Java HasCode equals == 的区别

==

用来判断两个值，或者两个对象的内存地址是否一样。

equals

equals 方法用来判断两个对象是否相等。equals 是Object 类的方法，默认情况下，比较两个对象是否是同一个对象，内部通过 == 实现。如果想比较两个对象的其他内容，则可以通过重写equals 方法。比如String 就重写了equals 方法。

equals是Object类的方法，默认情况下比较两个对象是否是同一个对象，内部实现是通过“==”来实现的。

如果想比较两个对象的其他内容，则可以通过重写equals方法，

例如：String类就重写了equals方法，改成了对象的内容是否相等。

hasCode方法：

    /**
     * Returns a hash code value for the object. This method is
     * supported for the benefit of hash tables such as those provided by
     * {@link java.util.HashMap}.
     * <p>
     * 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 {@code hashCode} method
     *     must consistently return the same integer, provided no information
     *     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 {@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 {@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 hash tables.
     * </ul>
     * <p>
     * As much as is reasonably practical, the hashCode method defined by
     * 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&trade; programming language.)
     *
     * @return  a hash code value for this object.
     * @see     java.lang.Object#equals(java.lang.Object)
     * @see     java.lang.System#identityHashCode
     */
    public int hashCode() {
        return identityHashCode(this);
    }

hasCode 这个方法会在HasMap 里面使用到。
通常来说，在一次程序运行期间，一个对象的hasCode 是不变的。在不同的程序运行期间可以不同。
如果两个对象的equals的方法返回的值是相等的，那么hasCode 就应该返回一样的值。

不同的对象的hasCode可能是一样的。但是不同对象返回不同hasCode 能够提高has 表的性能。

同一个类，new 出来两个实例，他们俩的hasCode 是不一样的。