/*
 * Copyright (c) 1999, 2018, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.lang.reflect;

import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import sun.security.action.GetBooleanAction;

ProxyGenerator contains the code to generate a dynamic proxy class
for the java.lang.reflect.Proxy API.
The external interfaces to ProxyGenerator is the static
"generateProxyClass" method.
Author:
     Peter Jones
Since:
      1.3/**
 * ProxyGenerator contains the code to generate a dynamic proxy class
 * for the java.lang.reflect.Proxy API.
 *
 * The external interfaces to ProxyGenerator is the static
 * "generateProxyClass" method.
 *
 * @author      Peter Jones
 * @since       1.3
 */
class ProxyGenerator {
    /*
     * In the comments below, "JVMS" refers to The Java Virtual Machine
     * Specification Second Edition and "JLS" refers to the original
     * version of The Java Language Specification, unless otherwise
     * specified.
     */

    /* generate 1.5-era class file version */
    private static final int CLASSFILE_MAJOR_VERSION = 49;
    private static final int CLASSFILE_MINOR_VERSION = 0;

    /*
     * beginning of constants copied from
     * sun.tools.java.RuntimeConstants (which no longer exists):
     */

    /* constant pool tags */
    private static final int CONSTANT_UTF8              = 1;
    private static final int CONSTANT_UNICODE           = 2;
    private static final int CONSTANT_INTEGER           = 3;
    private static final int CONSTANT_FLOAT             = 4;
    private static final int CONSTANT_LONG              = 5;
    private static final int CONSTANT_DOUBLE            = 6;
    private static final int CONSTANT_CLASS             = 7;
    private static final int CONSTANT_STRING            = 8;
    private static final int CONSTANT_FIELD             = 9;
    private static final int CONSTANT_METHOD            = 10;
    private static final int CONSTANT_INTERFACEMETHOD   = 11;
    private static final int CONSTANT_NAMEANDTYPE       = 12;

    /* access and modifier flags */
    private static final int ACC_PUBLIC                 = 0x00000001;
    private static final int ACC_PRIVATE                = 0x00000002;
//  private static final int ACC_PROTECTED              = 0x00000004;
    private static final int ACC_STATIC                 = 0x00000008;
    private static final int ACC_FINAL                  = 0x00000010;
//  private static final int ACC_SYNCHRONIZED           = 0x00000020;
//  private static final int ACC_VOLATILE               = 0x00000040;
//  private static final int ACC_TRANSIENT              = 0x00000080;
//  private static final int ACC_NATIVE                 = 0x00000100;
//  private static final int ACC_INTERFACE              = 0x00000200;
//  private static final int ACC_ABSTRACT               = 0x00000400;
    private static final int ACC_SUPER                  = 0x00000020;
//  private static final int ACC_STRICT                 = 0x00000800;

    /* opcodes */
//  private static final int opc_nop                    = 0;
    private static final int opc_aconst_null            = 1;
//  private static final int opc_iconst_m1              = 2;
    private static final int opc_iconst_0               = 3;
//  private static final int opc_iconst_1               = 4;
//  private static final int opc_iconst_2               = 5;
//  private static final int opc_iconst_3               = 6;
//  private static final int opc_iconst_4               = 7;
//  private static final int opc_iconst_5               = 8;
//  private static final int opc_lconst_0               = 9;
//  private static final int opc_lconst_1               = 10;
//  private static final int opc_fconst_0               = 11;
//  private static final int opc_fconst_1               = 12;
//  private static final int opc_fconst_2               = 13;
//  private static final int opc_dconst_0               = 14;
//  private static final int opc_dconst_1               = 15;
    private static final int opc_bipush                 = 16;
    private static final int opc_sipush                 = 17;
    private static final int opc_ldc                    = 18;
    private static final int opc_ldc_w                  = 19;
//  private static final int opc_ldc2_w                 = 20;
    private static final int opc_iload                  = 21;
    private static final int opc_lload                  = 22;
    private static final int opc_fload                  = 23;
    private static final int opc_dload                  = 24;
    private static final int opc_aload                  = 25;
    private static final int opc_iload_0                = 26;
//  private static final int opc_iload_1                = 27;
//  private static final int opc_iload_2                = 28;
//  private static final int opc_iload_3                = 29;
    private static final int opc_lload_0                = 30;
//  private static final int opc_lload_1                = 31;
//  private static final int opc_lload_2                = 32;
//  private static final int opc_lload_3                = 33;
    private static final int opc_fload_0                = 34;
//  private static final int opc_fload_1                = 35;
//  private static final int opc_fload_2                = 36;
//  private static final int opc_fload_3                = 37;
    private static final int opc_dload_0                = 38;
//  private static final int opc_dload_1                = 39;
//  private static final int opc_dload_2                = 40;
//  private static final int opc_dload_3                = 41;
    private static final int opc_aload_0                = 42;
//  private static final int opc_aload_1                = 43;
//  private static final int opc_aload_2                = 44;
//  private static final int opc_aload_3                = 45;
//  private static final int opc_iaload                 = 46;
//  private static final int opc_laload                 = 47;
//  private static final int opc_faload                 = 48;
//  private static final int opc_daload                 = 49;
//  private static final int opc_aaload                 = 50;
//  private static final int opc_baload                 = 51;
//  private static final int opc_caload                 = 52;
//  private static final int opc_saload                 = 53;
//  private static final int opc_istore                 = 54;
//  private static final int opc_lstore                 = 55;
//  private static final int opc_fstore                 = 56;
//  private static final int opc_dstore                 = 57;
    private static final int opc_astore                 = 58;
//  private static final int opc_istore_0               = 59;
//  private static final int opc_istore_1               = 60;
//  private static final int opc_istore_2               = 61;
//  private static final int opc_istore_3               = 62;
//  private static final int opc_lstore_0               = 63;
//  private static final int opc_lstore_1               = 64;
//  private static final int opc_lstore_2               = 65;
//  private static final int opc_lstore_3               = 66;
//  private static final int opc_fstore_0               = 67;
//  private static final int opc_fstore_1               = 68;
//  private static final int opc_fstore_2               = 69;
//  private static final int opc_fstore_3               = 70;
//  private static final int opc_dstore_0               = 71;
//  private static final int opc_dstore_1               = 72;
//  private static final int opc_dstore_2               = 73;
//  private static final int opc_dstore_3               = 74;
    private static final int opc_astore_0               = 75;
//  private static final int opc_astore_1               = 76;
//  private static final int opc_astore_2               = 77;
//  private static final int opc_astore_3               = 78;
//  private static final int opc_iastore                = 79;
//  private static final int opc_lastore                = 80;
//  private static final int opc_fastore                = 81;
//  private static final int opc_dastore                = 82;
    private static final int opc_aastore                = 83;
//  private static final int opc_bastore                = 84;
//  private static final int opc_castore                = 85;
//  private static final int opc_sastore                = 86;
    private static final int opc_pop                    = 87;
//  private static final int opc_pop2                   = 88;
    private static final int opc_dup                    = 89;
//  private static final int opc_dup_x1                 = 90;
//  private static final int opc_dup_x2                 = 91;
//  private static final int opc_dup2                   = 92;
//  private static final int opc_dup2_x1                = 93;
//  private static final int opc_dup2_x2                = 94;
//  private static final int opc_swap                   = 95;
//  private static final int opc_iadd                   = 96;
//  private static final int opc_ladd                   = 97;
//  private static final int opc_fadd                   = 98;
//  private static final int opc_dadd                   = 99;
//  private static final int opc_isub                   = 100;
//  private static final int opc_lsub                   = 101;
//  private static final int opc_fsub                   = 102;
//  private static final int opc_dsub                   = 103;
//  private static final int opc_imul                   = 104;
//  private static final int opc_lmul                   = 105;
//  private static final int opc_fmul                   = 106;
//  private static final int opc_dmul                   = 107;
//  private static final int opc_idiv                   = 108;
//  private static final int opc_ldiv                   = 109;
//  private static final int opc_fdiv                   = 110;
//  private static final int opc_ddiv                   = 111;
//  private static final int opc_irem                   = 112;
//  private static final int opc_lrem                   = 113;
//  private static final int opc_frem                   = 114;
//  private static final int opc_drem                   = 115;
//  private static final int opc_ineg                   = 116;
//  private static final int opc_lneg                   = 117;
//  private static final int opc_fneg                   = 118;
//  private static final int opc_dneg                   = 119;
//  private static final int opc_ishl                   = 120;
//  private static final int opc_lshl                   = 121;
//  private static final int opc_ishr                   = 122;
//  private static final int opc_lshr                   = 123;
//  private static final int opc_iushr                  = 124;
//  private static final int opc_lushr                  = 125;
//  private static final int opc_iand                   = 126;
//  private static final int opc_land                   = 127;
//  private static final int opc_ior                    = 128;
//  private static final int opc_lor                    = 129;
//  private static final int opc_ixor                   = 130;
//  private static final int opc_lxor                   = 131;
//  private static final int opc_iinc                   = 132;
//  private static final int opc_i2l                    = 133;
//  private static final int opc_i2f                    = 134;
//  private static final int opc_i2d                    = 135;
//  private static final int opc_l2i                    = 136;
//  private static final int opc_l2f                    = 137;
//  private static final int opc_l2d                    = 138;
//  private static final int opc_f2i                    = 139;
//  private static final int opc_f2l                    = 140;
//  private static final int opc_f2d                    = 141;
//  private static final int opc_d2i                    = 142;
//  private static final int opc_d2l                    = 143;
//  private static final int opc_d2f                    = 144;
//  private static final int opc_i2b                    = 145;
//  private static final int opc_i2c                    = 146;
//  private static final int opc_i2s                    = 147;
//  private static final int opc_lcmp                   = 148;
//  private static final int opc_fcmpl                  = 149;
//  private static final int opc_fcmpg                  = 150;
//  private static final int opc_dcmpl                  = 151;
//  private static final int opc_dcmpg                  = 152;
//  private static final int opc_ifeq                   = 153;
//  private static final int opc_ifne                   = 154;
//  private static final int opc_iflt                   = 155;
//  private static final int opc_ifge                   = 156;
//  private static final int opc_ifgt                   = 157;
//  private static final int opc_ifle                   = 158;
//  private static final int opc_if_icmpeq              = 159;
//  private static final int opc_if_icmpne              = 160;
//  private static final int opc_if_icmplt              = 161;
//  private static final int opc_if_icmpge              = 162;
//  private static final int opc_if_icmpgt              = 163;
//  private static final int opc_if_icmple              = 164;
//  private static final int opc_if_acmpeq              = 165;
//  private static final int opc_if_acmpne              = 166;
//  private static final int opc_goto                   = 167;
//  private static final int opc_jsr                    = 168;
//  private static final int opc_ret                    = 169;
//  private static final int opc_tableswitch            = 170;
//  private static final int opc_lookupswitch           = 171;
    private static final int opc_ireturn                = 172;
    private static final int opc_lreturn                = 173;
    private static final int opc_freturn                = 174;
    private static final int opc_dreturn                = 175;
    private static final int opc_areturn                = 176;
    private static final int opc_return                 = 177;
    private static final int opc_getstatic              = 178;
    private static final int opc_putstatic              = 179;
    private static final int opc_getfield               = 180;
//  private static final int opc_putfield               = 181;
    private static final int opc_invokevirtual          = 182;
    private static final int opc_invokespecial          = 183;
    private static final int opc_invokestatic           = 184;
    private static final int opc_invokeinterface        = 185;
    private static final int opc_new                    = 187;
//  private static final int opc_newarray               = 188;
    private static final int opc_anewarray              = 189;
//  private static final int opc_arraylength            = 190;
    private static final int opc_athrow                 = 191;
    private static final int opc_checkcast              = 192;
//  private static final int opc_instanceof             = 193;
//  private static final int opc_monitorenter           = 194;
//  private static final int opc_monitorexit            = 195;
    private static final int opc_wide                   = 196;
//  private static final int opc_multianewarray         = 197;
//  private static final int opc_ifnull                 = 198;
//  private static final int opc_ifnonnull              = 199;
//  private static final int opc_goto_w                 = 200;
//  private static final int opc_jsr_w                  = 201;

