/**

     * String之所以被称为不可变字符串

     */

    static void testString(){

        String str = "i love";

        System.out.println(str+"地址是："+System.identityHashCode(str));

        str = str+" you";

        System.out.println(str+"地址是："+System.identityHashCode(str));

        StringBuffer sb =new StringBuffer("i love");

        System.out.println(sb+"地址是："+System.identityHashCode(sb));

        sb.append(" you");

        System.out.println(sb+"地址是："+System.identityHashCode(sb));

    }