src/share/classes/java/lang/Object.java

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rev 814 : 6239194: Object.hashCode() should reference System.identityHashCode()
Reviewed-by: emcmanus

@@ -24,12 +24,12 @@
  */
 
 package java.lang;
 
 /**
- * Class <code>Object</code> is the root of the class hierarchy.
- * Every class has <code>Object</code> as a superclass. All objects,
+ * Class {@code Object} is the root of the class hierarchy.
+ * Every class has {@code Object} as a superclass. All objects,
  * including arrays, implement the methods of this class.
  *
  * @author  unascribed
  * @see     java.lang.Class
  * @since   JDK1.0

@@ -64,166 +64,166 @@
      */
     public final native Class<?> getClass();
 
     /**
      * Returns a hash code value for the object. This method is
-     * supported for the benefit of hashtables such as those provided by
-     * <code>java.util.Hashtable</code>.
+     * supported for the benefit of hash tables such as those provided by
+     * {@link java.util.HashMap}.
      * <p>
-     * The general contract of <code>hashCode</code> is:
+     * The general contract of {@code hashCode} is:
      * <ul>
      * <li>Whenever it is invoked on the same object more than once during
-     *     an execution of a Java application, the <tt>hashCode</tt> method
+     *     an execution of a Java application, the {@code hashCode} method
      *     must consistently return the same integer, provided no information
-     *     used in <tt>equals</tt> comparisons on the object is modified.
+     *     used in {@code equals} comparisons on the object is modified.
      *     This integer need not remain consistent from one execution of an
      *     application to another execution of the same application.
-     * <li>If two objects are equal according to the <tt>equals(Object)</tt>
-     *     method, then calling the <code>hashCode</code> method on each of
+     * <li>If two objects are equal according to the {@code equals(Object)}
+     *     method, then calling the {@code hashCode} method on each of
      *     the two objects must produce the same integer result.
      * <li>It is <em>not</em> required that if two objects are unequal
      *     according to the {@link java.lang.Object#equals(java.lang.Object)}
-     *     method, then calling the <tt>hashCode</tt> method on each of the
+     *     method, then calling the {@code hashCode} method on each of the
      *     two objects must produce distinct integer results.  However, the
      *     programmer should be aware that producing distinct integer results
-     *     for unequal objects may improve the performance of hashtables.
+     *     for unequal objects may improve the performance of hash tables.
      * </ul>
      * <p>
      * As much as is reasonably practical, the hashCode method defined by
-     * class <tt>Object</tt> does return distinct integers for distinct
+     * class {@code Object} does return distinct integers for distinct
      * objects. (This is typically implemented by converting the internal
      * address of the object into an integer, but this implementation
      * technique is not required by the
      * Java<font size="-2"><sup>TM</sup></font> programming language.)
      *
      * @return  a hash code value for this object.
      * @see     java.lang.Object#equals(java.lang.Object)
-     * @see     java.util.Hashtable
+     * @see     java.lang.System#identityHashCode
      */
     public native int hashCode();
 