    // end of constants copied from sun.tools.java.RuntimeConstants

    
name of the superclass of proxy classes /** name of the superclass of proxy classes */
    private static final String superclassName = "java/lang/reflect/Proxy";

    
name of field for storing a proxy instance's invocation handler /** name of field for storing a proxy instance's invocation handler */
    private static final String handlerFieldName = "h";

    
debugging flag for saving generated class files /** debugging flag for saving generated class files */
    private static final boolean saveGeneratedFiles =
        java.security.AccessController.doPrivileged(
            new GetBooleanAction(
                "jdk.proxy.ProxyGenerator.saveGeneratedFiles")).booleanValue();

    
Generate a public proxy class given a name and a list of proxy interfaces.
/**
     * Generate a public proxy class given a name and a list of proxy interfaces.
     */
    static byte[] generateProxyClass(final String name,
                                     Class<?>[] interfaces) {
        return generateProxyClass(name, interfaces, (ACC_PUBLIC | ACC_FINAL | ACC_SUPER));
    }

    
Generate a proxy class given a name and a list of proxy interfaces.
Params:
name –        the class name of the proxy class
interfaces –  proxy interfaces
accessFlags – access flags of the proxy class/**
     * Generate a proxy class given a name and a list of proxy interfaces.
     *
     * @param name        the class name of the proxy class
     * @param interfaces  proxy interfaces
     * @param accessFlags access flags of the proxy class
    */
    static byte[] generateProxyClass(final String name,
                                     Class<?>[] interfaces,
                                     int accessFlags)
    {
        ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);
        final byte[] classFile = gen.generateClassFile();

        if (saveGeneratedFiles) {
            java.security.AccessController.doPrivileged(
            new java.security.PrivilegedAction<Void>() {
                public Void run() {
                    try {
                        int i = name.lastIndexOf('.');
                        Path path;
                        if (i > 0) {
                            Path dir = Path.of(name.substring(0, i).replace('.', File.separatorChar));
                            Files.createDirectories(dir);
                            path = dir.resolve(name.substring(i+1, name.length()) + ".class");
                        } else {
                            path = Path.of(name + ".class");
                        }
                        Files.write(path, classFile);
                        return null;
                    } catch (IOException e) {
                        throw new InternalError(
                            "I/O exception saving generated file: " + e);
                    }
                }
            });
        }

        return classFile;
    }

    /* preloaded Method objects for methods in java.lang.Object */
    private static Method hashCodeMethod;
    private static Method equalsMethod;
    private static Method toStringMethod;
    static {
        try {
            hashCodeMethod = Object.class.getMethod("hashCode");
            equalsMethod =
                Object.class.getMethod("equals", new Class<?>[] { Object.class });
            toStringMethod = Object.class.getMethod("toString");
        } catch (NoSuchMethodException e) {
            throw new NoSuchMethodError(e.getMessage());
        }
    }

    
name of proxy class /** name of proxy class */
    private String className;

    
proxy interfaces /** proxy interfaces */
    private Class<?>[] interfaces;

    
proxy class access flags /** proxy class access flags */
    private int accessFlags;

    
constant pool of class being generated /** constant pool of class being generated */
    private ConstantPool cp = new ConstantPool();

    
FieldInfo struct for each field of generated class /** FieldInfo struct for each field of generated class */
    private List<FieldInfo> fields = new ArrayList<>();

    
MethodInfo struct for each method of generated class /** MethodInfo struct for each method of generated class */
    private List<MethodInfo> methods = new ArrayList<>();

    
maps method signature string to list of ProxyMethod objects for
proxy methods with that signature
/**
     * maps method signature string to list of ProxyMethod objects for
     * proxy methods with that signature
     */
    private Map<String, List<ProxyMethod>> proxyMethods = new HashMap<>();

    
count of ProxyMethod objects added to proxyMethods /** count of ProxyMethod objects added to proxyMethods */
    private int proxyMethodCount = 0;

    
Construct a ProxyGenerator to generate a proxy class with the
specified name and for the given interfaces.
A ProxyGenerator object contains the state for the ongoing
generation of a particular proxy class.
/**
     * Construct a ProxyGenerator to generate a proxy class with the
     * specified name and for the given interfaces.
     *
     * A ProxyGenerator object contains the state for the ongoing
     * generation of a particular proxy class.
     */
    private ProxyGenerator(String className, Class<?>[] interfaces, int accessFlags) {
        this.className = className;
        this.interfaces = interfaces;
        this.accessFlags = accessFlags;
    }

    
Generate a class file for the proxy class.  This method drives the
class file generation process.
/**
     * Generate a class file for the proxy class.  This method drives the
     * class file generation process.
     */
    private byte[] generateClassFile() {

        /* ============================================================
         * Step 1: Assemble ProxyMethod objects for all methods to
         * generate proxy dispatching code for.
         */

        /*
         * Record that proxy methods are needed for the hashCode, equals,
         * and toString methods of java.lang.Object.  This is done before
         * the methods from the proxy interfaces so that the methods from
         * java.lang.Object take precedence over duplicate methods in the
         * proxy interfaces.
         */
        addProxyMethod(hashCodeMethod, Object.class);
        addProxyMethod(equalsMethod, Object.class);
        addProxyMethod(toStringMethod, Object.class);

        /*
         * Now record all of the methods from the proxy interfaces, giving
         * earlier interfaces precedence over later ones with duplicate
         * methods.
         */
        for (Class<?> intf : interfaces) {
            for (Method m : intf.getMethods()) {
                if (!Modifier.isStatic(m.getModifiers())) {
                    addProxyMethod(m, intf);
                }
            }
        }

        /*
         * For each set of proxy methods with the same signature,
         * verify that the methods' return types are compatible.
         */
        for (List<ProxyMethod> sigmethods : proxyMethods.values()) {
            checkReturnTypes(sigmethods);
        }

        /* ============================================================
         * Step 2: Assemble FieldInfo and MethodInfo structs for all of
         * fields and methods in the class we are generating.
         */
        try {
            methods.add(generateConstructor());

            for (List<ProxyMethod> sigmethods : proxyMethods.values()) {
                for (ProxyMethod pm : sigmethods) {

