public static void test(StringBuffer a, StringBuffer b) {
        System.out.println("1--->" + a);// 1
        System.out.println("2--->" + b);// 2
        b = a;// 3
        a = new StringBuffer("new");// 4
        System.out.println("5--->" + a);// 5
        System.out.println("6--->" + b);// 6
        a.append("hah");// 7
        b.append("hah");// 8
        System.out.println("7--->" + a);// 9
        System.out.println("8--->" + b);// 10
    }

    public static void main(String[] args) {
        StringBuffer s = new StringBuffer("good");// d1
        StringBuffer s2 = new StringBuffer("bad");// d2
        test(s, s2); // d3
        System.out.println(s);// d4
        System.out.println(s2);// d5
    }