Which is more effective: if (null == variable) or if (variable == null)? [duplicate]

Answer 1

My opinion: Don't care about such insignificant performance optimizations. If you have bad performance, find and target the real problems/bottlenecks in your code.

Answer 2

No difference.

if (variable == null) is (imo) a better programming style.

Note that null is lowercase in Java.

Answer 3

There is no material difference from a performance perspective.

However... what if you made a typo and missed a single equals character?

foo = null; // assigns foo to null at runtime... BAD!

versus

null = foo; // compile time error, typo immediately caught in editor,
developer gets 8 hours of sleep

This is one argument in favor of beginning an if test with null on the left hand side.

The second argument in favor of beginning an if test with null is that it's made very clear to the reader of the code that they are looking at a null test, even when the expression on the right of the equals sign is verbose.

@aiooba points this second argument out as well:

For certain situations however, I tend to put the null in front. For instance in the following case:

String line;
while (null != (line = reader.readLine()))
    process(line);