                    // add static field for method's Method object
                    fields.add(new FieldInfo(pm.methodFieldName,
                        "Ljava/lang/reflect/Method;",
                         ACC_PRIVATE | ACC_STATIC));

                    // generate code for proxy method and add it
                    methods.add(pm.generateMethod());
                }
            }

            methods.add(generateStaticInitializer());

        } catch (IOException e) {
            throw new InternalError("unexpected I/O Exception", e);
        }

        if (methods.size() > 65535) {
            throw new IllegalArgumentException("method limit exceeded");
        }
        if (fields.size() > 65535) {
            throw new IllegalArgumentException("field limit exceeded");
        }

        /* ============================================================
         * Step 3: Write the final class file.
         */

        /*
         * Make sure that constant pool indexes are reserved for the
         * following items before starting to write the final class file.
         */
        cp.getClass(dotToSlash(className));
        cp.getClass(superclassName);
        for (Class<?> intf: interfaces) {
            cp.getClass(dotToSlash(intf.getName()));
        }

        /*
         * Disallow new constant pool additions beyond this point, since
         * we are about to write the final constant pool table.
         */
        cp.setReadOnly();

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

        try {
            /*
             * Write all the items of the "ClassFile" structure.
             * See JVMS section 4.1.
             */
                                        // u4 magic;
            dout.writeInt(0xCAFEBABE);
                                        // u2 minor_version;
            dout.writeShort(CLASSFILE_MINOR_VERSION);
                                        // u2 major_version;
            dout.writeShort(CLASSFILE_MAJOR_VERSION);

            cp.write(dout);             // (write constant pool)

                                        // u2 access_flags;
            dout.writeShort(accessFlags);
                                        // u2 this_class;
            dout.writeShort(cp.getClass(dotToSlash(className)));
                                        // u2 super_class;
            dout.writeShort(cp.getClass(superclassName));

                                        // u2 interfaces_count;
            dout.writeShort(interfaces.length);
                                        // u2 interfaces[interfaces_count];
            for (Class<?> intf : interfaces) {
                dout.writeShort(cp.getClass(
                    dotToSlash(intf.getName())));
            }

                                        // u2 fields_count;
            dout.writeShort(fields.size());
                                        // field_info fields[fields_count];
            for (FieldInfo f : fields) {
                f.write(dout);
            }

                                        // u2 methods_count;
            dout.writeShort(methods.size());
                                        // method_info methods[methods_count];
            for (MethodInfo m : methods) {
                m.write(dout);
            }

                                         // u2 attributes_count;
            dout.writeShort(0); // (no ClassFile attributes for proxy classes)

        } catch (IOException e) {
            throw new InternalError("unexpected I/O Exception", e);
        }

        return bout.toByteArray();
    }

    
Add another method to be proxied, either by creating a new
ProxyMethod object or augmenting an old one for a duplicate
method.
"fromClass" indicates the proxy interface that the method was
found through, which may be different from (a subinterface of)
the method's "declaring class".  Note that the first Method
object passed for a given name and descriptor identifies the
Method object (and thus the declaring class) that will be
passed to the invocation handler's "invoke" method for a given
set of duplicate methods.
/**
     * Add another method to be proxied, either by creating a new
     * ProxyMethod object or augmenting an old one for a duplicate
     * method.
     *
     * "fromClass" indicates the proxy interface that the method was
     * found through, which may be different from (a subinterface of)
     * the method's "declaring class".  Note that the first Method
     * object passed for a given name and descriptor identifies the
     * Method object (and thus the declaring class) that will be
     * passed to the invocation handler's "invoke" method for a given
     * set of duplicate methods.
     */
    private void addProxyMethod(Method m, Class<?> fromClass) {
        String name = m.getName();
        Class<?>[] parameterTypes = m.getParameterTypes();
        Class<?> returnType = m.getReturnType();
        Class<?>[] exceptionTypes = m.getExceptionTypes();

        String sig = name + getParameterDescriptors(parameterTypes);
        List<ProxyMethod> sigmethods = proxyMethods.get(sig);
        if (sigmethods != null) {
            for (ProxyMethod pm : sigmethods) {
                if (returnType == pm.returnType) {
                    /*
                     * Found a match: reduce exception types to the
                     * greatest set of exceptions that can thrown
                     * compatibly with the throws clauses of both
                     * overridden methods.
                     */
                    List<Class<?>> legalExceptions = new ArrayList<>();
                    collectCompatibleTypes(
                        exceptionTypes, pm.exceptionTypes, legalExceptions);
                    collectCompatibleTypes(
                        pm.exceptionTypes, exceptionTypes, legalExceptions);
                    pm.exceptionTypes = new Class<?>[legalExceptions.size()];
                    pm.exceptionTypes =
                        legalExceptions.toArray(pm.exceptionTypes);
                    return;
                }
            }
        } else {
            sigmethods = new ArrayList<>(3);
            proxyMethods.put(sig, sigmethods);
        }
        sigmethods.add(new ProxyMethod(name, parameterTypes, returnType,
                                       exceptionTypes, fromClass));
    }

    
For a given set of proxy methods with the same signature, check
that their return types are compatible according to the Proxy
specification.
Specifically, if there is more than one such method, then all
of the return types must be reference types, and there must be
one return type that is assignable to each of the rest of them.
/**
     * For a given set of proxy methods with the same signature, check
     * that their return types are compatible according to the Proxy
     * specification.
     *
     * Specifically, if there is more than one such method, then all
     * of the return types must be reference types, and there must be
     * one return type that is assignable to each of the rest of them.
     */
    private static void checkReturnTypes(List<ProxyMethod> methods) {
        /*
         * If there is only one method with a given signature, there
         * cannot be a conflict.  This is the only case in which a
         * primitive (or void) return type is allowed.
         */
        if (methods.size() < 2) {
            return;
        }

        /*
         * List of return types that are not yet known to be
         * assignable from ("covered" by) any of the others.
         */
        LinkedList<Class<?>> uncoveredReturnTypes = new LinkedList<>();

    nextNewReturnType:
        for (ProxyMethod pm : methods) {
            Class<?> newReturnType = pm.returnType;
            if (newReturnType.isPrimitive()) {
                throw new IllegalArgumentException(
                    "methods with same signature " +
                    getFriendlyMethodSignature(pm.methodName,
                                               pm.parameterTypes) +
                    " but incompatible return types: " +
                    newReturnType.getName() + " and others");
            }
            boolean added = false;

            /*
             * Compare the new return type to the existing uncovered
             * return types.
             */
            ListIterator<Class<?>> liter = uncoveredReturnTypes.listIterator();
            while (liter.hasNext()) {
                Class<?> uncoveredReturnType = liter.next();

                /*
                 * If an existing uncovered return type is assignable
                 * to this new one, then we can forget the new one.
                 */
                if (newReturnType.isAssignableFrom(uncoveredReturnType)) {
                    assert !added;
                    continue nextNewReturnType;
                }

                /*
                 * If the new return type is assignable to an existing
                 * uncovered one, then should replace the existing one
                 * with the new one (or just forget the existing one,
                 * if the new one has already be put in the list).
                 */
                if (uncoveredReturnType.isAssignableFrom(newReturnType)) {
                    // (we can assume that each return type is unique)
                    if (!added) {
                        liter.set(newReturnType);
                        added = true;
                    } else {
                        liter.remove();
                    }
                }
            }

            /*
             * If we got through the list of existing uncovered return
             * types without an assignability relationship, then add
             * the new return type to the list of uncovered ones.
             */
            if (!added) {
                uncoveredReturnTypes.add(newReturnType);
            }
        }

        /*
         * We shouldn't end up with more than one return type that is
         * not assignable from any of the others.
         */
        if (uncoveredReturnTypes.size() > 1) {
            ProxyMethod pm = methods.get(0);
            throw new IllegalArgumentException(
                "methods with same signature " +
                getFriendlyMethodSignature(pm.methodName, pm.parameterTypes) +
                " but incompatible return types: " + uncoveredReturnTypes);
        }
    }

    
A FieldInfo object contains information about a particular field
in the class being generated.  The class mirrors the data items of
the "field_info" structure of the class file format (see JVMS 4.5).
/**
     * A FieldInfo object contains information about a particular field
     * in the class being generated.  The class mirrors the data items of
     * the "field_info" structure of the class file format (see JVMS 4.5).
     */
    private class FieldInfo {
        public int accessFlags;
        public String name;
        public String descriptor;

        public FieldInfo(String name, String descriptor, int accessFlags) {
            this.name = name;
            this.descriptor = descriptor;
            this.accessFlags = accessFlags;

            /*
             * Make sure that constant pool indexes are reserved for the
             * following items before starting to write the final class file.
             */
            cp.getUtf8(name);
            cp.getUtf8(descriptor);
        }

        public void write(DataOutputStream out) throws IOException {
            /*
             * Write all the items of the "field_info" structure.
             * See JVMS section 4.5.
             */
                                        // u2 access_flags;
            out.writeShort(accessFlags);
                                        // u2 name_index;
            out.writeShort(cp.getUtf8(name));
                                        // u2 descriptor_index;
            out.writeShort(cp.getUtf8(descriptor));
                                        // u2 attributes_count;
            out.writeShort(0);  // (no field_info attributes for proxy classes)
        }
    }

