class Swap1 { public static void main(String args[]) { int a = 1; int b = 2; System.out.println("a +a); System.out.println("b +b); // swap a and b a = b; b = a; System.out.println("a +a); System.out.println("b +b); } } This produces the following output:

a = 1 b = 2 a = 2 b = 2 That isn't what you expected! The problem is that we lost track of the value 1 when we put the value of b into a . To correct this we need to introduce a third variable, temp , to hold the original value of a .

class Swap2 { public static void main(String args[]) { int a = 1; int b = 2; int temp; System.out.println("a +a); System.out.println("b +b); // swap a and b temp = a; a = b; b = temp; System.out.println("a +a); System.out.println("b +b); } } This code produces the output we expect:

a = 1 b = 2 a = 2 b = 1