is checking a boolean faster than setting a boolean in java?

Question

This:

if (var) {
    var = false;
}

Versus this:

var = false;

Is there a speed difference?

Answer 1

Here's another cheap "benchmark" (which almost doesn't deserve the term). To me, the results of Monkey Wrench's benchmark were not clearly speaking in regards to OP's question, so I thought I should put it here, too.

Result (under these conditions, and quite few tests only): Checking a local boolean before writing it is better than writing it often if not necessary.

public static void main(String[] args) {

    final Random r = new Random(0);

    boolean b = false;
    boolean decision;

    long startTime;
    long endTime;

    startTime = System.currentTimeMillis();
    for (long i = 0; i < 1000000000; i++) {
        decision = r.nextDouble() > 0.1; // Will be true MOST of the time.

        if (decision) {

            // if (!b) {
                b = true;
            // }

        }
    }
    endTime = System.currentTimeMillis();

    System.err.println(endTime - startTime);
    System.err.println(b);

    System.exit(0);
}

With bluntly writing (ms):
18139
18140
18196
(18220)
(18181)
----------
Average of 3: 18158.333333333333333333333333333
Average of 5: 18175.2


With checking before writing (ms):
18097
18109
18115
(18129)
(18133)
----------
Average of 3: 18107
Average of 5: 18116.6


With checking, it only takes this % (3 samples): 99.71730151445617255621844882974
With checking, it only takes this % (5 samples): 99.677582640080989480170782164708

With checking, it takes about 99.7 % of the blunt-writing time. If the write would otherwise happen unnecessarily very often. In this crappy "benchmark", that is.