    
An ExceptionTableEntry object holds values for the data items of
an entry in the "exception_table" item of the "Code" attribute of
"method_info" structures (see JVMS 4.7.3).
/**
     * An ExceptionTableEntry object holds values for the data items of
     * an entry in the "exception_table" item of the "Code" attribute of
     * "method_info" structures (see JVMS 4.7.3).
     */
    private static class ExceptionTableEntry {
        public short startPc;
        public short endPc;
        public short handlerPc;
        public short catchType;

        public ExceptionTableEntry(short startPc, short endPc,
                                   short handlerPc, short catchType)
        {
            this.startPc = startPc;
            this.endPc = endPc;
            this.handlerPc = handlerPc;
            this.catchType = catchType;
        }
    };

    
A MethodInfo object contains information about a particular method
in the class being generated.  This class mirrors the data items of
the "method_info" structure of the class file format (see JVMS 4.6).
/**
     * A MethodInfo object contains information about a particular method
     * in the class being generated.  This class mirrors the data items of
     * the "method_info" structure of the class file format (see JVMS 4.6).
     */
    private class MethodInfo {
        public int accessFlags;
        public String name;
        public String descriptor;
        public short maxStack;
        public short maxLocals;
        public ByteArrayOutputStream code = new ByteArrayOutputStream();
        public List<ExceptionTableEntry> exceptionTable =
            new ArrayList<ExceptionTableEntry>();
        public short[] declaredExceptions;

        public MethodInfo(String name, String descriptor, int accessFlags) {
            this.name = name;
            this.descriptor = descriptor;
            this.accessFlags = accessFlags;

            /*
             * Make sure that constant pool indexes are reserved for the
             * following items before starting to write the final class file.
             */
            cp.getUtf8(name);
            cp.getUtf8(descriptor);
            cp.getUtf8("Code");
            cp.getUtf8("Exceptions");
        }

        public void write(DataOutputStream out) throws IOException {
            /*
             * Write all the items of the "method_info" structure.
             * See JVMS section 4.6.
             */
                                        // u2 access_flags;
            out.writeShort(accessFlags);
                                        // u2 name_index;
            out.writeShort(cp.getUtf8(name));
                                        // u2 descriptor_index;
            out.writeShort(cp.getUtf8(descriptor));
                                        // u2 attributes_count;
            out.writeShort(2);  // (two method_info attributes:)

            // Write "Code" attribute. See JVMS section 4.7.3.

                                        // u2 attribute_name_index;
            out.writeShort(cp.getUtf8("Code"));
                                        // u4 attribute_length;
            out.writeInt(12 + code.size() + 8 * exceptionTable.size());
                                        // u2 max_stack;
            out.writeShort(maxStack);
                                        // u2 max_locals;
            out.writeShort(maxLocals);
                                        // u2 code_length;
            out.writeInt(code.size());
                                        // u1 code[code_length];
            code.writeTo(out);
                                        // u2 exception_table_length;
            out.writeShort(exceptionTable.size());
            for (ExceptionTableEntry e : exceptionTable) {
                                        // u2 start_pc;
                out.writeShort(e.startPc);
                                        // u2 end_pc;
                out.writeShort(e.endPc);
                                        // u2 handler_pc;
                out.writeShort(e.handlerPc);
                                        // u2 catch_type;
                out.writeShort(e.catchType);
            }
                                        // u2 attributes_count;
            out.writeShort(0);

            // write "Exceptions" attribute.  See JVMS section 4.7.4.

                                        // u2 attribute_name_index;
            out.writeShort(cp.getUtf8("Exceptions"));
                                        // u4 attributes_length;
            out.writeInt(2 + 2 * declaredExceptions.length);
                                        // u2 number_of_exceptions;
            out.writeShort(declaredExceptions.length);
                        // u2 exception_index_table[number_of_exceptions];
            for (short value : declaredExceptions) {
                out.writeShort(value);
            }
        }

    }

    
A ProxyMethod object represents a proxy method in the proxy class
being generated: a method whose implementation will encode and
dispatch invocations to the proxy instance's invocation handler.
/**
     * A ProxyMethod object represents a proxy method in the proxy class
     * being generated: a method whose implementation will encode and
     * dispatch invocations to the proxy instance's invocation handler.
     */
    private class ProxyMethod {

        public String methodName;
        public Class<?>[] parameterTypes;
        public Class<?> returnType;
        public Class<?>[] exceptionTypes;
        public Class<?> fromClass;
        public String methodFieldName;

        private ProxyMethod(String methodName, Class<?>[] parameterTypes,
                            Class<?> returnType, Class<?>[] exceptionTypes,
                            Class<?> fromClass)
        {
            this.methodName = methodName;
            this.parameterTypes = parameterTypes;
            this.returnType = returnType;
            this.exceptionTypes = exceptionTypes;
            this.fromClass = fromClass;
            this.methodFieldName = "m" + proxyMethodCount++;
        }

        
Return a MethodInfo object for this method, including generating
the code and exception table entry.
/**
         * Return a MethodInfo object for this method, including generating
         * the code and exception table entry.
         */
        private MethodInfo generateMethod() throws IOException {
            String desc = getMethodDescriptor(parameterTypes, returnType);
            MethodInfo minfo = new MethodInfo(methodName, desc,
                ACC_PUBLIC | ACC_FINAL);

            int[] parameterSlot = new int[parameterTypes.length];
            int nextSlot = 1;
            for (int i = 0; i < parameterSlot.length; i++) {
                parameterSlot[i] = nextSlot;
                nextSlot += getWordsPerType(parameterTypes[i]);
            }
            int localSlot0 = nextSlot;
            short pc, tryBegin = 0, tryEnd;

            DataOutputStream out = new DataOutputStream(minfo.code);

            code_aload(0, out);

            out.writeByte(opc_getfield);
            out.writeShort(cp.getFieldRef(
                superclassName,
                handlerFieldName, "Ljava/lang/reflect/InvocationHandler;"));

            code_aload(0, out);

            out.writeByte(opc_getstatic);
            out.writeShort(cp.getFieldRef(
                dotToSlash(className),
                methodFieldName, "Ljava/lang/reflect/Method;"));

            if (parameterTypes.length > 0) {

                code_ipush(parameterTypes.length, out);

                out.writeByte(opc_anewarray);
                out.writeShort(cp.getClass("java/lang/Object"));

                for (int i = 0; i < parameterTypes.length; i++) {

                    out.writeByte(opc_dup);

                    code_ipush(i, out);

                    codeWrapArgument(parameterTypes[i], parameterSlot[i], out);

                    out.writeByte(opc_aastore);
                }
            } else {

                out.writeByte(opc_aconst_null);
            }

            out.writeByte(opc_invokeinterface);
            out.writeShort(cp.getInterfaceMethodRef(
                "java/lang/reflect/InvocationHandler",
                "invoke",
                "(Ljava/lang/Object;Ljava/lang/reflect/Method;" +
                    "[Ljava/lang/Object;)Ljava/lang/Object;"));
            out.writeByte(4);
            out.writeByte(0);

            if (returnType == void.class) {

                out.writeByte(opc_pop);

                out.writeByte(opc_return);

            } else {

                codeUnwrapReturnValue(returnType, out);
            }

            tryEnd = pc = (short) minfo.code.size();

            List<Class<?>> catchList = computeUniqueCatchList(exceptionTypes);
            if (catchList.size() > 0) {

                for (Class<?> ex : catchList) {
                    minfo.exceptionTable.add(new ExceptionTableEntry(
                        tryBegin, tryEnd, pc,
                        cp.getClass(dotToSlash(ex.getName()))));
                }

                out.writeByte(opc_athrow);

                pc = (short) minfo.code.size();

                minfo.exceptionTable.add(new ExceptionTableEntry(
                    tryBegin, tryEnd, pc, cp.getClass("java/lang/Throwable")));

                code_astore(localSlot0, out);

                out.writeByte(opc_new);
                out.writeShort(cp.getClass(
                    "java/lang/reflect/UndeclaredThrowableException"));

                out.writeByte(opc_dup);

                code_aload(localSlot0, out);

                out.writeByte(opc_invokespecial);

                out.writeShort(cp.getMethodRef(
                    "java/lang/reflect/UndeclaredThrowableException",
                    "<init>", "(Ljava/lang/Throwable;)V"));

                out.writeByte(opc_athrow);
            }

            if (minfo.code.size() > 65535) {
                throw new IllegalArgumentException("code size limit exceeded");
            }

            minfo.maxStack = 10;
            minfo.maxLocals = (short) (localSlot0 + 1);
            minfo.declaredExceptions = new short[exceptionTypes.length];
            for (int i = 0; i < exceptionTypes.length; i++) {
                minfo.declaredExceptions[i] = cp.getClass(
                    dotToSlash(exceptionTypes[i].getName()));
            }

            return minfo;
        }

        
Generate code for wrapping an argument of the given type
whose value can be found at the specified local variable
index, in order for it to be passed (as an Object) to the
invocation handler's "invoke" method.  The code is written
to the supplied stream.
/**
         * Generate code for wrapping an argument of the given type
         * whose value can be found at the specified local variable
         * index, in order for it to be passed (as an Object) to the
         * invocation handler's "invoke" method.  The code is written
         * to the supplied stream.
         */
        private void codeWrapArgument(Class<?> type, int slot,
                                      DataOutputStream out)
            throws IOException
        {
            if (type.isPrimitive()) {
                PrimitiveTypeInfo prim = PrimitiveTypeInfo.get(type);

                if (type == int.class ||
                    type == boolean.class ||
                    type == byte.class ||
                    type == char.class ||
                    type == short.class)
                {
                    code_iload(slot, out);
                } else if (type == long.class) {
                    code_lload(slot, out);
                } else if (type == float.class) {
                    code_fload(slot, out);
                } else if (type == double.class) {
                    code_dload(slot, out);
                } else {
                    throw new AssertionError();
                }

                out.writeByte(opc_invokestatic);
                out.writeShort(cp.getMethodRef(
                    prim.wrapperClassName,
                    "valueOf", prim.wrapperValueOfDesc));

