6239194: Object.hashCode() should reference System.identityHashCode()
Reviewed-by: emcmanus
This commit is contained in:
Joe Darcy
parent
40754a9924
commit
3f450f06e2
@ -26,8 +26,8 @@
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package java.lang;
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/**
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* Class <code>Object</code> is the root of the class hierarchy.
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* Every class has <code>Object</code> as a superclass. All objects,
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* Class {@code Object} is the root of the class hierarchy.
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* Every class has {@code Object} as a superclass. All objects,
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* including arrays, implement the methods of this class.
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*
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* @author unascribed
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@ -66,30 +66,30 @@ public class Object {
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/**
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* Returns a hash code value for the object. This method is
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* supported for the benefit of hashtables such as those provided by
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* <code>java.util.Hashtable</code>.
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* supported for the benefit of hash tables such as those provided by
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* {@link java.util.HashMap}.
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* <p>
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* The general contract of <code>hashCode</code> is:
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* The general contract of {@code hashCode} is:
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* <ul>
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* <li>Whenever it is invoked on the same object more than once during
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* an execution of a Java application, the <tt>hashCode</tt> method
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* an execution of a Java application, the {@code hashCode} method
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* must consistently return the same integer, provided no information
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* used in <tt>equals</tt> comparisons on the object is modified.
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* used in {@code equals} comparisons on the object is modified.
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* This integer need not remain consistent from one execution of an
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* application to another execution of the same application.
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* <li>If two objects are equal according to the <tt>equals(Object)</tt>
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* method, then calling the <code>hashCode</code> method on each of
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* <li>If two objects are equal according to the {@code equals(Object)}
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* method, then calling the {@code hashCode} method on each of
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* the two objects must produce the same integer result.
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* <li>It is <em>not</em> required that if two objects are unequal
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* according to the {@link java.lang.Object#equals(java.lang.Object)}
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* method, then calling the <tt>hashCode</tt> method on each of the
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* method, then calling the {@code hashCode} method on each of the
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* two objects must produce distinct integer results. However, the
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* programmer should be aware that producing distinct integer results
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* for unequal objects may improve the performance of hashtables.
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* for unequal objects may improve the performance of hash tables.
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* </ul>
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* <p>
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* As much as is reasonably practical, the hashCode method defined by
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* class <tt>Object</tt> does return distinct integers for distinct
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* class {@code Object} does return distinct integers for distinct
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* objects. (This is typically implemented by converting the internal
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* address of the object into an integer, but this implementation
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* technique is not required by the
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@ -97,55 +97,55 @@ public class Object {
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*
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* @return a hash code value for this object.
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* @see java.lang.Object#equals(java.lang.Object)
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* @see java.util.Hashtable
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* @see java.lang.System#identityHashCode
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*/
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public native int hashCode();
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/**
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* Indicates whether some other object is "equal to" this one.
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* <p>
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* The <code>equals</code> method implements an equivalence relation
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* The {@code equals} method implements an equivalence relation
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* on non-null object references:
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* <ul>
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* <li>It is <i>reflexive</i>: for any non-null reference value
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* <code>x</code>, <code>x.equals(x)</code> should return
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* <code>true</code>.
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* {@code x}, {@code x.equals(x)} should return
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* {@code true}.
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* <li>It is <i>symmetric</i>: for any non-null reference values
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* <code>x</code> and <code>y</code>, <code>x.equals(y)</code>
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* should return <code>true</code> if and only if
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* <code>y.equals(x)</code> returns <code>true</code>.
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* {@code x} and {@code y}, {@code x.equals(y)}
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* should return {@code true} if and only if
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* {@code y.equals(x)} returns {@code true}.
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* <li>It is <i>transitive</i>: for any non-null reference values
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* <code>x</code>, <code>y</code>, and <code>z</code>, if
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* <code>x.equals(y)</code> returns <code>true</code> and
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* <code>y.equals(z)</code> returns <code>true</code>, then
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* <code>x.equals(z)</code> should return <code>true</code>.
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* {@code x}, {@code y}, and {@code z}, if
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* {@code x.equals(y)} returns {@code true} and
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* {@code y.equals(z)} returns {@code true}, then
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* {@code x.equals(z)} should return {@code true}.
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* <li>It is <i>consistent</i>: for any non-null reference values
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* <code>x</code> and <code>y</code>, multiple invocations of
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* <tt>x.equals(y)</tt> consistently return <code>true</code>
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* or consistently return <code>false</code>, provided no
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* information used in <code>equals</code> comparisons on the
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* {@code x} and {@code y}, multiple invocations of
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* {@code x.equals(y)} consistently return {@code true}
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* or consistently return {@code false}, provided no
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* information used in {@code equals} comparisons on the
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* objects is modified.
