Java: Why does this swap method not work? [duplicate]

Question

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 1

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; 

Answer 2

Everything in Java is passed by value and the values of variables are always primitives or references to object.