     /**
      * Indicates whether some other object is "equal to" this one.
      * <p>
-     * The <code>equals</code> method implements an equivalence relation
+     * The {@code equals} method implements an equivalence relation
      * on non-null object references:
      * <ul>
      * <li>It is <i>reflexive</i>: for any non-null reference value
-     *     <code>x</code>, <code>x.equals(x)</code> should return
-     *     <code>true</code>.
+     *     {@code x}, {@code x.equals(x)} should return
+     *     {@code true}.
      * <li>It is <i>symmetric</i>: for any non-null reference values
-     *     <code>x</code> and <code>y</code>, <code>x.equals(y)</code>
-     *     should return <code>true</code> if and only if
-     *     <code>y.equals(x)</code> returns <code>true</code>.
+     *     {@code x} and {@code y}, {@code x.equals(y)}
+     *     should return {@code true} if and only if
+     *     {@code y.equals(x)} returns {@code true}.
      * <li>It is <i>transitive</i>: for any non-null reference values
-     *     <code>x</code>, <code>y</code>, and <code>z</code>, if
-     *     <code>x.equals(y)</code> returns <code>true</code> and
-     *     <code>y.equals(z)</code> returns <code>true</code>, then
-     *     <code>x.equals(z)</code> should return <code>true</code>.
+     *     {@code x}, {@code y}, and {@code z}, if
+     *     {@code x.equals(y)} returns {@code true} and
+     *     {@code y.equals(z)} returns {@code true}, then
+     *     {@code x.equals(z)} should return {@code true}.
      * <li>It is <i>consistent</i>: for any non-null reference values
-     *     <code>x</code> and <code>y</code>, multiple invocations of
-     *     <tt>x.equals(y)</tt> consistently return <code>true</code>
-     *     or consistently return <code>false</code>, provided no
-     *     information used in <code>equals</code> comparisons on the
+     *     {@code x} and {@code y}, multiple invocations of
+     *     {@code x.equals(y)} consistently return {@code true}
+     *     or consistently return {@code false}, provided no
+     *     information used in {@code equals} comparisons on the
      *     objects is modified.
-     * <li>For any non-null reference value <code>x</code>,
-     *     <code>x.equals(null)</code> should return <code>false</code>.
+     * <li>For any non-null reference value {@code x},
+     *     {@code x.equals(null)} should return {@code false}.
      * </ul>
      * <p>
-     * The <tt>equals</tt> method for class <code>Object</code> implements
+     * The {@code equals} method for class {@code Object} implements
      * the most discriminating possible equivalence relation on objects;
-     * that is, for any non-null reference values <code>x</code> and
-     * <code>y</code>, this method returns <code>true</code> if and only
-     * if <code>x</code> and <code>y</code> refer to the same object
-     * (<code>x == y</code> has the value <code>true</code>).
+     * that is, for any non-null reference values {@code x} and
+     * {@code y}, this method returns {@code true} if and only
+     * if {@code x} and {@code y} refer to the same object
+     * ({@code x == y} has the value {@code true}).
      * <p>
-     * Note that it is generally necessary to override the <tt>hashCode</tt>
+     * Note that it is generally necessary to override the {@code hashCode}
      * method whenever this method is overridden, so as to maintain the
-     * general contract for the <tt>hashCode</tt> method, which states
+     * general contract for the {@code hashCode} method, which states
      * that equal objects must have equal hash codes.
      *
      * @param   obj   the reference object with which to compare.
-     * @return  <code>true</code> if this object is the same as the obj
-     *          argument; <code>false</code> otherwise.
+     * @return  {@code true} if this object is the same as the obj
+     *          argument; {@code false} otherwise.
      * @see     #hashCode()
-     * @see     java.util.Hashtable
+     * @see     java.util.HashMap
      */
     public boolean equals(Object obj) {
         return (this == obj);
     }
 