            } else {

                code_aload(slot, out);
            }
        }

        
Generate code for unwrapping a return value of the given
type from the invocation handler's "invoke" method (as type
Object) to its correct type.  The code is written to the
supplied stream.
/**
         * Generate code for unwrapping a return value of the given
         * type from the invocation handler's "invoke" method (as type
         * Object) to its correct type.  The code is written to the
         * supplied stream.
         */
        private void codeUnwrapReturnValue(Class<?> type, DataOutputStream out)
            throws IOException
        {
            if (type.isPrimitive()) {
                PrimitiveTypeInfo prim = PrimitiveTypeInfo.get(type);

                out.writeByte(opc_checkcast);
                out.writeShort(cp.getClass(prim.wrapperClassName));

                out.writeByte(opc_invokevirtual);
                out.writeShort(cp.getMethodRef(
                    prim.wrapperClassName,
                    prim.unwrapMethodName, prim.unwrapMethodDesc));

                if (type == int.class ||
                    type == boolean.class ||
                    type == byte.class ||
                    type == char.class ||
                    type == short.class)
                {
                    out.writeByte(opc_ireturn);
                } else if (type == long.class) {
                    out.writeByte(opc_lreturn);
                } else if (type == float.class) {
                    out.writeByte(opc_freturn);
                } else if (type == double.class) {
                    out.writeByte(opc_dreturn);
                } else {
                    throw new AssertionError();
                }

            } else {

                out.writeByte(opc_checkcast);
                out.writeShort(cp.getClass(dotToSlash(type.getName())));

                out.writeByte(opc_areturn);
            }
        }

        
Generate code for initializing the static field that stores
the Method object for this proxy method.  The code is written
to the supplied stream.
/**
         * Generate code for initializing the static field that stores
         * the Method object for this proxy method.  The code is written
         * to the supplied stream.
         */
        private void codeFieldInitialization(DataOutputStream out)
            throws IOException
        {
            codeClassForName(fromClass, out);

            code_ldc(cp.getString(methodName), out);

            code_ipush(parameterTypes.length, out);

            out.writeByte(opc_anewarray);
            out.writeShort(cp.getClass("java/lang/Class"));

            for (int i = 0; i < parameterTypes.length; i++) {

                out.writeByte(opc_dup);

                code_ipush(i, out);

                if (parameterTypes[i].isPrimitive()) {
                    PrimitiveTypeInfo prim =
                        PrimitiveTypeInfo.get(parameterTypes[i]);

                    out.writeByte(opc_getstatic);
                    out.writeShort(cp.getFieldRef(
                        prim.wrapperClassName, "TYPE", "Ljava/lang/Class;"));

                } else {
                    codeClassForName(parameterTypes[i], out);
                }

                out.writeByte(opc_aastore);
            }

            out.writeByte(opc_invokevirtual);
            out.writeShort(cp.getMethodRef(
                "java/lang/Class",
                "getMethod",
                "(Ljava/lang/String;[Ljava/lang/Class;)" +
                "Ljava/lang/reflect/Method;"));

            out.writeByte(opc_putstatic);
            out.writeShort(cp.getFieldRef(
                dotToSlash(className),
                methodFieldName, "Ljava/lang/reflect/Method;"));
        }
    }

    
Generate the constructor method for the proxy class.
/**
     * Generate the constructor method for the proxy class.
     */
    private MethodInfo generateConstructor() throws IOException {
        MethodInfo minfo = new MethodInfo(
            "<init>", "(Ljava/lang/reflect/InvocationHandler;)V",
            ACC_PUBLIC);

        DataOutputStream out = new DataOutputStream(minfo.code);

        code_aload(0, out);

        code_aload(1, out);

        out.writeByte(opc_invokespecial);
        out.writeShort(cp.getMethodRef(
            superclassName,
            "<init>", "(Ljava/lang/reflect/InvocationHandler;)V"));

        out.writeByte(opc_return);

        minfo.maxStack = 10;
        minfo.maxLocals = 2;
        minfo.declaredExceptions = new short[0];

        return minfo;
    }

    
Generate the static initializer method for the proxy class.
/**
     * Generate the static initializer method for the proxy class.
     */
    private MethodInfo generateStaticInitializer() throws IOException {
        MethodInfo minfo = new MethodInfo(
            "<clinit>", "()V", ACC_STATIC);

        int localSlot0 = 1;
        short pc, tryBegin = 0, tryEnd;

        DataOutputStream out = new DataOutputStream(minfo.code);

        for (List<ProxyMethod> sigmethods : proxyMethods.values()) {
            for (ProxyMethod pm : sigmethods) {
                pm.codeFieldInitialization(out);
            }
        }

        out.writeByte(opc_return);

        tryEnd = pc = (short) minfo.code.size();

        minfo.exceptionTable.add(new ExceptionTableEntry(
            tryBegin, tryEnd, pc,
            cp.getClass("java/lang/NoSuchMethodException")));

        code_astore(localSlot0, out);

        out.writeByte(opc_new);
        out.writeShort(cp.getClass("java/lang/NoSuchMethodError"));

        out.writeByte(opc_dup);

        code_aload(localSlot0, out);

        out.writeByte(opc_invokevirtual);
        out.writeShort(cp.getMethodRef(
            "java/lang/Throwable", "getMessage", "()Ljava/lang/String;"));

        out.writeByte(opc_invokespecial);
        out.writeShort(cp.getMethodRef(
            "java/lang/NoSuchMethodError", "<init>", "(Ljava/lang/String;)V"));

        out.writeByte(opc_athrow);

        pc = (short) minfo.code.size();

        minfo.exceptionTable.add(new ExceptionTableEntry(
            tryBegin, tryEnd, pc,
            cp.getClass("java/lang/ClassNotFoundException")));

        code_astore(localSlot0, out);

        out.writeByte(opc_new);
        out.writeShort(cp.getClass("java/lang/NoClassDefFoundError"));

        out.writeByte(opc_dup);

        code_aload(localSlot0, out);

        out.writeByte(opc_invokevirtual);
        out.writeShort(cp.getMethodRef(
            "java/lang/Throwable", "getMessage", "()Ljava/lang/String;"));

        out.writeByte(opc_invokespecial);
        out.writeShort(cp.getMethodRef(
            "java/lang/NoClassDefFoundError",
            "<init>", "(Ljava/lang/String;)V"));

        out.writeByte(opc_athrow);

        if (minfo.code.size() > 65535) {
            throw new IllegalArgumentException("code size limit exceeded");
        }

        minfo.maxStack = 10;
        minfo.maxLocals = (short) (localSlot0 + 1);
        minfo.declaredExceptions = new short[0];

        return minfo;
    }


    /*
     * =============== Code Generation Utility Methods ===============
     */

    /*
     * The following methods generate code for the load or store operation
     * indicated by their name for the given local variable.  The code is
     * written to the supplied stream.
     */

    private void code_iload(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_iload, opc_iload_0, out);
    }

    private void code_lload(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_lload, opc_lload_0, out);
    }

    private void code_fload(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_fload, opc_fload_0, out);
    }

    private void code_dload(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_dload, opc_dload_0, out);
    }

    private void code_aload(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_aload, opc_aload_0, out);
    }

//  private void code_istore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_istore, opc_istore_0, out);
//  }

//  private void code_lstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_lstore, opc_lstore_0, out);
//  }

//  private void code_fstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_fstore, opc_fstore_0, out);
//  }

//  private void code_dstore(int lvar, DataOutputStream out)
//      throws IOException
//  {
//      codeLocalLoadStore(lvar, opc_dstore, opc_dstore_0, out);
//  }

    private void code_astore(int lvar, DataOutputStream out)
        throws IOException
    {
        codeLocalLoadStore(lvar, opc_astore, opc_astore_0, out);
    }

