe field keys for reading fields - may contain dupes */
        private final long[] readKeys;
        
unsafe fields keys for writing fields - no dupes /** unsafe fields keys for writing fields - no dupes */
        private final long[] writeKeys;
        
field data offsets /** field data offsets */
        private final int[] offsets;
        
field type codes /** field type codes */
        private final char[] typeCodes;
        
field types /** field types */
        private final Class<?>[] types;

        
Constructs FieldReflector capable of setting/getting values from the
subset of fields whose ObjectStreamFields contain non-null
reflective Field objects.  ObjectStreamFields with null Fields are
treated as filler, for which get operations return default values
and set operations discard given values.
/**
         * Constructs FieldReflector capable of setting/getting values from the
         * subset of fields whose ObjectStreamFields contain non-null
         * reflective Field objects.  ObjectStreamFields with null Fields are
         * treated as filler, for which get operations return default values
         * and set operations discard given values.
         */
        FieldReflector(ObjectStreamField[] fields) {
            this.fields = fields;
            int nfields = fields.length;
            readKeys = new long[nfields];
            writeKeys = new long[nfields];
            offsets = new int[nfields];
            typeCodes = new char[nfields];
            ArrayList<Class<?>> typeList = new ArrayList<>();
            Set<Long> usedKeys = new HashSet<>();


            for (int i = 0; i < nfields; i++) {
                ObjectStreamField f = fields[i];
                Field rf = f.getField();
                long key = (rf != null) ?
                    unsafe.objectFieldOffset(rf) : Unsafe.INVALID_FIELD_OFFSET;
                readKeys[i] = key;
                writeKeys[i] = usedKeys.add(key) ?
                    key : Unsafe.INVALID_FIELD_OFFSET;
                offsets[i] = f.getOffset();
                typeCodes[i] = f.getTypeCode();
                if (!f.isPrimitive()) {
                    typeList.add((rf != null) ? rf.getType() : null);
                }
            }

            types = typeList.toArray(new Class<?>[typeList.size()]);
            numPrimFields = nfields - types.length;
        }

        
Returns list of ObjectStreamFields representing fields operated on
by this reflector.  The shared/unshared values and Field objects
contained by ObjectStreamFields in the list reflect their bindings
to locally defined serializable fields.
/**
         * Returns list of ObjectStreamFields representing fields operated on
         * by this reflector.  The shared/unshared values and Field objects
         * contained by ObjectStreamFields in the list reflect their bindings
         * to locally defined serializable fields.
         */
        ObjectStreamField[] getFields() {
            return fields;
        }

        
Fetches the serializable primitive field values of object obj and
marshals them into byte array buf starting at offset 0.  The caller
is responsible for ensuring that obj is of the proper type.
/**
         * Fetches the serializable primitive field values of object obj and
         * marshals them into byte array buf starting at offset 0.  The caller
         * is responsible for ensuring that obj is of the proper type.
         */
        void getPrimFieldValues(Object obj, byte[] buf) {
            if (obj == null) {
                throw new NullPointerException();
            }
            /* assuming checkDefaultSerialize() has been called on the class
             * descriptor this FieldReflector was obtained from, no field keys
             * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.
             */
            for (int i = 0; i < numPrimFields; i++) {
                long key = readKeys[i];
                int off = offsets[i];
                switch (typeCodes[i]) {
                    case 'Z':
                        Bits.putBoolean(buf, off, unsafe.getBoolean(obj, key));
                        break;

                    case 'B':
                        buf[off] = unsafe.getByte(obj, key);
                        break;

                    case 'C':
                        Bits.putChar(buf, off, unsafe.getChar(obj, key));
                        break;

                    case 'S':
                        Bits.putShort(buf, off, unsafe.getShort(obj, key));
                        break;

                    case 'I':
                        Bits.putInt(buf, off, unsafe.getInt(obj, key));
                        break;

                    case 'F':
                        Bits.putFloat(buf, off, unsafe.getFloat(obj, key));
                        break;

                    case 'J':
                        Bits.putLong(buf, off, unsafe.getLong(obj, key));
                        break;

                    case 'D':
                        Bits.putDouble(buf, off, unsafe.getDouble(obj, key));
                        break;

                    default:
                        throw new InternalError();
                }
            }
        }

