Another string pool clarification

Question

      public static void main(String[] args) {
          char[] diff = new char[]{'D','i','f','f','e','r'};
          String s = new String(diff);
          String t = new String(diff);
          System.out.println(System.identityHashCode(s));
          System.out.println(System.identityHashCode(s.intern()));
     }Both the sysouts print different values. Doesnt this mean there is an already existing reference in the pool? Any idea how that came?

Answer 1

Yes you are right. But this was not for application coding purposes. So clarifying the intent.
     public static void main(String[] args) {
          String a = "hi";
          String b = "How";
          String c = "r";
          String d = "u";
          String abcd = a + b + c + d;
          System.out.println(abcd);
          char[] aA = new char[]{'h','i'};
          char[] aB = new char[]{'H','o','w'};
          char[] aC = new char[]{'r'};
          char[] aD = new char[]{'u'};
          char[] aABCD = new char[]{'h','i','H','o','w','r','u'};
          System.out.println(a == new String(aA).intern());  //prints true
          System.out.println(b == new String(aB).intern());  //prints true
          System.out.println(c == new String(aC).intern());  //prints true
          System.out.println(d == new String(aD).intern());  //prints true
          System.out.println(abcd == new String(aABCD).intern());  //prints false
     }Just wanted to be sure programatically how appending works exactly. Different forums and books are not so clear about it. Well the fact that string reference 'abcd' is not in the pool was something new to me (based on the assumption that at least that part of the javadoc for intern method is correct). But because of the change in spec for the intern method there is no way to check whether string "hiHow" is in the pool because we need a reference to it. But if the string abcd is not in the pool i guess "hiHow" will also not be.
Thats the whole thing. And a conclusion, intern method will not let you help check the pool whether a string is in it, if you already dont have the reference to the literal and this is because of the change in the spec while implementation. If the javadoc were correct you could have done like below to see if the string is not in the pool.
     public static void main(String[] args) {
          char[] aAB = new char[]{'h','i','H','o','w'};
          String ab = new String(aAB);
          if(ab != ab.intern()){
               System.out.println("alerady in pool");
          }else{
               System.out.println("Only now in pool");
     }But now that the method puts a copy in the pool, we never know.