     /**
      * Creates and returns a copy of this object.  The precise meaning
      * of "copy" may depend on the class of the object. The general
-     * intent is that, for any object <tt>x</tt>, the expression:
+     * intent is that, for any object {@code x}, the expression:
      * <blockquote>
      * <pre>
      * x.clone() != x</pre></blockquote>
      * will be true, and that the expression:
      * <blockquote>
      * <pre>
      * x.clone().getClass() == x.getClass()</pre></blockquote>
-     * will be <tt>true</tt>, but these are not absolute requirements.
+     * will be {@code true}, but these are not absolute requirements.
      * While it is typically the case that:
      * <blockquote>
      * <pre>
      * x.clone().equals(x)</pre></blockquote>
-     * will be <tt>true</tt>, this is not an absolute requirement.
+     * will be {@code true}, this is not an absolute requirement.
      * <p>
      * By convention, the returned object should be obtained by calling
-     * <tt>super.clone</tt>.  If a class and all of its superclasses (except
-     * <tt>Object</tt>) obey this convention, it will be the case that
-     * <tt>x.clone().getClass() == x.getClass()</tt>.
+     * {@code super.clone}.  If a class and all of its superclasses (except
+     * {@code Object}) obey this convention, it will be the case that
+     * {@code x.clone().getClass() == x.getClass()}.
      * <p>
      * By convention, the object returned by this method should be independent
      * of this object (which is being cloned).  To achieve this independence,
      * it may be necessary to modify one or more fields of the object returned
-     * by <tt>super.clone</tt> before returning it.  Typically, this means
+     * by {@code super.clone} before returning it.  Typically, this means
      * copying any mutable objects that comprise the internal "deep structure"
      * of the object being cloned and replacing the references to these
      * objects with references to the copies.  If a class contains only
      * primitive fields or references to immutable objects, then it is usually
-     * the case that no fields in the object returned by <tt>super.clone</tt>
+     * the case that no fields in the object returned by {@code super.clone}
      * need to be modified.
      * <p>
-     * The method <tt>clone</tt> for class <tt>Object</tt> performs a
+     * The method {@code clone} for class {@code Object} performs a
      * specific cloning operation. First, if the class of this object does
-     * not implement the interface <tt>Cloneable</tt>, then a
-     * <tt>CloneNotSupportedException</tt> is thrown. Note that all arrays
-     * are considered to implement the interface <tt>Cloneable</tt>.
+     * not implement the interface {@code Cloneable}, then a
+     * {@code CloneNotSupportedException} is thrown. Note that all arrays
+     * are considered to implement the interface {@code Cloneable}.
      * Otherwise, this method creates a new instance of the class of this
      * object and initializes all its fields with exactly the contents of
      * the corresponding fields of this object, as if by assignment; the
      * contents of the fields are not themselves cloned. Thus, this method
      * performs a "shallow copy" of this object, not a "deep copy" operation.
      * <p>
-     * The class <tt>Object</tt> does not itself implement the interface
-     * <tt>Cloneable</tt>, so calling the <tt>clone</tt> method on an object
-     * whose class is <tt>Object</tt> will result in throwing an
+     * The class {@code Object} does not itself implement the interface
+     * {@code Cloneable}, so calling the {@code clone} method on an object
+     * whose class is {@code Object} will result in throwing an
      * exception at run time.
      *
      * @return     a clone of this instance.
      * @exception  CloneNotSupportedException  if the object's class does not
-     *               support the <code>Cloneable</code> interface. Subclasses
-     *               that override the <code>clone</code> method can also
+     *               support the {@code Cloneable} interface. Subclasses
+     *               that override the {@code clone} method can also
      *               throw this exception to indicate that an instance cannot
      *               be cloned.
      * @see java.lang.Cloneable
      */
     protected native Object clone() throws CloneNotSupportedException;
 
     /**
      * Returns a string representation of the object. In general, the
-     * <code>toString</code> method returns a string that
+     * {@code toString} method returns a string that
      * "textually represents" this object. The result should
      * be a concise but informative representation that is easy for a
      * person to read.
      * It is recommended that all subclasses override this method.
      * <p>
-     * The <code>toString</code> method for class <code>Object</code>
+     * The {@code toString} method for class {@code Object}
      * returns a string consisting of the name of the class of which the
-     * object is an instance, the at-sign character `<code>@</code>', and
+     * object is an instance, the at-sign character `{@code @}', and
      * the unsigned hexadecimal representation of the hash code of the
      * object. In other words, this method returns a string equal to the
      * value of:
      * <blockquote>
      * <pre>

@@ -239,11 +239,11 @@
     /**
      * Wakes up a single thread that is waiting on this object's
      * monitor. If any threads are waiting on this object, one of them
      * is chosen to be awakened. The choice is arbitrary and occurs at
      * the discretion of the implementation. A thread waits on an object's
-     * monitor by calling one of the <code>wait</code> methods.
+     * monitor by calling one of the {@code wait} methods.
      * <p>
      * The awakened thread will not be able to proceed until the current
      * thread relinquishes the lock on this object. The awakened thread will
      * compete in the usual manner with any other threads that might be
      * actively competing to synchronize on this object; for example, the