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* <li>For any non-null reference value <code>x</code>,
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* <code>x.equals(null)</code> should return <code>false</code>.
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* <li>For any non-null reference value {@code x},
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* {@code x.equals(null)} should return {@code false}.
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* </ul>
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* <p>
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* The <tt>equals</tt> method for class <code>Object</code> implements
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* The {@code equals} method for class {@code Object} implements
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* the most discriminating possible equivalence relation on objects;
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* that is, for any non-null reference values <code>x</code> and
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* <code>y</code>, this method returns <code>true</code> if and only
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* if <code>x</code> and <code>y</code> refer to the same object
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* (<code>x == y</code> has the value <code>true</code>).
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* that is, for any non-null reference values {@code x} and
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* {@code y}, this method returns {@code true} if and only
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* if {@code x} and {@code y} refer to the same object
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* ({@code x == y} has the value {@code true}).
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* <p>
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* Note that it is generally necessary to override the <tt>hashCode</tt>
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* Note that it is generally necessary to override the {@code hashCode}
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* method whenever this method is overridden, so as to maintain the
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* general contract for the <tt>hashCode</tt> method, which states
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* general contract for the {@code hashCode} method, which states
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* that equal objects must have equal hash codes.
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*
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* @param obj the reference object with which to compare.
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* @return <code>true</code> if this object is the same as the obj
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* argument; <code>false</code> otherwise.
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* @return {@code true} if this object is the same as the obj
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* argument; {@code false} otherwise.
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* @see #hashCode()
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* @see java.util.Hashtable
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* @see java.util.HashMap
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*/
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public boolean equals(Object obj) {
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return (this == obj);
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@ -154,7 +154,7 @@ public class Object {
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/**
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* Creates and returns a copy of this object. The precise meaning
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* of "copy" may depend on the class of the object. The general
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* intent is that, for any object <tt>x</tt>, the expression:
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* intent is that, for any object {@code x}, the expression:
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* <blockquote>
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* <pre>
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* x.clone() != x</pre></blockquote>
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@ -162,49 +162,49 @@ public class Object {
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* <blockquote>
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* <pre>
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* x.clone().getClass() == x.getClass()</pre></blockquote>
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* will be <tt>true</tt>, but these are not absolute requirements.
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* will be {@code true}, but these are not absolute requirements.
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* While it is typically the case that:
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* <blockquote>
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* <pre>
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* x.clone().equals(x)</pre></blockquote>
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* will be <tt>true</tt>, this is not an absolute requirement.
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* will be {@code true}, this is not an absolute requirement.
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* <p>
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* By convention, the returned object should be obtained by calling
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* <tt>super.clone</tt>. If a class and all of its superclasses (except
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* <tt>Object</tt>) obey this convention, it will be the case that
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* <tt>x.clone().getClass() == x.getClass()</tt>.
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* {@code super.clone}. If a class and all of its superclasses (except
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* {@code Object}) obey this convention, it will be the case that
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* {@code x.clone().getClass() == x.getClass()}.
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* <p>
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* By convention, the object returned by this method should be independent
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* of this object (which is being cloned). To achieve this independence,
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* it may be necessary to modify one or more fields of the object returned
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* by <tt>super.clone</tt> before returning it. Typically, this means
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* by {@code super.clone} before returning it. Typically, this means
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* copying any mutable objects that comprise the internal "deep structure"
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* of the object being cloned and replacing the references to these
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* objects with references to the copies. If a class contains only
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* primitive fields or references to immutable objects, then it is usually
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* the case that no fields in the object returned by <tt>super.clone</tt>
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* the case that no fields in the object returned by {@code super.clone}
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* need to be modified.
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* <p>
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* The method <tt>clone</tt> for class <tt>Object</tt> performs a
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* The method {@code clone} for class {@code Object} performs a
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* specific cloning operation. First, if the class of this object does
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* not implement the interface <tt>Cloneable</tt>, then a
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* <tt>CloneNotSupportedException</tt> is thrown. Note that all arrays
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* are considered to implement the interface <tt>Cloneable</tt>.
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* not implement the interface {@code Cloneable}, then a
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* {@code CloneNotSupportedException} is thrown. Note that all arrays
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* are considered to implement the interface {@code Cloneable}.
