Puzzle (Swap Meat)

Consider the following example.

package demo;

public class App {
  public static void main( String[] args ) {
    cleverSwap();
  }

  public static void cleverSwap() {
    int x = 1984;  // (0x7c0)
    int y = 2001;  // (0x7d1)
    x ^= y ^= x ^= y;
    System.out.printf( "x = %d; y = %d%n", x, y );
  }
}

Unfortunately the above swap variables trick does not work in Java.

x = 0; y = 1984

This example was taken from PUZZLE 7: SWAP MEAT in Java™ Puzzlers: Traps, Pitfalls, and Corner Cases.

“Long ago, when central processing units had few registers, it was discovered that one could avoid the use of a temporary variable by taking advantage of the property of the exclusive OR operator (^) that (x ^ y ^ x) == y”

“This idiom was used in the C programming language and from there made its way into C++ but is not guaranteed to work in either of these languages. It is guaranteed not to work in Java. The Java language specification says that operands of operators are evaluated from left to right (JLS 15.7). To evaluate the expression x ^= expr, the value of x is sampled before expr is evaluated, and the exclusive OR of these two values is assigned to the variable x (JLS 15.26.2). In the cleverSwap() function, the variable x is sampled twice—once for each appearance in the expression—but both samplings occur before any assignments.”