        
Sets the serializable primitive fields of object obj using values
unmarshalled from byte array buf starting at offset 0.  The caller
is responsible for ensuring that obj is of the proper type.
/**
         * Sets the serializable primitive fields of object obj using values
         * unmarshalled from byte array buf starting at offset 0.  The caller
         * is responsible for ensuring that obj is of the proper type.
         */
        void setPrimFieldValues(Object obj, byte[] buf) {
            if (obj == null) {
                throw new NullPointerException();
            }
            for (int i = 0; i < numPrimFields; i++) {
                long key = writeKeys[i];
                if (key == Unsafe.INVALID_FIELD_OFFSET) {
                    continue;           // discard value
                }
                int off = offsets[i];
                switch (typeCodes[i]) {
                    case 'Z':
                        unsafe.putBoolean(obj, key, Bits.getBoolean(buf, off));
                        break;

                    case 'B':
                        unsafe.putByte(obj, key, buf[off]);
                        break;

                    case 'C':
                        unsafe.putChar(obj, key, Bits.getChar(buf, off));
                        break;

                    case 'S':
                        unsafe.putShort(obj, key, Bits.getShort(buf, off));
                        break;

                    case 'I':
                        unsafe.putInt(obj, key, Bits.getInt(buf, off));
                        break;

                    case 'F':
                        unsafe.putFloat(obj, key, Bits.getFloat(buf, off));
                        break;

                    case 'J':
                        unsafe.putLong(obj, key, Bits.getLong(buf, off));
                        break;

                    case 'D':
                        unsafe.putDouble(obj, key, Bits.getDouble(buf, off));
                        break;

                    default:
                        throw new InternalError();
                }
            }
        }

        
Fetches the serializable object field values of object obj and
stores them in array vals starting at offset 0.  The caller is
responsible for ensuring that obj is of the proper type.
/**
         * Fetches the serializable object field values of object obj and
         * stores them in array vals starting at offset 0.  The caller is
         * responsible for ensuring that obj is of the proper type.
         */
        void getObjFieldValues(Object obj, Object[] vals) {
            if (obj == null) {
                throw new NullPointerException();
            }
            /* assuming checkDefaultSerialize() has been called on the class
             * descriptor this FieldReflector was obtained from, no field keys
             * in array should be equal to Unsafe.INVALID_FIELD_OFFSET.
             */
            for (int i = numPrimFields; i < fields.length; i++) {
                switch (typeCodes[i]) {
                    case 'L':
                    case '[':
                        vals[offsets[i]] = unsafe.getObject(obj, readKeys[i]);
                        break;

                    default:
                        throw new InternalError();
                }
            }
        }

        
Checks that the given values, from array vals starting at offset 0,
are assignable to the given serializable object fields.
Throws:
ClassCastException – if any value is not assignable/**
         * Checks that the given values, from array vals starting at offset 0,
         * are assignable to the given serializable object fields.
         * @throws ClassCastException if any value is not assignable
         */
        void checkObjectFieldValueTypes(Object obj, Object[] vals) {
            setObjFieldValues(obj, vals, true);
        }

        
Sets the serializable object fields of object obj using values from
array vals starting at offset 0.  The caller is responsible for
ensuring that obj is of the proper type; however, attempts to set a
field with a value of the wrong type will trigger an appropriate
ClassCastException.
/**
         * Sets the serializable object fields of object obj using values from
         * array vals starting at offset 0.  The caller is responsible for
         * ensuring that obj is of the proper type; however, attempts to set a
         * field with a value of the wrong type will trigger an appropriate
         * ClassCastException.
         */
        void setObjFieldValues(Object obj, Object[] vals) {
            setObjFieldValues(obj, vals, false);
        }

        private void setObjFieldValues(Object obj, Object[] vals, boolean dryRun) {
            if (obj == null) {
                throw new NullPointerException();
            }
            for (int i = numPrimFields; i < fields.length; i++) {
                long key = writeKeys[i];
                if (key == Unsafe.INVALID_FIELD_OFFSET) {
                    continue;           // discard value
                }
                switch (typeCodes[i]) {
                    case 'L':
                    case '[':
                        Object val = vals[offsets[i]];
                        if (val != null &&
                            !types[i - numPrimFields].isInstance(val))
                        {
                            Field f = fields[i].getField();
                            throw new ClassCastException(
                                "cannot assign instance of " +
                                val.getClass().getName() + " to field " +
                                f.getDeclaringClass().getName() + "." +
                                f.getName() + " of type " +
                                f.getType().getName() + " in instance of " +
                                obj.getClass().getName());
                        }
                        if (!dryRun)
                            unsafe.putObject(obj, key, val);
                        break;

                    default:
                        throw new InternalError();
                }
            }
        }
    }

