/*
- * Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2021, 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;
 
 import jdk.internal.loader.BuiltinClassLoader;
 import jdk.internal.misc.VM;
 import jdk.internal.module.ModuleHashes;
 import jdk.internal.module.ModuleReferenceImpl;
 
 import java.lang.module.ModuleDescriptor.Version;
 import java.lang.module.ModuleReference;
 import java.lang.module.ResolvedModule;
 import java.util.HashSet;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 
 /**
  * An element in a stack trace, as returned by {@link
  * Throwable#getStackTrace()}.  Each element represents a single stack frame.
  * All stack frames except for the one at the top of the stack represent
  * a method invocation.  The frame at the top of the stack represents the
  * execution point at which the stack trace was generated.  Typically,
  * this is the point at which the throwable corresponding to the stack trace
  * was created.
  *
  * @since  1.4
  * @author Josh Bloch
  */
 public final class StackTraceElement implements java.io.Serializable {
 
     // For Throwables and StackWalker, the VM initially sets this field to a
     // reference to the declaring Class.  The Class reference is used to
     // construct the 'format' bitmap, and then is cleared.
     //
     // For STEs constructed using the public constructors, this field is not used.
     private transient Class<?> declaringClassObject;
 
     // Normally initialized by VM
     /**
      * The name of the class loader.
      */
     private String classLoaderName;
     /**
      * The module name.
      */
     private String moduleName;
     /**
      * The module version.
      */
     private String moduleVersion;
     /**
      * The declaring class.
      */
     private String declaringClass;
     /**
      * The method name.
      */
     private String methodName;
     /**
      * The source file name.
      */
     private String fileName;
     /**
      * The source line number.
      */
     private int    lineNumber;
     /**
      * Control to show full or partial module, package, and class names.
      */
     private byte   format = 0; // Default to show all
 
     /**
      * Creates a stack trace element representing the specified execution
      * point. The {@link #getModuleName module name} and {@link
      * #getModuleVersion module version} of the stack trace element will
      * be {@code null}.
      *
      * @param declaringClass the fully qualified name of the class containing
      *        the execution point represented by the stack trace element
      * @param methodName the name of the method containing the execution point
      *        represented by the stack trace element
      * @param fileName the name of the file containing the execution point
      *         represented by the stack trace element, or {@code null} if
      *         this information is unavailable
      * @param lineNumber the line number of the source line containing the
      *         execution point represented by this stack trace element, or
      *         a negative number if this information is unavailable. A value
      *         of -2 indicates that the method containing the execution point
      *         is a native method
      * @throws NullPointerException if {@code declaringClass} or
      *         {@code methodName} is null
      * @since 1.5
      * @revised 9
      */
     public StackTraceElement(String declaringClass, String methodName,
                              String fileName, int lineNumber) {
         this(null, null, null, declaringClass, methodName, fileName, lineNumber);
     }
 
     /**
      * Creates a stack trace element representing the specified execution
      * point.
      *
      * @param classLoaderName the class loader name if the class loader of
      *        the class containing the execution point represented by
      *        the stack trace is named; otherwise {@code null}
      * @param moduleName the module name if the class containing the
      *        execution point represented by the stack trace is in a named
      *        module; otherwise {@code null}
      * @param moduleVersion the module version if the class containing the
      *        execution point represented by the stack trace is in a named
      *        module that has a version; otherwise {@code null}
      * @param declaringClass the fully qualified name of the class containing
      *        the execution point represented by the stack trace element
      * @param methodName the name of the method containing the execution point
      *        represented by the stack trace element
      * @param fileName the name of the file containing the execution point
      *        represented by the stack trace element, or {@code null} if
      *        this information is unavailable
      * @param lineNumber the line number of the source line containing the
      *        execution point represented by this stack trace element, or
      *        a negative number if this information is unavailable. A value
      *        of -2 indicates that the method containing the execution point
      *        is a native method
      *
      * @throws NullPointerException if {@code declaringClass} is {@code null}
      *         or {@code methodName} is {@code null}
      *
      * @since 9
      */
     public StackTraceElement(String classLoaderName,
                              String moduleName, String moduleVersion,
                              String declaringClass, String methodName,
                              String fileName, int lineNumber) {
         this.classLoaderName = classLoaderName;
         this.moduleName      = moduleName;
         this.moduleVersion   = moduleVersion;
         this.declaringClass  = Objects.requireNonNull(declaringClass, "Declaring class is null");
         this.methodName      = Objects.requireNonNull(methodName, "Method name is null");
         this.fileName        = fileName;
         this.lineNumber      = lineNumber;
     }
 
