Why is “a^=b^=a^=b;” different from “a^=b; b^=a; a^=b;”?

Question

I tried some code to swap two integers in Java without using a 3rd variable, using XOR.

Here are the two swap functions I tried:

package lang.numeric         


        

Answer 1

Because a ^= b ^= a ^= b; is parsed like:

a ^= (b ^= (a ^= b));

Which can be reduced to:

a ^= (b ^= (a ^ b));

So b will have the value b ^ (a ^ b) and finally a will be a ^ (b ^ (a ^ b).