@@ -253,13 +253,13 @@
      * This method should only be called by a thread that is the owner
      * of this object's monitor. A thread becomes the owner of the
      * object's monitor in one of three ways:
      * <ul>
      * <li>By executing a synchronized instance method of that object.
-     * <li>By executing the body of a <code>synchronized</code> statement
+     * <li>By executing the body of a {@code synchronized} statement
      *     that synchronizes on the object.
-     * <li>For objects of type <code>Class,</code> by executing a
+     * <li>For objects of type {@code Class,} by executing a
      *     synchronized static method of that class.
      * </ul>
      * <p>
      * Only one thread at a time can own an object's monitor.
      *

@@ -271,21 +271,21 @@
     public final native void notify();
 
     /**
      * Wakes up all threads that are waiting on this object's monitor. A
      * thread waits on an object's monitor by calling one of the
-     * <code>wait</code> methods.
+     * {@code wait} methods.
      * <p>
      * The awakened threads will not be able to proceed until the current
      * thread relinquishes the lock on this object. The awakened threads
      * will compete in the usual manner with any other threads that might
      * be actively competing to synchronize on this object; for example,
      * the awakened threads enjoy no reliable privilege or disadvantage in
      * being the next thread to lock this object.
      * <p>
      * This method should only be called by a thread that is the owner
-     * of this object's monitor. See the <code>notify</code> method for a
+     * of this object's monitor. See the {@code notify} method for a
      * description of the ways in which a thread can become the owner of
      * a monitor.
      *
      * @exception  IllegalMonitorStateException  if the current thread is not
      *               the owner of this object's monitor.

@@ -306,31 +306,31 @@
      * place itself in the wait set for this object and then to relinquish
      * any and all synchronization claims on this object. Thread <var>T</var>
      * becomes disabled for thread scheduling purposes and lies dormant
      * until one of four things happens:
      * <ul>
-     * <li>Some other thread invokes the <tt>notify</tt> method for this
+     * <li>Some other thread invokes the {@code notify} method for this
      * object and thread <var>T</var> happens to be arbitrarily chosen as
      * the thread to be awakened.
-     * <li>Some other thread invokes the <tt>notifyAll</tt> method for this
+     * <li>Some other thread invokes the {@code notifyAll} method for this
      * object.
      * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
      * thread <var>T</var>.
      * <li>The specified amount of real time has elapsed, more or less.  If
-     * <tt>timeout</tt> is zero, however, then real time is not taken into
+     * {@code timeout} is zero, however, then real time is not taken into
      * consideration and the thread simply waits until notified.
      * </ul>
      * The thread <var>T</var> is then removed from the wait set for this
      * object and re-enabled for thread scheduling. It then competes in the
      * usual manner with other threads for the right to synchronize on the
      * object; once it has gained control of the object, all its
      * synchronization claims on the object are restored to the status quo
-     * ante - that is, to the situation as of the time that the <tt>wait</tt>
+     * ante - that is, to the situation as of the time that the {@code wait}
      * method was invoked. Thread <var>T</var> then returns from the
-     * invocation of the <tt>wait</tt> method. Thus, on return from the
-     * <tt>wait</tt> method, the synchronization state of the object and of
-     * thread <tt>T</tt> is exactly as it was when the <tt>wait</tt> method
+     * invocation of the {@code wait} method. Thus, on return from the
+     * {@code wait} method, the synchronization state of the object and of
+     * thread {@code T} is exactly as it was when the {@code wait} method
      * was invoked.
      * <p>
      * A thread can also wake up without being notified, interrupted, or
      * timing out, a so-called <i>spurious wakeup</i>.  While this will rarely
      * occur in practice, applications must guard against it by testing for

