如果（假）多次执行是不是很糟糕？

Question

If I have a piece of code like so...

if(!hasRunMethod) {
    runMethod();
    hasRunMethod = true;
}

...and that code is being executed in a loop over and over, many times every second, even though the code inside is only called once, is this bad coding practice? If so, what should I do instead?

Answer 1

Quickly tested (on java version 1.8.0_05):

long start = System.nanoTime();
int run = 1_000_000;
for(int i = 0; i < run; ++i) {
    if(alwaysTrue) {

    }
}
long end = System.nanoTime();

end - start averages ~1,820,000 nano seconds. this:

long start = System.nanoTime();
int run = 1_000_000;
for(int i = 0; i < run; ++i) {
    // if(alwaysTrue) {
    //   
    // }
}
long end = System.nanoTime();

end - start averages ~1,556,000 nano seconds.

as an added bonus:

long start = System.nanoTime();
int run = 1_000_000;
for(int i = 0; i < run; ++i) {
    if(true) {

    }
}
long end = System.nanoTime();

end - start averages ~1,542,000 nano seconds, same as commented out.

Conclusion

if(someBool){} inside a loop has some performance impact. But it's so negligible I find it hard to think of a bottleneck sensitive enough for it to matter.