Query on Strings in point of memory..?

Question

Can any one explain the below code clearly in point of memory?
String A = new String("abc"); // 1. How many objects are created here?
String B = "def"; //2. How many objects here?
A = A + B; // Here Value of A is 'abcdef'.
As we know String objects are immutable. The value of A is visible here 'abcdef' why cannt only 'abc'. Here reference of A was changed but how can we prove here the value of A is same at any time..? Plz explain clearly.

Answer 1

String A = new String("abc"); // 1. How manyobjects
are created here?One.
I heard that in above statement two objects are
created. this is one in String Constant Pool and
anothe is in Heap memory. Is it right?
If not wht is the use of String Constant Pool? If it
is right why String Objects are create in Heap as
well as String Constant Pool?I think it's correct that "abc" is placed in contant pool, and that new String creates yet another object.
You can verify that a string is immutable by executing the following code.
String a = "abc";
String tmp = a;
String a = a.concat("def");
System.out.println(a);
System.out.println(tmp);Kaj