    
Matches given set of serializable fields with serializable fields
described by the given local class descriptor, and returns a
FieldReflector instance capable of setting/getting values from the
subset of fields that match (non-matching fields are treated as filler,
for which get operations return default values and set operations
discard given values).  Throws InvalidClassException if unresolvable
type conflicts exist between the two sets of fields.
/**
     * Matches given set of serializable fields with serializable fields
     * described by the given local class descriptor, and returns a
     * FieldReflector instance capable of setting/getting values from the
     * subset of fields that match (non-matching fields are treated as filler,
     * for which get operations return default values and set operations
     * discard given values).  Throws InvalidClassException if unresolvable
     * type conflicts exist between the two sets of fields.
     */
    private static FieldReflector getReflector(ObjectStreamField[] fields,
                                               ObjectStreamClass localDesc)
        throws InvalidClassException
    {
        // class irrelevant if no fields
        Class<?> cl = (localDesc != null && fields.length > 0) ?
            localDesc.cl : null;
        processQueue(Caches.reflectorsQueue, Caches.reflectors);
        FieldReflectorKey key = new FieldReflectorKey(cl, fields,
                                                      Caches.reflectorsQueue);
        Reference<?> ref = Caches.reflectors.get(key);
        Object entry = null;
        if (ref != null) {
            entry = ref.get();
        }
        EntryFuture future = null;
        if (entry == null) {
            EntryFuture newEntry = new EntryFuture();
            Reference<?> newRef = new SoftReference<>(newEntry);
            do {
                if (ref != null) {
                    Caches.reflectors.remove(key, ref);
                }
                ref = Caches.reflectors.putIfAbsent(key, newRef);
                if (ref != null) {
                    entry = ref.get();
                }
            } while (ref != null && entry == null);
            if (entry == null) {
                future = newEntry;
            }
        }

        if (entry instanceof FieldReflector) {  // check common case first
            return (FieldReflector) entry;
        } else if (entry instanceof EntryFuture) {
            entry = ((EntryFuture) entry).get();
        } else if (entry == null) {
            try {
                entry = new FieldReflector(matchFields(fields, localDesc));
            } catch (Throwable th) {
                entry = th;
            }
            future.set(entry);
            Caches.reflectors.put(key, new SoftReference<>(entry));
        }

        if (entry instanceof FieldReflector) {
            return (FieldReflector) entry;
        } else if (entry instanceof InvalidClassException) {
            throw (InvalidClassException) entry;
        } else if (entry instanceof RuntimeException) {
            throw (RuntimeException) entry;
        } else if (entry instanceof Error) {
            throw (Error) entry;
        } else {
            throw new InternalError("unexpected entry: " + entry);
        }
    }

    
FieldReflector cache lookup key.  Keys are considered equal if they
refer to the same class and equivalent field formats.
/**
     * FieldReflector cache lookup key.  Keys are considered equal if they
     * refer to the same class and equivalent field formats.
     */
    private static class FieldReflectorKey extends WeakReference<Class<?>> {

        private final String[] sigs;
        private final int hash;
        private final boolean nullClass;

        FieldReflectorKey(Class<?> cl, ObjectStreamField[] fields,
                          ReferenceQueue<Class<?>> queue)
        {
            super(cl, queue);
            nullClass = (cl == null);
            sigs = new String[2 * fields.length];
            for (int i = 0, j = 0; i < fields.length; i++) {
                ObjectStreamField f = fields[i];
                sigs[j++] = f.getName();
                sigs[j++] = f.getSignature();
            }
            hash = System.identityHashCode(cl) + Arrays.hashCode(sigs);
        }

        public int hashCode() {
            return hash;
        }

        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            }

            if (obj instanceof FieldReflectorKey) {
                FieldReflectorKey other = (FieldReflectorKey) obj;
                Class<?> referent;
                return (nullClass ? other.nullClass
                                  : ((referent = get()) != null) &&
                                    (referent == other.get())) &&
                        Arrays.equals(sigs, other.sigs);
            } else {
                return false;
            }
        }
    }

