Java: Why does this swap method not work?

I have the following code:

public class Main {

    static void swap (Integer x, Integer y) {
        Integer t = x;
        x = y;
        y = t;
    }

    public static void main(String[] args) {

       Integer a = 1;
       Integer b = 2;
       swap(a, b);
       System.out.println("a=" + a + " b=" + b);
    } 
}

I expect it to print a=2 b=1, but it prints the opposite. So obviously the swap method doesn't swap a and b values. Why?

Answer

This doesn't have anything to do with immutability of integers; it has to do with the fact that Java is Pass-by-Value, Dammit! (Not annoyed, just the title of the article :p )

To sum up: You can't really make a swap method in Java. You just have to do the swap yourself, wherever you need it; which is just three lines of code anyways, so shouldn't be that much of a problem :)

    Thing tmp = a;
    a = b;
    b = tmp;