Nigel I dont know 1.5 but I know 1.4
See Strings objects are immutable, reference variable are not.
String s=new String("Hello");
String s1=new String("World");
s=s1; // now s points to String "World"
// Hello did not change
so objects are immutable means their value cant be changed but
reference pointing to them can change as reference are not immutable.
same with wrapper,
hope this helps correct me if so think so.