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();
2.如果两个对象通过equal方法判断是相同的话，那么他们通过hashCode方法的返回值一定是一样的
3.两个对象如果通equal方法的返回值是false，他们通过hashCode方法的返回值不一定是不同的；然而，我们应该意识到对于不相等的对象返回不同的hashCode值能够提高hash表的性能