@@ -349,22 +349,22 @@
      * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming
      * Language Guide" (Addison-Wesley, 2001).
      *
      * <p>If the current thread is {@linkplain java.lang.Thread#interrupt()
      * interrupted} by any thread before or while it is waiting, then an
-     * <tt>InterruptedException</tt> is thrown.  This exception is not
+     * {@code InterruptedException} is thrown.  This exception is not
      * thrown until the lock status of this object has been restored as
      * described above.
      *
      * <p>
-     * Note that the <tt>wait</tt> method, as it places the current thread
+     * Note that the {@code wait} method, as it places the current thread
      * into the wait set for this object, unlocks only this object; any
      * other objects on which the current thread may be synchronized remain
      * locked while the thread waits.
      * <p>
      * This method should only be called by a thread that is the owner
-     * of this object's monitor. See the <code>notify</code> method for a
+     * of this object's monitor. See the {@code notify} method for a
      * description of the ways in which a thread can become the owner of
      * a monitor.
      *
      * @param      timeout   the maximum time to wait in milliseconds.
      * @exception  IllegalArgumentException      if the value of timeout is

@@ -386,31 +386,31 @@
      * {@link java.lang.Object#notify()} method or the
      * {@link java.lang.Object#notifyAll()} method for this object, or
      * some other thread interrupts the current thread, or a certain
      * amount of real time has elapsed.
      * <p>
-     * This method is similar to the <code>wait</code> method of one
+     * This method is similar to the {@code wait} method of one
      * argument, but it allows finer control over the amount of time to
      * wait for a notification before giving up. The amount of real time,
      * measured in nanoseconds, is given by:
      * <blockquote>
      * <pre>
      * 1000000*timeout+nanos</pre></blockquote>
      * <p>
      * In all other respects, this method does the same thing as the
      * method {@link #wait(long)} of one argument. In particular,
-     * <tt>wait(0, 0)</tt> means the same thing as <tt>wait(0)</tt>.
+     * {@code wait(0, 0)} means the same thing as {@code wait(0)}.
      * <p>
      * The current thread must own this object's monitor. The thread
      * releases ownership of this monitor and waits until either of the
      * following two conditions has occurred:
      * <ul>
      * <li>Another thread notifies threads waiting on this object's monitor
-     *     to wake up either through a call to the <code>notify</code> method
-     *     or the <code>notifyAll</code> method.
-     * <li>The timeout period, specified by <code>timeout</code>
-     *     milliseconds plus <code>nanos</code> nanoseconds arguments, has
+     *     to wake up either through a call to the {@code notify} method
+     *     or the {@code notifyAll} method.
+     * <li>The timeout period, specified by {@code timeout}
+     *     milliseconds plus {@code nanos} nanoseconds arguments, has
      *     elapsed.
      * </ul>
      * <p>
      * The thread then waits until it can re-obtain ownership of the
      * monitor and resumes execution.

@@ -423,11 +423,11 @@
      *             obj.wait(timeout, nanos);
      *         ... // Perform action appropriate to condition
      *     }
      * </pre>
      * This method should only be called by a thread that is the owner
-     * of this object's monitor. See the <code>notify</code> method for a
+     * of this object's monitor. See the {@code notify} method for a
      * description of the ways in which a thread can become the owner of
      * a monitor.
      *
      * @param      timeout   the maximum time to wait in milliseconds.
      * @param      nanos      additional time, in nanoseconds range