     /*
      * Private constructor for the factory methods to create StackTraceElement
      * for Throwable and StackFrameInfo
      */
     private StackTraceElement() {}
 
     /**
      * Returns the name of the source file containing the execution point
      * represented by this stack trace element.  Generally, this corresponds
      * to the {@code SourceFile} attribute of the relevant {@code class}
      * file (as per <cite>The Java Virtual Machine Specification</cite>, Section
      * {@jvms 4.7.7}).  In some systems, the name may refer to some source code unit
      * other than a file, such as an entry in source repository.
      *
      * @return the name of the file containing the execution point
      *         represented by this stack trace element, or {@code null} if
      *         this information is unavailable.
      */
     public String getFileName() {
         return fileName;
     }
 
     /**
      * Returns the line number of the source line containing the execution
      * point represented by this stack trace element.  Generally, this is
      * derived from the {@code LineNumberTable} attribute of the relevant
      * {@code class} file (as per <cite>The Java Virtual Machine
      * Specification</cite>, Section {@jvms 4.7.8}).
      *
      * @return the line number of the source line containing the execution
      *         point represented by this stack trace element, or a negative
      *         number if this information is unavailable.
      */
     public int getLineNumber() {
         return lineNumber;
     }
 
     /**
      * Returns the module name of the module containing the execution point
      * represented by this stack trace element.
      *
      * @return the module name of the {@code Module} containing the execution
      *         point represented by this stack trace element; {@code null}
      *         if the module name is not available.
      * @since 9
      * @see Module#getName()
      */
     public String getModuleName() {
         return moduleName;
     }
 
     /**
      * Returns the module version of the module containing the execution point
      * represented by this stack trace element.
      *
      * @return the module version of the {@code Module} containing the execution
      *         point represented by this stack trace element; {@code null}
      *         if the module version is not available.
      * @since 9
      * @see java.lang.module.ModuleDescriptor.Version
      */
     public String getModuleVersion() {
         return moduleVersion;
     }
 
     /**
      * Returns the name of the class loader of the class containing the
      * execution point represented by this stack trace element.
      *
      * @return the name of the class loader of the class containing the execution
      *         point represented by this stack trace element; {@code null}
      *         if the class loader is not named.
      *
      * @since 9
      * @see java.lang.ClassLoader#getName()
      */
     public String getClassLoaderName() {
         return classLoaderName;
     }
 
     /**
      * Returns the fully qualified name of the class containing the
      * execution point represented by this stack trace element.
      *
      * @return the fully qualified name of the {@code Class} containing
      *         the execution point represented by this stack trace element.
      */
     public String getClassName() {
         return declaringClass;
     }
 
     /**
      * Returns the name of the method containing the execution point
      * represented by this stack trace element.  If the execution point is
      * contained in an instance or class initializer, this method will return
      * the appropriate <i>special method name</i>, {@code <init>} or
      * {@code <clinit>}, as per Section {@jvms 3.9} of <cite>The Java Virtual
      * Machine Specification</cite>.
      *
      * @return the name of the method containing the execution point
      *         represented by this stack trace element.
      */
     public String getMethodName() {
         return methodName;
     }
 
     /**
      * Returns true if the method containing the execution point
      * represented by this stack trace element is a native method.
      *
      * @return {@code true} if the method containing the execution point
      *         represented by this stack trace element is a native method.
      */
     public boolean isNativeMethod() {
         return lineNumber == -2;
     }
 
