JavaSE_坚持读源码_Object对象_Java1.7

最新推荐文章于 2025-08-17 21:38:20 发布

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原文链接：http://www.cnblogs.com/rocker-pg/p/8994100.html

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本文详细解释了hashCode方法的通用契约及其与equals方法的关系。hashCode应该为相等的对象提供相同的整数值，并尽可能为不相等的对象提供不同的整数，以优化哈希表性能。

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 1  /**
 2      * Returns a hash code value for the object. This method is
 3      * supported for the benefit of hash tables such as those provided by
 4      * {@link java.util.HashMap}.
 5      * <p>
 6      * The general contract of {@code hashCode} is:
 7      * <ul>
 8      * 1.<li>Whenever it is invoked on the same object more than once during
 9      *     an execution of a Java application, the {@code hashCode} method
10      *     must consistently return the same integer, provided no information
11      *     used in {@code equals} comparisons on the object is modified.
12      *     This integer need not remain consistent from one execution of an
13      *     application to another execution of the same application.
14      * 2. <li>If two objects are equal according to the {@code equals(Object)}
15      *     method, then calling the {@code hashCode} method on each of
16      *     the two objects must produce the same integer result.
17      * 3.<li>It is <em>not</em> required that if two objects are unequal
18      *     according to the {@link java.lang.Object#equals(java.lang.Object)}
19      *     method, then calling the {@code hashCode} method on each of the
20      *     two objects must produce distinct integer results.  However, the
21      *     programmer should be aware that producing distinct integer results
22      *     for unequal objects may improve the performance of hash tables.
23      * </ul>
24      * <p>
25      * As much as is reasonably practical, the hashCode method defined by
26      * class {@code Object} does return distinct integers for distinct
27      * objects. (This is typically implemented by converting the internal
28      * address of the object into an integer, but this implementation
29      * technique is not required by the
30      * Java<font size="-2"><sup>TM</sup></font> programming language.)
31      *
32      * @return  a hash code value for this object.
33      * @see     java.lang.Object#equals(java.lang.Object)
34      * @see     java.lang.System#identityHashCode
35      */
36     public native int hashCode();