Reference assignment query?

[castiel]

I was wondering why this doesn't work. I thought when I said
val2 = val1 that I was saying that val2 points to the same memory address
as val1 and so my modifying the value of val2 I am also modifying the value of
val1 but I've noticed for Integer and String that the values are not equal when modified.

E.g.

Integer val1 = new Integer(10);
Integer val2 = val1;
val2++;
System.out.println(val1);

Expected Value of val1: 11
Actual Value of val1: 10

This referencing works for my own objects

Point p1 = new Point(5,10);
Point p2 = p1;
p2.x = 1000;
System.out.println(p1.x);

Expected Value of p1.x = 1000
Actual Value of p1.x = 1000

Can someone please tell me what's so special about Integer and String and why they behave differently? If there's any good explanation about this on the web I would be happy to read.

Cheers

[revathi17]

autoboxing - When comparing two Integers in Java does auto-unboxing occur? - Stack Overflow

[Tolls]

Primitive wrapper objects like Integer are immutable. That is, you cannot change the data in them after creation. String is the same.

As revathi17 has shown, what you see for Integer is a side effect of auto-boxing. The call to '++' results in a dereference of val2 to an int, then it is incremented, then that int is rewrapped into a new Integer. So val2 is no longer '==' val1.

The following:

    public static void main(String[] args) throws Exception {
            Integer val1 = 10;
            Integer val2 = val1;
            System.out.println(val1 == val2);
            val2++;
            System.out.println(val1 == val2);
    }

results in true then false.