     /**
      * Returns a string representation of this stack trace element.
      *
      * @apiNote The format of this string depends on the implementation, but the
      * following examples may be regarded as typical:
      * <ul>
      * <li>
      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java:101)}"
      * - See the description below.
      * </li>
      * <li>
      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java)}"
      * - The line number is unavailable.
      * </li>
      * <li>
      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Unknown Source)}"
      * - Neither the file name nor the line number is available.
      * </li>
      * <li>
      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Native Method)}"
      * - The method containing the execution point is a native method.
      * </li>
      * <li>
      *     "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}"
      * - The class of the execution point is defined in the unnamed module of
      * the class loader named {@code com.foo.loader}.
      * </li>
      * <li>
      *     "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}"
      * - The class of the execution point is defined in {@code acme} module
      * loaded by a built-in class loader such as the application class loader.
      * </li>
      * <li>
      *     "{@code MyClass.mash(MyClass.java:9)}"
      * - {@code MyClass} class is on the application class path.
      * </li>
      * </ul>
      *
      * <p> The first example shows a stack trace element consisting of
      * three elements, each separated by {@code "/"}, followed by
      * the source file name and the line number of the source line
      * containing the execution point.
      *
      * The first element "{@code com.foo.loader}" is
      * the name of the class loader.  The second element "{@code foo@9.0}"
      * is the module name and version.  The third element is the method
      * containing the execution point; "{@code com.foo.Main"}" is the
      * fully-qualified class name and "{@code run}" is the name of the method.
      * "{@code Main.java}" is the source file name and "{@code 101}" is
      * the line number.
      *
      * <p> If a class is defined in an <em>unnamed module</em>
      * then the second element is omitted as shown in
      * "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}".
      *
      * <p> If the class loader is a <a href="ClassLoader.html#builtinLoaders">
      * built-in class loader</a> or is not named then the first element
      * and its following {@code "/"} are omitted as shown in
      * "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}".
      * If the first element is omitted and the module is an unnamed module,
      * the second element and its following {@code "/"} are also omitted
      * as shown in "{@code MyClass.mash(MyClass.java:9)}".
      *
      * <p> The {@code toString} method may return two different values on two
      * {@code StackTraceElement} instances that are
      * {@linkplain #equals(Object) equal}, for example one created via the
      * constructor, and one obtained from {@link java.lang.Throwable} or
      * {@link java.lang.StackWalker.StackFrame}, where an implementation may
      * choose to omit some element in the returned string.
      *
      * @revised 9
      * @see    Throwable#printStackTrace()
      */
     public String toString() {
         String s = "";
         if (!dropClassLoaderName() && classLoaderName != null &&
                 !classLoaderName.isEmpty()) {
             s += classLoaderName + "/";
         }
         if (moduleName != null && !moduleName.isEmpty()) {
             s += moduleName;
 
             if (!dropModuleVersion() && moduleVersion != null &&
                     !moduleVersion.isEmpty()) {
                 s += "@" + moduleVersion;
             }
         }
         s = s.isEmpty() ? declaringClass : s + "/" + declaringClass;
 
         return s + "." + methodName + "(" +
              (isNativeMethod() ? "Native Method)" :
               (fileName != null && lineNumber >= 0 ?
                fileName + ":" + lineNumber + ")" :
                 (fileName != null ?  ""+fileName+")" : "Unknown Source)")));
     }
 
     /**
      * Returns true if the specified object is another
      * {@code StackTraceElement} instance representing the same execution
      * point as this instance.  Two stack trace elements {@code a} and
      * {@code b} are equal if and only if:
      * <pre>{@code
      *     equals(a.getClassLoaderName(), b.getClassLoaderName()) &&
      *     equals(a.getModuleName(), b.getModuleName()) &&
      *     equals(a.getModuleVersion(), b.getModuleVersion()) &&
      *     equals(a.getClassName(), b.getClassName()) &&
      *     equals(a.getMethodName(), b.getMethodName())
      *     equals(a.getFileName(), b.getFileName()) &&
      *     a.getLineNumber() == b.getLineNumber()
      *
      * }</pre>
      * where {@code equals} has the semantics of {@link
      * java.util.Objects#equals(Object, Object) Objects.equals}.
      *
      * @param  obj the object to be compared with this stack trace element.
      * @return true if the specified object is another
      *         {@code StackTraceElement} instance representing the same
      *         execution point as this instance.
      *
      * @revised 9
      */
     public boolean equals(Object obj) {
         if (obj==this)
             return true;
-        if (!(obj instanceof StackTraceElement))
-            return false;
-        StackTraceElement e = (StackTraceElement)obj;
-        return Objects.equals(classLoaderName, e.classLoaderName) &&
-            Objects.equals(moduleName, e.moduleName) &&
-            Objects.equals(moduleVersion, e.moduleVersion) &&
-            e.declaringClass.equals(declaringClass) &&
-            e.lineNumber == lineNumber &&
-            Objects.equals(methodName, e.methodName) &&
-            Objects.equals(fileName, e.fileName);
+        return (obj instanceof StackTraceElement e)
+                && e.lineNumber == lineNumber
+                && e.declaringClass.equals(declaringClass)
+                && Objects.equals(classLoaderName, e.classLoaderName)
+                && Objects.equals(moduleName, e.moduleName)
+                && Objects.equals(moduleVersion, e.moduleVersion)
+                && Objects.equals(methodName, e.methodName)
+                && Objects.equals(fileName, e.fileName);
     }
 
     /**
      * Returns a hash code value for this stack trace element.
      */
     public int hashCode() {
         int result = 31*declaringClass.hashCode() + methodName.hashCode();
         result = 31*result + Objects.hashCode(classLoaderName);
         result = 31*result + Objects.hashCode(moduleName);
         result = 31*result + Objects.hashCode(moduleVersion);
         result = 31*result + Objects.hashCode(fileName);
         result = 31*result + lineNumber;
         return result;
     }
 
