Mutable or immutable class?

Question

I had read in some design book that immutable class improves scalability and its good practice to write immutable class wherever possible. But I think so immutable class inc

Answer 1

I think, if you want to share the same object among different variables, it needs to be immutable.

For instance:

String A = "abc";
String B = "abc";

String object in Java is immutable. Now both A & B point to the same "abc" string. Now

A = A + "123";
System.out.println(B);

it should output:

abc

Because String is immutable, A will simply point to new "abc123" string object instead of modifying the previous string object.