swap : Java Glossary


// swap int variables a and b
int a = 1;
int b = 2;
// save a copy of "a" you are about to clobber
int swap = a;
a = b;
b = swap;
// swap references a and b
Thing a = new Thing( 1 );
Thing b = new Thing( 2 );
// save a copy of "a" you are about to clobber
Thing swap = a;
a = b;
b = swap;
// avoid packratting Thing( 1 )
swap = null;
It is possible to swap two values without using a temporary using XOR (exclusive OR). Don’t use this technique without a serious
// Swap references a and b without a temporary
// It works on the principle that if you xor
// with something twice you
// get back to where you started.
// Note, this is slower than using a swap temp variable.
int a = 17;
int b = 42;
a = a ^ b;
b = a ^ b; // a ^ b ^ b = a
a = a ^ b; // a ^ b ^ a ^ b ^ b = b
If you try to encapsulate this logic in a method, it will have no effect on the caller’s variables. You have to expand it Further, the XOR technique cannot be used on two Objects in Java, the only time there would be a pressing advantage to it. I present it more as a curiosity from a bygone age.

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