 
     /**
      * Called from of() methods to set the 'format' bitmap using the Class
      * reference stored in declaringClassObject, and then clear the reference.
      *
      * <p>
      * If the module is a non-upgradeable JDK module, then set
      * JDK_NON_UPGRADEABLE_MODULE to omit its version string.
      * <p>
      * If the loader is one of the built-in loaders (`boot`, `platform`, or `app`)
      * then set BUILTIN_CLASS_LOADER to omit the first element (`<loader>/`).
      */
     private synchronized void computeFormat() {
         try {
-            Class<?> cls = (Class<?>) declaringClassObject;
+            Class<?> cls = declaringClassObject;
             ClassLoader loader = cls.getClassLoader0();
             Module m = cls.getModule();
             byte bits = 0;
 
             // First element - class loader name
             // Call package-private ClassLoader::name method
 
             if (loader instanceof BuiltinClassLoader) {
                 bits |= BUILTIN_CLASS_LOADER;
             }
 
             // Second element - module name and version
 
             // Omit if is a JDK non-upgradeable module (recorded in the hashes
             // in java.base)
             if (isHashedInJavaBase(m)) {
                 bits |= JDK_NON_UPGRADEABLE_MODULE;
             }
             format = bits;
         } finally {
             // Class reference no longer needed, clear it
             declaringClassObject = null;
         }
     }
 
     private static final byte BUILTIN_CLASS_LOADER       = 0x1;
     private static final byte JDK_NON_UPGRADEABLE_MODULE = 0x2;
 
     private boolean dropClassLoaderName() {
         return (format & BUILTIN_CLASS_LOADER) == BUILTIN_CLASS_LOADER;
     }
 
     private boolean dropModuleVersion() {
         return (format & JDK_NON_UPGRADEABLE_MODULE) == JDK_NON_UPGRADEABLE_MODULE;
     }
 
     /**
      * Returns true if the module is hashed with java.base.
      * <p>
      * This method returns false when running on the exploded image
      * since JDK modules are not hashed. They have no Version attribute
      * and so "@<version>" part will be omitted anyway.
      */
     private static boolean isHashedInJavaBase(Module m) {
         // return true if module system is not initialized as the code
         // must be in java.base
         if (!VM.isModuleSystemInited())
             return true;
 
         return ModuleLayer.boot() == m.getLayer() && HashedModules.contains(m);
     }
 
     /*
      * Finds JDK non-upgradeable modules, i.e. the modules that are
      * included in the hashes in java.base.
      */
     private static class HashedModules {
         static Set<String> HASHED_MODULES = hashedModules();
 
         static Set<String> hashedModules() {
 
             Optional<ResolvedModule> resolvedModule = ModuleLayer.boot()
                     .configuration()
                     .findModule("java.base");
             assert resolvedModule.isPresent();
             ModuleReference mref = resolvedModule.get().reference();
             assert mref instanceof ModuleReferenceImpl;
             ModuleHashes hashes = ((ModuleReferenceImpl)mref).recordedHashes();
             if (hashes != null) {
                 Set<String> names = new HashSet<>(hashes.names());
                 names.add("java.base");
                 return names;
             }
 
             return Set.of();
         }
 
         static boolean contains(Module m) {
             return HASHED_MODULES.contains(m.getName());
         }
     }
 
 
     /*
      * Returns an array of StackTraceElements of the given depth
      * filled from the backtrace of a given Throwable.
      */
     static StackTraceElement[] of(Throwable x, int depth) {
         StackTraceElement[] stackTrace = new StackTraceElement[depth];
         for (int i = 0; i < depth; i++) {
             stackTrace[i] = new StackTraceElement();
         }
 
         // VM to fill in StackTraceElement
         initStackTraceElements(stackTrace, x);
 
         // ensure the proper StackTraceElement initialization
         for (StackTraceElement ste : stackTrace) {
             ste.computeFormat();
         }
         return stackTrace;
     }
 
     /*
      * Returns a StackTraceElement from a given StackFrameInfo.
      */
     static StackTraceElement of(StackFrameInfo sfi) {
         StackTraceElement ste = new StackTraceElement();
         initStackTraceElement(ste, sfi);
 
         ste.computeFormat();
         return ste;
     }
 
     /*
      * Sets the given stack trace elements with the backtrace
      * of the given Throwable.
      */
     private static native void initStackTraceElements(StackTraceElement[] elements,
                                                       Throwable x);
     /*
      * Sets the given stack trace element with the given StackFrameInfo
      */
     private static native void initStackTraceElement(StackTraceElement element,
                                                      StackFrameInfo sfi);
 
     @java.io.Serial
     private static final long serialVersionUID = 6992337162326171013L;
 }