    
Generate code for a load or store instruction for the given local
variable.  The code is written to the supplied stream.
"opcode" indicates the opcode form of the desired load or store
instruction that takes an explicit local variable index, and
"opcode_0" indicates the corresponding form of the instruction
with the implicit index 0.
/**
     * Generate code for a load or store instruction for the given local
     * variable.  The code is written to the supplied stream.
     *
     * "opcode" indicates the opcode form of the desired load or store
     * instruction that takes an explicit local variable index, and
     * "opcode_0" indicates the corresponding form of the instruction
     * with the implicit index 0.
     */
    private void codeLocalLoadStore(int lvar, int opcode, int opcode_0,
                                    DataOutputStream out)
        throws IOException
    {
        assert lvar >= 0 && lvar <= 0xFFFF;
        if (lvar <= 3) {
            out.writeByte(opcode_0 + lvar);
        } else if (lvar <= 0xFF) {
            out.writeByte(opcode);
            out.writeByte(lvar & 0xFF);
        } else {
            /*
             * Use the "wide" instruction modifier for local variable
             * indexes that do not fit into an unsigned byte.
             */
            out.writeByte(opc_wide);
            out.writeByte(opcode);
            out.writeShort(lvar & 0xFFFF);
        }
    }

    
Generate code for an "ldc" instruction for the given constant pool
index (the "ldc_w" instruction is used if the index does not fit
into an unsigned byte).  The code is written to the supplied stream.
/**
     * Generate code for an "ldc" instruction for the given constant pool
     * index (the "ldc_w" instruction is used if the index does not fit
     * into an unsigned byte).  The code is written to the supplied stream.
     */
    private void code_ldc(int index, DataOutputStream out)
        throws IOException
    {
        assert index >= 0 && index <= 0xFFFF;
        if (index <= 0xFF) {
            out.writeByte(opc_ldc);
            out.writeByte(index & 0xFF);
        } else {
            out.writeByte(opc_ldc_w);
            out.writeShort(index & 0xFFFF);
        }
    }

    
Generate code to push a constant integer value on to the operand
stack, using the "iconst_", "bipush", or "sipush" instructions
depending on the size of the value.  The code is written to the
supplied stream.
/**
     * Generate code to push a constant integer value on to the operand
     * stack, using the "iconst_<i>", "bipush", or "sipush" instructions
     * depending on the size of the value.  The code is written to the
     * supplied stream.
     */
    private void code_ipush(int value, DataOutputStream out)
        throws IOException
    {
        if (value >= -1 && value <= 5) {
            out.writeByte(opc_iconst_0 + value);
        } else if (value >= Byte.MIN_VALUE && value <= Byte.MAX_VALUE) {
            out.writeByte(opc_bipush);
            out.writeByte(value & 0xFF);
        } else if (value >= Short.MIN_VALUE && value <= Short.MAX_VALUE) {
            out.writeByte(opc_sipush);
            out.writeShort(value & 0xFFFF);
        } else {
            throw new AssertionError();
        }
    }

    
Generate code to invoke the Class.forName with the name of the given
class to get its Class object at runtime.  The code is written to
the supplied stream.  Note that the code generated by this method
may cause the checked ClassNotFoundException to be thrown.
/**
     * Generate code to invoke the Class.forName with the name of the given
     * class to get its Class object at runtime.  The code is written to
     * the supplied stream.  Note that the code generated by this method
     * may cause the checked ClassNotFoundException to be thrown.
     */
    private void codeClassForName(Class<?> cl, DataOutputStream out)
        throws IOException
    {
        code_ldc(cp.getString(cl.getName()), out);

        out.writeByte(opc_invokestatic);
        out.writeShort(cp.getMethodRef(
            "java/lang/Class",
            "forName", "(Ljava/lang/String;)Ljava/lang/Class;"));
    }


    /*
     * ==================== General Utility Methods ====================
     */

    
Convert a fully qualified class name that uses '.' as the package
separator, the external representation used by the Java language
and APIs, to a fully qualified class name that uses '/' as the
package separator, the representation used in the class file
format (see JVMS section 4.2).
/**
     * Convert a fully qualified class name that uses '.' as the package
     * separator, the external representation used by the Java language
     * and APIs, to a fully qualified class name that uses '/' as the
     * package separator, the representation used in the class file
     * format (see JVMS section 4.2).
     */
    private static String dotToSlash(String name) {
        return name.replace('.', '/');
    }

    
Return the "method descriptor" string for a method with the given
parameter types and return type.  See JVMS section 4.3.3.
/**
     * Return the "method descriptor" string for a method with the given
     * parameter types and return type.  See JVMS section 4.3.3.
     */
    private static String getMethodDescriptor(Class<?>[] parameterTypes,
                                              Class<?> returnType)
    {
        return getParameterDescriptors(parameterTypes) +
            ((returnType == void.class) ? "V" : getFieldType(returnType));
    }

    
Return the list of "parameter descriptor" strings enclosed in
parentheses corresponding to the given parameter types (in other
words, a method descriptor without a return descriptor).  This
string is useful for constructing string keys for methods without
regard to their return type.
/**
     * Return the list of "parameter descriptor" strings enclosed in
     * parentheses corresponding to the given parameter types (in other
     * words, a method descriptor without a return descriptor).  This
     * string is useful for constructing string keys for methods without
     * regard to their return type.
     */
    private static String getParameterDescriptors(Class<?>[] parameterTypes) {
        StringBuilder desc = new StringBuilder("(");
        for (int i = 0; i < parameterTypes.length; i++) {
            desc.append(getFieldType(parameterTypes[i]));
        }
        desc.append(')');
        return desc.toString();
    }

    
Return the "field type" string for the given type, appropriate for
a field descriptor, a parameter descriptor, or a return descriptor
other than "void".  See JVMS section 4.3.2.
/**
     * Return the "field type" string for the given type, appropriate for
     * a field descriptor, a parameter descriptor, or a return descriptor
     * other than "void".  See JVMS section 4.3.2.
     */
    private static String getFieldType(Class<?> type) {
        if (type.isPrimitive()) {
            return PrimitiveTypeInfo.get(type).baseTypeString;
        } else if (type.isArray()) {
            /*
             * According to JLS 20.3.2, the getName() method on Class does
             * return the VM type descriptor format for array classes (only);
             * using that should be quicker than the otherwise obvious code:
             *
             *     return "[" + getTypeDescriptor(type.getComponentType());
             */
            return type.getName().replace('.', '/');
        } else {
            return "L" + dotToSlash(type.getName()) + ";";
        }
    }

    
Returns a human-readable string representing the signature of a
method with the given name and parameter types.
/**
     * Returns a human-readable string representing the signature of a
     * method with the given name and parameter types.
     */
    private static String getFriendlyMethodSignature(String name,
                                                     Class<?>[] parameterTypes)
    {
        StringBuilder sig = new StringBuilder(name);
        sig.append('(');
        for (int i = 0; i < parameterTypes.length; i++) {
            if (i > 0) {
                sig.append(',');
            }
            Class<?> parameterType = parameterTypes[i];
            int dimensions = 0;
            while (parameterType.isArray()) {
                parameterType = parameterType.getComponentType();
                dimensions++;
            }
            sig.append(parameterType.getName());
            while (dimensions-- > 0) {
                sig.append("[]");
            }
        }
        sig.append(')');
        return sig.toString();
    }

    
Return the number of abstract "words", or consecutive local variable
indexes, required to contain a value of the given type.  See JVMS
section 3.6.1.
Note that the original version of the JVMS contained a definition of
this abstract notion of a "word" in section 3.4, but that definition
was removed for the second edition.
/**
     * Return the number of abstract "words", or consecutive local variable
     * indexes, required to contain a value of the given type.  See JVMS
     * section 3.6.1.
     *
     * Note that the original version of the JVMS contained a definition of
     * this abstract notion of a "word" in section 3.4, but that definition
     * was removed for the second edition.
     */
    private static int getWordsPerType(Class<?> type) {
        if (type == long.class || type == double.class) {
            return 2;
        } else {
            return 1;
        }
    }

    
Add to the given list all of the types in the "from" array that
are not already contained in the list and are assignable to at
least one of the types in the "with" array.
This method is useful for computing the greatest common set of
declared exceptions from duplicate methods inherited from
different interfaces.
/**
     * Add to the given list all of the types in the "from" array that
     * are not already contained in the list and are assignable to at
     * least one of the types in the "with" array.
     *
     * This method is useful for computing the greatest common set of
     * declared exceptions from duplicate methods inherited from
     * different interfaces.
     */
    private static void collectCompatibleTypes(Class<?>[] from,
                                               Class<?>[] with,
                                               List<Class<?>> list)
    {
        for (Class<?> fc: from) {
            if (!list.contains(fc)) {
                for (Class<?> wc: with) {
                    if (wc.isAssignableFrom(fc)) {
                        list.add(fc);
                        break;
                    }
                }
            }
        }
    }

