casacaded assignment : Java Glossary

2008-04-12 by Roedy Green ©1996-2008 Canadian Mind Products
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cascaded assignment

In Java is it possible to cascade, aka chain assignment operators, but it is in generally considered poor form since the code often surprises the average programmer with its effects. Consider the following correct code to swap a and b without using an intermediate temporary:

int a=4;
int b=5;
a ^= b; // a=1, b=5
b ^= a; // a=1, b=4
a ^= b; // a=5, b=4

You might think you could collapse that program like this, as you can in some C++ compilers. It may not be legitimate C++, but some compilers allow it. However, in Java it does not work. You just get a=0.

int a=4;
int b=5;
a ^= b ^= a ^= b;

Even adding parentheses does not help:

int a=4;
int b=5;
a ^= ( b ^= ( a ^= b ) );

As a general rule, avoid cascading any of the Java combo assign/compute operators such as ^= += -= *= /= %= &= |= <<= >>= >>>= or =, especially when you use the same variable both on the left and right of an assignment operator.

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