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* Otherwise, this method creates a new instance of the class of this
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* object and initializes all its fields with exactly the contents of
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* the corresponding fields of this object, as if by assignment; the
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* contents of the fields are not themselves cloned. Thus, this method
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* performs a "shallow copy" of this object, not a "deep copy" operation.
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* <p>
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* The class <tt>Object</tt> does not itself implement the interface
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* <tt>Cloneable</tt>, so calling the <tt>clone</tt> method on an object
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* whose class is <tt>Object</tt> will result in throwing an
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* The class {@code Object} does not itself implement the interface
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* {@code Cloneable}, so calling the {@code clone} method on an object
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* whose class is {@code Object} will result in throwing an
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* exception at run time.
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*
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* @return a clone of this instance.
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* @exception CloneNotSupportedException if the object's class does not
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* support the <code>Cloneable</code> interface. Subclasses
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* that override the <code>clone</code> method can also
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* support the {@code Cloneable} interface. Subclasses
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* that override the {@code clone} method can also
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* throw this exception to indicate that an instance cannot
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* be cloned.
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* @see java.lang.Cloneable
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@ -213,15 +213,15 @@ public class Object {
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/**
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* Returns a string representation of the object. In general, the
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* <code>toString</code> method returns a string that
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* {@code toString} method returns a string that
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* "textually represents" this object. The result should
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* be a concise but informative representation that is easy for a
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* person to read.
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* It is recommended that all subclasses override this method.
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* <p>
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* The <code>toString</code> method for class <code>Object</code>
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* The {@code toString} method for class {@code Object}
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* returns a string consisting of the name of the class of which the
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* object is an instance, the at-sign character `<code>@</code>', and
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* object is an instance, the at-sign character `{@code @}', and
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* the unsigned hexadecimal representation of the hash code of the
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* object. In other words, this method returns a string equal to the
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* value of:
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@ -241,7 +241,7 @@ public class Object {
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* monitor. If any threads are waiting on this object, one of them
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* is chosen to be awakened. The choice is arbitrary and occurs at
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* the discretion of the implementation. A thread waits on an object's
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* monitor by calling one of the <code>wait</code> methods.
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* monitor by calling one of the {@code wait} methods.
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* <p>
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* The awakened thread will not be able to proceed until the current
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* thread relinquishes the lock on this object. The awakened thread will
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@ -255,9 +255,9 @@ public class Object {
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* object's monitor in one of three ways:
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* <ul>
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* <li>By executing a synchronized instance method of that object.
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* <li>By executing the body of a <code>synchronized</code> statement
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* <li>By executing the body of a {@code synchronized} statement
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* that synchronizes on the object.
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* <li>For objects of type <code>Class,</code> by executing a
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* <li>For objects of type {@code Class,} by executing a
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* synchronized static method of that class.
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* </ul>
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* <p>
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@ -273,7 +273,7 @@ public class Object {
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/**
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* Wakes up all threads that are waiting on this object's monitor. A
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* thread waits on an object's monitor by calling one of the
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* <code>wait</code> methods.
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* {@code wait} methods.
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* <p>
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* The awakened threads will not be able to proceed until the current
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* thread relinquishes the lock on this object. The awakened threads
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@ -283,7 +283,7 @@ public class Object {
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* being the next thread to lock this object.
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* <p>
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* This method should only be called by a thread that is the owner
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* of this object's monitor. See the <code>notify</code> method for a
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* of this object's monitor. See the {@code notify} method for a
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* description of the ways in which a thread can become the owner of
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* a monitor.
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*
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@ -308,15 +308,15 @@ public class Object {
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* becomes disabled for thread scheduling purposes and lies dormant
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* until one of four things happens:
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* <ul>
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* <li>Some other thread invokes the <tt>notify</tt> method for this
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* <li>Some other thread invokes the {@code notify} method for this
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* object and thread <var>T</var> happens to be arbitrarily chosen as
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* the thread to be awakened.
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* <li>Some other thread invokes the <tt>notifyAll</tt> method for this
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* <li>Some other thread invokes the {@code notifyAll} method for this
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* object.
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* <li>Some other thread {@linkplain Thread#interrupt() interrupts}
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* thread <var>T</var>.
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* <li>The specified amount of real time has elapsed, more or less. If
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* <tt>timeout</tt> is zero, however, then real time is not taken into
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* {@code timeout} is zero, however, then real time is not taken into
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* consideration and the thread simply waits until notified.
