面试(1)-java-se-字符串

http://blog.csdn.net/zhangerqing/article/details/8093919

hashCode和identityHashCode的区别

I、 hashCode()方法是Object类下面的一个方法，供继承类重写，根据对象内存地址计算哈希值，String类重写了hashCode方法，并改为根据字符序列来计算哈希值

II、identityHashCode()方法是System类中的静态方法，根据对象内存地址来计算哈希值；

方法示例：

    public static void main(String[] args)
    {
        // 下面程序中s1和s2是两个不同对象
        String s1 = new String("Hello");
        String s2 = new String("Hello");
        // String类重写了Object类的hashCode方法——改为根据字符序列计算hashCode值，
        // 因为s1和s2的字符序列相同，所以它们的hashCode方法返回值相同
        System.out.println(s1.hashCode() + "----" + s2.hashCode());
        // s1和s2是不同的字符串对象，所以它们的identityHashCode值不同，
        // identityHashCode是根据对象的地址计算得到的，所以任何两个不同的对象的
        // identityHashCode值总是不相等
        System.out.println(System.identityHashCode(s1) + "----"+ System.identityHashCode(s2));
        // s3和s4是相同的字符串对象，所以它们的identityHashCode值相同
        String s3 = "Java";
        String s4 = "Java";
        System.out.println(System.identityHashCode(s3) + "----"+ System.identityHashCode(s4));
    }

输出：

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