    
Given the exceptions declared in the throws clause of a proxy method,
compute the exceptions that need to be caught from the invocation
handler's invoke method and rethrown intact in the method's
implementation before catching other Throwables and wrapping them
in UndeclaredThrowableExceptions.
The exceptions to be caught are returned in a List object.  Each
exception in the returned list is guaranteed to not be a subclass of
any of the other exceptions in the list, so the catch blocks for
these exceptions may be generated in any order relative to each other.
Error and RuntimeException are each always contained by the returned
list (if none of their superclasses are contained), since those
unchecked exceptions should always be rethrown intact, and thus their
subclasses will never appear in the returned list.
The returned List will be empty if java.lang.Throwable is in the
given list of declared exceptions, indicating that no exceptions
need to be caught.
/**
     * Given the exceptions declared in the throws clause of a proxy method,
     * compute the exceptions that need to be caught from the invocation
     * handler's invoke method and rethrown intact in the method's
     * implementation before catching other Throwables and wrapping them
     * in UndeclaredThrowableExceptions.
     *
     * The exceptions to be caught are returned in a List object.  Each
     * exception in the returned list is guaranteed to not be a subclass of
     * any of the other exceptions in the list, so the catch blocks for
     * these exceptions may be generated in any order relative to each other.
     *
     * Error and RuntimeException are each always contained by the returned
     * list (if none of their superclasses are contained), since those
     * unchecked exceptions should always be rethrown intact, and thus their
     * subclasses will never appear in the returned list.
     *
     * The returned List will be empty if java.lang.Throwable is in the
     * given list of declared exceptions, indicating that no exceptions
     * need to be caught.
     */
    private static List<Class<?>> computeUniqueCatchList(Class<?>[] exceptions) {
        List<Class<?>> uniqueList = new ArrayList<>();
                                                // unique exceptions to catch

        uniqueList.add(Error.class);            // always catch/rethrow these
        uniqueList.add(RuntimeException.class);

    nextException:
        for (Class<?> ex: exceptions) {
            if (ex.isAssignableFrom(Throwable.class)) {
                /*
                 * If Throwable is declared to be thrown by the proxy method,
                 * then no catch blocks are necessary, because the invoke
                 * can, at most, throw Throwable anyway.
                 */
                uniqueList.clear();
                break;
            } else if (!Throwable.class.isAssignableFrom(ex)) {
                /*
                 * Ignore types that cannot be thrown by the invoke method.
                 */
                continue;
            }
            /*
             * Compare this exception against the current list of
             * exceptions that need to be caught:
             */
            for (int j = 0; j < uniqueList.size();) {
                Class<?> ex2 = uniqueList.get(j);
                if (ex2.isAssignableFrom(ex)) {
                    /*
                     * if a superclass of this exception is already on
                     * the list to catch, then ignore this one and continue;
                     */
                    continue nextException;
                } else if (ex.isAssignableFrom(ex2)) {
                    /*
                     * if a subclass of this exception is on the list
                     * to catch, then remove it;
                     */
                    uniqueList.remove(j);
                } else {
                    j++;        // else continue comparing.
                }
            }
            // This exception is unique (so far): add it to the list to catch.
            uniqueList.add(ex);
        }
        return uniqueList;
    }

    
A PrimitiveTypeInfo object contains assorted information about
a primitive type in its public fields.  The struct for a particular
primitive type can be obtained using the static "get" method.
/**
     * A PrimitiveTypeInfo object contains assorted information about
     * a primitive type in its public fields.  The struct for a particular
     * primitive type can be obtained using the static "get" method.
     */
    private static class PrimitiveTypeInfo {

        
"base type" used in various descriptors (see JVMS section 4.3.2) /** "base type" used in various descriptors (see JVMS section 4.3.2) */
        public String baseTypeString;

        
name of corresponding wrapper class /** name of corresponding wrapper class */
        public String wrapperClassName;

        
method descriptor for wrapper class "valueOf" factory method /** method descriptor for wrapper class "valueOf" factory method */
        public String wrapperValueOfDesc;

        
name of wrapper class method for retrieving primitive value /** name of wrapper class method for retrieving primitive value */
        public String unwrapMethodName;

        
descriptor of same method /** descriptor of same method */
        public String unwrapMethodDesc;

        private static Map<Class<?>,PrimitiveTypeInfo> table = new HashMap<>();
        static {
            add(byte.class, Byte.class);
            add(char.class, Character.class);
            add(double.class, Double.class);
            add(float.class, Float.class);
            add(int.class, Integer.class);
            add(long.class, Long.class);
            add(short.class, Short.class);
            add(boolean.class, Boolean.class);
        }

        private static void add(Class<?> primitiveClass, Class<?> wrapperClass) {
            table.put(primitiveClass,
                      new PrimitiveTypeInfo(primitiveClass, wrapperClass));
        }

        private PrimitiveTypeInfo(Class<?> primitiveClass, Class<?> wrapperClass) {
            assert primitiveClass.isPrimitive();

            baseTypeString =
                Array.newInstance(primitiveClass, 0)
                .getClass().getName().substring(1);
            wrapperClassName = dotToSlash(wrapperClass.getName());
            wrapperValueOfDesc =
                "(" + baseTypeString + ")L" + wrapperClassName + ";";
            unwrapMethodName = primitiveClass.getName() + "Value";
            unwrapMethodDesc = "()" + baseTypeString;
        }

        public static PrimitiveTypeInfo get(Class<?> cl) {
            return table.get(cl);
        }
    }


    
A ConstantPool object represents the constant pool of a class file
being generated.  This representation of a constant pool is designed
specifically for use by ProxyGenerator; in particular, it assumes
that constant pool entries will not need to be resorted (for example,
by their type, as the Java compiler does), so that the final index
value can be assigned and used when an entry is first created.
Note that new entries cannot be created after the constant pool has
been written to a class file.  To prevent such logic errors, a
ConstantPool instance can be marked "read only", so that further
attempts to add new entries will fail with a runtime exception.
See JVMS section 4.4 for more information about the constant pool
of a class file.
/**
     * A ConstantPool object represents the constant pool of a class file
     * being generated.  This representation of a constant pool is designed
     * specifically for use by ProxyGenerator; in particular, it assumes
     * that constant pool entries will not need to be resorted (for example,
     * by their type, as the Java compiler does), so that the final index
     * value can be assigned and used when an entry is first created.
     *
     * Note that new entries cannot be created after the constant pool has
     * been written to a class file.  To prevent such logic errors, a
     * ConstantPool instance can be marked "read only", so that further
     * attempts to add new entries will fail with a runtime exception.
     *
     * See JVMS section 4.4 for more information about the constant pool
     * of a class file.
     */
    private static class ConstantPool {

        
list of constant pool entries, in constant pool index order.
This list is used when writing the constant pool to a stream
and for assigning the next index value.  Note that element 0
of this list corresponds to constant pool index 1.
/**
         * list of constant pool entries, in constant pool index order.
         *
         * This list is used when writing the constant pool to a stream
         * and for assigning the next index value.  Note that element 0
         * of this list corresponds to constant pool index 1.
         */
        private List<Entry> pool = new ArrayList<>(32);

        
maps constant pool data of all types to constant pool indexes.
This map is used to look up the index of an existing entry for
values of all types.
/**
         * maps constant pool data of all types to constant pool indexes.
         *
         * This map is used to look up the index of an existing entry for
         * values of all types.
         */
        private Map<Object,Integer> map = new HashMap<>(16);

        
true if no new constant pool entries may be added /** true if no new constant pool entries may be added */
        private boolean readOnly = false;

        
Get or assign the index for a CONSTANT_Utf8 entry.
/**
         * Get or assign the index for a CONSTANT_Utf8 entry.
         */
        public short getUtf8(String s) {
            if (s == null) {
                throw new NullPointerException();
            }
            return getValue(s);
        }

        
Get or assign the index for a CONSTANT_Integer entry.
/**
         * Get or assign the index for a CONSTANT_Integer entry.
         */
        public short getInteger(int i) {
            return getValue(i);
        }

        
Get or assign the index for a CONSTANT_Float entry.
/**
         * Get or assign the index for a CONSTANT_Float entry.
         */
        public short getFloat(float f) {
            return getValue(f);
        }

        
Get or assign the index for a CONSTANT_Class entry.
/**
         * Get or assign the index for a CONSTANT_Class entry.
         */
        public short getClass(String name) {
            short utf8Index = getUtf8(name);
            return getIndirect(new IndirectEntry(
                CONSTANT_CLASS, utf8Index));
        }

        
Get or assign the index for a CONSTANT_String entry.
/**
         * Get or assign the index for a CONSTANT_String entry.
         */
        public short getString(String s) {
            short utf8Index = getUtf8(s);
            return getIndirect(new IndirectEntry(
                CONSTANT_STRING, utf8Index));
        }

        
Get or assign the index for a CONSTANT_FieldRef entry.
/**
         * Get or assign the index for a CONSTANT_FieldRef entry.
         */
        public short getFieldRef(String className,
                                 String name, String descriptor)
        {
            short classIndex = getClass(className);
            short nameAndTypeIndex = getNameAndType(name, descriptor);
            return getIndirect(new IndirectEntry(
                CONSTANT_FIELD, classIndex, nameAndTypeIndex));
        }