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* </ul>
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* The thread <var>T</var> is then removed from the wait set for this
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@ -324,11 +324,11 @@ public class Object {
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* usual manner with other threads for the right to synchronize on the
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* object; once it has gained control of the object, all its
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* synchronization claims on the object are restored to the status quo
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* ante - that is, to the situation as of the time that the <tt>wait</tt>
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* ante - that is, to the situation as of the time that the {@code wait}
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* method was invoked. Thread <var>T</var> then returns from the
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* invocation of the <tt>wait</tt> method. Thus, on return from the
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* <tt>wait</tt> method, the synchronization state of the object and of
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* thread <tt>T</tt> is exactly as it was when the <tt>wait</tt> method
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* invocation of the {@code wait} method. Thus, on return from the
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* {@code wait} method, the synchronization state of the object and of
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* thread {@code T} is exactly as it was when the {@code wait} method
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* was invoked.
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* <p>
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* A thread can also wake up without being notified, interrupted, or
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@ -351,18 +351,18 @@ public class Object {
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*
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* <p>If the current thread is {@linkplain java.lang.Thread#interrupt()
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* interrupted} by any thread before or while it is waiting, then an
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* <tt>InterruptedException</tt> is thrown. This exception is not
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* {@code InterruptedException} is thrown. This exception is not
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* thrown until the lock status of this object has been restored as
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* described above.
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*
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* <p>
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* Note that the <tt>wait</tt> method, as it places the current thread
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* Note that the {@code wait} method, as it places the current thread
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* into the wait set for this object, unlocks only this object; any
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* other objects on which the current thread may be synchronized remain
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* locked while the thread waits.
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* <p>
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* This method should only be called by a thread that is the owner
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* of this object's monitor. See the <code>notify</code> method for a
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* of this object's monitor. See the {@code notify} method for a
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* description of the ways in which a thread can become the owner of
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* a monitor.
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*
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@ -388,7 +388,7 @@ public class Object {
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* some other thread interrupts the current thread, or a certain
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* amount of real time has elapsed.
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* <p>
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* This method is similar to the <code>wait</code> method of one
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* This method is similar to the {@code wait} method of one
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* argument, but it allows finer control over the amount of time to
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* wait for a notification before giving up. The amount of real time,
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* measured in nanoseconds, is given by:
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@ -398,17 +398,17 @@ public class Object {
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* <p>
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* In all other respects, this method does the same thing as the
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* method {@link #wait(long)} of one argument. In particular,
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* <tt>wait(0, 0)</tt> means the same thing as <tt>wait(0)</tt>.
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* {@code wait(0, 0)} means the same thing as {@code wait(0)}.
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* <p>
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* The current thread must own this object's monitor. The thread
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* releases ownership of this monitor and waits until either of the
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* following two conditions has occurred:
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* <ul>
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* <li>Another thread notifies threads waiting on this object's monitor
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* to wake up either through a call to the <code>notify</code> method
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* or the <code>notifyAll</code> method.
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* <li>The timeout period, specified by <code>timeout</code>
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* milliseconds plus <code>nanos</code> nanoseconds arguments, has
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* to wake up either through a call to the {@code notify} method
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* or the {@code notifyAll} method.
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* <li>The timeout period, specified by {@code timeout}
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* milliseconds plus {@code nanos} nanoseconds arguments, has
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* elapsed.
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* </ul>
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* <p>
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@ -425,7 +425,7 @@ public class Object {
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* }
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* </pre>
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* This method should only be called by a thread that is the owner
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* of this object's monitor. See the <code>notify</code> method for a
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* of this object's monitor. See the {@code notify} method for a
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* description of the ways in which a thread can become the owner of
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* a monitor.
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*
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@ -465,13 +465,13 @@ public class Object {
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* {@link java.lang.Object#notify()} method or the
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* {@link java.lang.Object#notifyAll()} method for this object.
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* In other words, this method behaves exactly as if it simply
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* performs the call <tt>wait(0)</tt>.
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* performs the call {@code wait(0)}.
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* <p>
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* The current thread must own this object's monitor. The thread
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* releases ownership of this monitor and waits until another thread
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* notifies threads waiting on this object's monitor to wake up
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* either through a call to the <code>notify</code> method or the
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* <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
|
||||
@ -484,7 +484,7 @@ public class Object {
|
||||
* }
|
||||
* </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.
|
||||
*
|
||||
@ -505,49 +505,49 @@ public class Object {
|
||||
/**
|
||||
* 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 { }
|
||||
}
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user