String面试题

String.intern()方法返回常量池中和String对象的值相同的常量的引用,如果常量池中没有该常量,则把该String对象的值加入常量池

        String s1 = "programming";
        String s2 = new String("programming");
        String s3 = "program";
        String s4 = "ming";
        String s5 = "program" + "ming";
        String s6 = s3 + s4; // s6指向新的对象
        System.out.println(s1 == s2); // false
        System.out.println(s1 == s5); // true
        System.out.println(s1 == s6); // false
        System.out.println(s1 == s6.intern()); // true
        System.out.println(s2 == s2.intern()); // false
        System.out.println(s1 == s2.intern()); // true
        System.out.println(s6 == s6.intern()); // false