        
Get or assign the index for a CONSTANT_MethodRef entry.
/**
         * Get or assign the index for a CONSTANT_MethodRef entry.
         */
        public short getMethodRef(String className,
                                  String name, String descriptor)
        {
            short classIndex = getClass(className);
            short nameAndTypeIndex = getNameAndType(name, descriptor);
            return getIndirect(new IndirectEntry(
                CONSTANT_METHOD, classIndex, nameAndTypeIndex));
        }

        
Get or assign the index for a CONSTANT_InterfaceMethodRef entry.
/**
         * Get or assign the index for a CONSTANT_InterfaceMethodRef entry.
         */
        public short getInterfaceMethodRef(String className, String name,
                                           String descriptor)
        {
            short classIndex = getClass(className);
            short nameAndTypeIndex = getNameAndType(name, descriptor);
            return getIndirect(new IndirectEntry(
                CONSTANT_INTERFACEMETHOD, classIndex, nameAndTypeIndex));
        }

        
Get or assign the index for a CONSTANT_NameAndType entry.
/**
         * Get or assign the index for a CONSTANT_NameAndType entry.
         */
        public short getNameAndType(String name, String descriptor) {
            short nameIndex = getUtf8(name);
            short descriptorIndex = getUtf8(descriptor);
            return getIndirect(new IndirectEntry(
                CONSTANT_NAMEANDTYPE, nameIndex, descriptorIndex));
        }

        
Set this ConstantPool instance to be "read only".
After this method has been called, further requests to get
an index for a non-existent entry will cause an InternalError
to be thrown instead of creating of the entry.
/**
         * Set this ConstantPool instance to be "read only".
         *
         * After this method has been called, further requests to get
         * an index for a non-existent entry will cause an InternalError
         * to be thrown instead of creating of the entry.
         */
        public void setReadOnly() {
            readOnly = true;
        }

        
Write this constant pool to a stream as part of
the class file format.
This consists of writing the "constant_pool_count" and
"constant_pool[]" items of the "ClassFile" structure, as
described in JVMS section 4.1.
/**
         * Write this constant pool to a stream as part of
         * the class file format.
         *
         * This consists of writing the "constant_pool_count" and
         * "constant_pool[]" items of the "ClassFile" structure, as
         * described in JVMS section 4.1.
         */
        public void write(OutputStream out) throws IOException {
            DataOutputStream dataOut = new DataOutputStream(out);

            // constant_pool_count: number of entries plus one
            dataOut.writeShort(pool.size() + 1);

            for (Entry e : pool) {
                e.write(dataOut);
            }
        }

        
Add a new constant pool entry and return its index.
/**
         * Add a new constant pool entry and return its index.
         */
        private short addEntry(Entry entry) {
            pool.add(entry);
            /*
             * Note that this way of determining the index of the
             * added entry is wrong if this pool supports
             * CONSTANT_Long or CONSTANT_Double entries.
             */
            if (pool.size() >= 65535) {
                throw new IllegalArgumentException(
                    "constant pool size limit exceeded");
            }
            return (short) pool.size();
        }

        
Get or assign the index for an entry of a type that contains
a direct value.  The type of the given object determines the
type of the desired entry as follows:
     java.lang.String        CONSTANT_Utf8
     java.lang.Integer       CONSTANT_Integer
     java.lang.Float         CONSTANT_Float
     java.lang.Long          CONSTANT_Long
     java.lang.Double        CONSTANT_DOUBLE
/**
         * Get or assign the index for an entry of a type that contains
         * a direct value.  The type of the given object determines the
         * type of the desired entry as follows:
         *
         *      java.lang.String        CONSTANT_Utf8
         *      java.lang.Integer       CONSTANT_Integer
         *      java.lang.Float         CONSTANT_Float
         *      java.lang.Long          CONSTANT_Long
         *      java.lang.Double        CONSTANT_DOUBLE
         */
        private short getValue(Object key) {
            Integer index = map.get(key);
            if (index != null) {
                return index.shortValue();
            } else {
                if (readOnly) {
                    throw new InternalError(
                        "late constant pool addition: " + key);
                }
                short i = addEntry(new ValueEntry(key));
                map.put(key, (int)i);
                return i;
            }
        }

        
Get or assign the index for an entry of a type that contains
references to other constant pool entries.
/**
         * Get or assign the index for an entry of a type that contains
         * references to other constant pool entries.
         */
        private short getIndirect(IndirectEntry e) {
            Integer index = map.get(e);
            if (index != null) {
                return index.shortValue();
            } else {
                if (readOnly) {
                    throw new InternalError("late constant pool addition");
                }
                short i = addEntry(e);
                map.put(e, (int)i);
                return i;
            }
        }

        
Entry is the abstact superclass of all constant pool entry types
that can be stored in the "pool" list; its purpose is to define a
common method for writing constant pool entries to a class file.
/**
         * Entry is the abstact superclass of all constant pool entry types
         * that can be stored in the "pool" list; its purpose is to define a
         * common method for writing constant pool entries to a class file.
         */
        private abstract static class Entry {
            public abstract void write(DataOutputStream out)
                throws IOException;
        }

        
ValueEntry represents a constant pool entry of a type that
contains a direct value (see the comments for the "getValue"
method for a list of such types).
ValueEntry objects are not used as keys for their entries in the
Map "map", so no useful hashCode or equals methods are defined.
/**
         * ValueEntry represents a constant pool entry of a type that
         * contains a direct value (see the comments for the "getValue"
         * method for a list of such types).
         *
         * ValueEntry objects are not used as keys for their entries in the
         * Map "map", so no useful hashCode or equals methods are defined.
         */
        private static class ValueEntry extends Entry {
            private Object value;

            public ValueEntry(Object value) {
                this.value = value;
            }

            public void write(DataOutputStream out) throws IOException {
                if (value instanceof String) {
                    out.writeByte(CONSTANT_UTF8);
                    out.writeUTF((String) value);
                } else if (value instanceof Integer) {
                    out.writeByte(CONSTANT_INTEGER);
                    out.writeInt(((Integer) value).intValue());
                } else if (value instanceof Float) {
                    out.writeByte(CONSTANT_FLOAT);
                    out.writeFloat(((Float) value).floatValue());
                } else if (value instanceof Long) {
                    out.writeByte(CONSTANT_LONG);
                    out.writeLong(((Long) value).longValue());
                } else if (value instanceof Double) {
                    out.writeDouble(CONSTANT_DOUBLE);
                    out.writeDouble(((Double) value).doubleValue());
                } else {
                    throw new InternalError("bogus value entry: " + value);
                }
            }
        }

        
IndirectEntry represents a constant pool entry of a type that
references other constant pool entries, i.e., the following types:
     CONSTANT_Class, CONSTANT_String, CONSTANT_Fieldref,
     CONSTANT_Methodref, CONSTANT_InterfaceMethodref, and
     CONSTANT_NameAndType.
Each of these entry types contains either one or two indexes of
other constant pool entries.
IndirectEntry objects are used as the keys for their entries in
the Map "map", so the hashCode and equals methods are overridden
to allow matching.
/**
         * IndirectEntry represents a constant pool entry of a type that
         * references other constant pool entries, i.e., the following types:
         *
         *      CONSTANT_Class, CONSTANT_String, CONSTANT_Fieldref,
         *      CONSTANT_Methodref, CONSTANT_InterfaceMethodref, and
         *      CONSTANT_NameAndType.
         *
         * Each of these entry types contains either one or two indexes of
         * other constant pool entries.
         *
         * IndirectEntry objects are used as the keys for their entries in
         * the Map "map", so the hashCode and equals methods are overridden
         * to allow matching.
         */
        private static class IndirectEntry extends Entry {
            private int tag;
            private short index0;
            private short index1;

            
Construct an IndirectEntry for a constant pool entry type
that contains one index of another entry.
/**
             * Construct an IndirectEntry for a constant pool entry type
             * that contains one index of another entry.
             */
            public IndirectEntry(int tag, short index) {
                this.tag = tag;
                this.index0 = index;
                this.index1 = 0;
            }

            
Construct an IndirectEntry for a constant pool entry type
that contains two indexes for other entries.
/**
             * Construct an IndirectEntry for a constant pool entry type
             * that contains two indexes for other entries.
             */
            public IndirectEntry(int tag, short index0, short index1) {
                this.tag = tag;
                this.index0 = index0;
                this.index1 = index1;
            }

            public void write(DataOutputStream out) throws IOException {
                out.writeByte(tag);
                out.writeShort(index0);
                /*
                 * If this entry type contains two indexes, write
                 * out the second, too.
                 */
                if (tag == CONSTANT_FIELD ||
                    tag == CONSTANT_METHOD ||
                    tag == CONSTANT_INTERFACEMETHOD ||
                    tag == CONSTANT_NAMEANDTYPE)
                {
                    out.writeShort(index1);
                }
            }

            public int hashCode() {
                return tag + index0 + index1;
            }

            public boolean equals(Object obj) {
                if (obj instanceof IndirectEntry) {
                    IndirectEntry other = (IndirectEntry) obj;
                    if (tag == other.tag &&
                        index0 == other.index0 && index1 == other.index1)
                    {
                        return true;
                    }
                }
                return false;
            }
        }
    }
}