    
Matches given set of serializable fields with serializable fields
obtained from the given local class descriptor (which contain bindings
to reflective Field objects).  Returns list of ObjectStreamFields in
which each ObjectStreamField whose signature matches that of a local
field contains a Field object for that field; unmatched
ObjectStreamFields contain null Field objects.  Shared/unshared settings
of the returned ObjectStreamFields also reflect those of matched local
ObjectStreamFields.  Throws InvalidClassException if unresolvable type
conflicts exist between the two sets of fields.
/**
     * Matches given set of serializable fields with serializable fields
     * obtained from the given local class descriptor (which contain bindings
     * to reflective Field objects).  Returns list of ObjectStreamFields in
     * which each ObjectStreamField whose signature matches that of a local
     * field contains a Field object for that field; unmatched
     * ObjectStreamFields contain null Field objects.  Shared/unshared settings
     * of the returned ObjectStreamFields also reflect those of matched local
     * ObjectStreamFields.  Throws InvalidClassException if unresolvable type
     * conflicts exist between the two sets of fields.
     */
    private static ObjectStreamField[] matchFields(ObjectStreamField[] fields,
                                                   ObjectStreamClass localDesc)
        throws InvalidClassException
    {
        ObjectStreamField[] localFields = (localDesc != null) ?
            localDesc.fields : NO_FIELDS;

        /*
         * Even if fields == localFields, we cannot simply return localFields
         * here.  In previous implementations of serialization,
         * ObjectStreamField.getType() returned Object.class if the
         * ObjectStreamField represented a non-primitive field and belonged to
         * a non-local class descriptor.  To preserve this (questionable)
         * behavior, the ObjectStreamField instances returned by matchFields
         * cannot report non-primitive types other than Object.class; hence
         * localFields cannot be returned directly.
         */

        ObjectStreamField[] matches = new ObjectStreamField[fields.length];
        for (int i = 0; i < fields.length; i++) {
            ObjectStreamField f = fields[i], m = null;
            for (int j = 0; j < localFields.length; j++) {
                ObjectStreamField lf = localFields[j];
                if (f.getName().equals(lf.getName())) {
                    if ((f.isPrimitive() || lf.isPrimitive()) &&
                        f.getTypeCode() != lf.getTypeCode())
                    {
                        throw new InvalidClassException(localDesc.name,
                            "incompatible types for field " + f.getName());
                    }
                    if (lf.getField() != null) {
                        m = new ObjectStreamField(
                            lf.getField(), lf.isUnshared(), false);
                    } else {
                        m = new ObjectStreamField(
                            lf.getName(), lf.getSignature(), lf.isUnshared());
                    }
                }
            }
            if (m == null) {
                m = new ObjectStreamField(
                    f.getName(), f.getSignature(), false);
            }
            m.setOffset(f.getOffset());
            matches[i] = m;
        }
        return matches;
    }

    
Removes from the specified map any keys that have been enqueued
on the specified reference queue.
/**
     * Removes from the specified map any keys that have been enqueued
     * on the specified reference queue.
     */
    static void processQueue(ReferenceQueue<Class<?>> queue,
                             ConcurrentMap<? extends
                             WeakReference<Class<?>>, ?> map)
    {
        Reference<? extends Class<?>> ref;
        while((ref = queue.poll()) != null) {
            map.remove(ref);
        }
    }

    
 Weak key for Class objects.
/**
     *  Weak key for Class objects.
     *
     **/
    static class WeakClassKey extends WeakReference<Class<?>> {
        
saved value of the referent's identity hash code, to maintain
a consistent hash code after the referent has been cleared
/**
         * saved value of the referent's identity hash code, to maintain
         * a consistent hash code after the referent has been cleared
         */
        private final int hash;

        
Create a new WeakClassKey to the given object, registered
with a queue.
/**
         * Create a new WeakClassKey to the given object, registered
         * with a queue.
         */
        WeakClassKey(Class<?> cl, ReferenceQueue<Class<?>> refQueue) {
            super(cl, refQueue);
            hash = System.identityHashCode(cl);
        }

        
Returns the identity hash code of the original referent.
/**
         * Returns the identity hash code of the original referent.
         */
        public int hashCode() {
            return hash;
        }

        
Returns true if the given object is this identical
WeakClassKey instance, or, if this object's referent has not
been cleared, if the given object is another WeakClassKey
instance with the identical non-null referent as this one.
/**
         * Returns true if the given object is this identical
         * WeakClassKey instance, or, if this object's referent has not
         * been cleared, if the given object is another WeakClassKey
         * instance with the identical non-null referent as this one.
         */
        public boolean equals(Object obj) {
            if (obj == this) {
                return true;
            }

            if (obj instanceof WeakClassKey) {
                Object referent = get();
                return (referent != null) &&
                       (referent == ((WeakClassKey) obj).get());
            } else {
                return false;
            }
        }
    }
}