public void test(){
    
    String s1 = "ab" + "c";
    String s2 = "abc";
    System.out.println(s1 == s2 + ":" +s1.equals(s2));
  }

public static void main(String[] args) {
        String a = new String("abcd");
        String b = new String("abcd");
        String c = "abcd" + "ppp";
        String d = "abcd";
        String e = "abcd" + "ppp";
        String f = d + "ppp";

        System.out.println((a == b) + "-------------" + a.equals(b));
        System.out.println((a == d) + "-------------" + a.equals(d));
        System.out.println((b == d) + "-------------" + b.equals(d));
        System.out.println((c == e) + "-------------" + c.equals(e));
        System.out.println((f == e) + "-------------" + f.equals(e));
        a = a.intern();
        System.out.println((a == d) + "-------------" + a.equals(d));
    }

false-------------true
false-------------true
false-------------true
true-------------true
false-------------true
true-------------true