@@ -463,17 +463,17 @@
     /**
      * Causes the current thread to wait until another thread invokes the
      * {@link java.lang.Object#notify()} method or the
      * {@link java.lang.Object#notifyAll()} method for this object.
      * In other words, this method behaves exactly as if it simply
-     * performs the call <tt>wait(0)</tt>.
+     * performs the call {@code wait(0)}.
      * <p>
      * The current thread must own this object's monitor. The thread
      * releases ownership of this monitor and waits until another thread
      * notifies threads waiting on this object's monitor to wake up
-     * either through a call to the <code>notify</code> method or the
-     * <code>notifyAll</code> method. The thread then waits until it can
+     * either through a call to the {@code notify} method or the
+     * {@code notifyAll} method. The thread then waits until it can
      * re-obtain ownership of the monitor and resumes execution.
      * <p>
      * As in the one argument version, interrupts and spurious wakeups are
      * possible, and this method should always be used in a loop:
      * <pre>

@@ -482,11 +482,11 @@
      *             obj.wait();
      *         ... // Perform action appropriate to condition
      *     }
      * </pre>
      * This method should only be called by a thread that is the owner
-     * of this object's monitor. See the <code>notify</code> method for a
+     * of this object's monitor. See the {@code notify} method for a
      * description of the ways in which a thread can become the owner of
      * a monitor.
      *
      * @exception  IllegalMonitorStateException  if the current thread is not
      *               the owner of the object's monitor.

@@ -503,51 +503,51 @@
     }
 
     /**
      * Called by the garbage collector on an object when garbage collection
      * determines that there are no more references to the object.
-     * A subclass overrides the <code>finalize</code> method to dispose of
+     * A subclass overrides the {@code finalize} method to dispose of
      * system resources or to perform other cleanup.
      * <p>
-     * The general contract of <tt>finalize</tt> is that it is invoked
+     * The general contract of {@code finalize} is that it is invoked
      * if and when the Java<font size="-2"><sup>TM</sup></font> virtual
      * machine has determined that there is no longer any
      * means by which this object can be accessed by any thread that has
      * not yet died, except as a result of an action taken by the
      * finalization of some other object or class which is ready to be
-     * finalized. The <tt>finalize</tt> method may take any action, including
+     * finalized. The {@code finalize} method may take any action, including
      * making this object available again to other threads; the usual purpose
-     * of <tt>finalize</tt>, however, is to perform cleanup actions before
+     * of {@code finalize}, however, is to perform cleanup actions before
      * the object is irrevocably discarded. For example, the finalize method
      * for an object that represents an input/output connection might perform
      * explicit I/O transactions to break the connection before the object is
      * permanently discarded.
      * <p>
-     * The <tt>finalize</tt> method of class <tt>Object</tt> performs no
+     * The {@code finalize} method of class {@code Object} performs no
      * special action; it simply returns normally. Subclasses of
-     * <tt>Object</tt> may override this definition.
+     * {@code Object} may override this definition.
      * <p>
      * The Java programming language does not guarantee which thread will
-     * invoke the <tt>finalize</tt> method for any given object. It is
+     * invoke the {@code finalize} method for any given object. It is
      * guaranteed, however, that the thread that invokes finalize will not
      * be holding any user-visible synchronization locks when finalize is
      * invoked. If an uncaught exception is thrown by the finalize method,
      * the exception is ignored and finalization of that object terminates.
      * <p>
-     * After the <tt>finalize</tt> method has been invoked for an object, no
+     * After the {@code finalize} method has been invoked for an object, no
      * further action is taken until the Java virtual machine has again
      * determined that there is no longer any means by which this object can
      * be accessed by any thread that has not yet died, including possible
      * actions by other objects or classes which are ready to be finalized,
      * at which point the object may be discarded.
      * <p>
-     * The <tt>finalize</tt> method is never invoked more than once by a Java
+     * The {@code finalize} method is never invoked more than once by a Java
      * virtual machine for any given object.
      * <p>
-     * Any exception thrown by the <code>finalize</code> method causes
+     * Any exception thrown by the {@code finalize} method causes
      * the finalization of this object to be halted, but is otherwise
      * ignored.
      *
-     * @throws Throwable the <code>Exception</code> raised by this method
+     * @throws Throwable the {@code Exception} raised by this method
      */
     protected void finalize() throws Throwable { }
 }