What is the fastest looping in Java?

Question

Recently, I want to optimize my code. Would any one tell how to speed up looping? While-loop is faster than for-loop? And which type of for-loop is faster?

It is surely I am not talking about a empty content looping. I mean If any good way to loop a huge data in Java or Python.

And I got the answer from here

Answer 1

“We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%.A good programmer will not be lulled into complacency by such reasoning, he will be wise to look carefully at the critical code; but only after that code has been identified”

faster at what looping? what is in the loop is what takes the time, a loop that does nothing is the fastest ... this question makes no sense.

the lesson here is that the actual instructions for the looping construct are sub-microseconds and highly optimized already in all the languages you mention ( Java, Python and C ( with a modern compiler ) ).

what is going on in your loop is going to have way more impact than the few instructions that any of the looping constructs will have. If your code is 100,000 instructions, do you really care if one loop construct takes 3 instructions and another takes 2?

Answer 2

The actual loop is not what's going to speed up your code.

You should find better algorithms for what you're doing IN the loop, and go from there.

Also, don't forget that you should only optimize your code if it's too slow for your purposes!

There's a little more here, if you're interested.

Answer 3

While- and for-loops are the same thing at runtime. I'm not sure what you mean by "type" of for-loop.

Your questions pre-supposes that the looping construct itself takes up significant time. That is extremely unlikely - it's the body of the loop that would take time. You should profile your code to see exactly where the bottlenecks are and then optimise those.

Answer 4

The fastest loop is the one that does nothing.

To optimize your application you first have to:

• have it working properly.

Then

• use a profiler to identify bottlenecks

And finally

• improve the detected spots. Most of the times using a new algorithm will do.

As for which is faster for or while loops, they are equivalent so don't look there.

If you have an specific problem we could help you. For a Java sample on how to use Java VisualVM you can see this other question:Trying to solve 15 Puzzle, OutOfMemoryError

Answer 5

In any of these languages:

for(int i = 0; i < n; ++i) {
   doSomethingWith(i);
}

is equivalent to:

int i = 0;
while(i < n) {
   doSomethingWith(i);
   ++i;
}

That said, there are techniques for optimizing loops, for example loop unrolling:

for(int i = 0; i < n; i += 4) {
   doSomethingWith(i);
   doSomethingWith(i+1);
   doSomethingWith(i+2);
   doSomethingWith(i+3);
}

However, in almost all cases it is best to let the compiler do it for you automatically.

Bottom line: I concur with the general opinions expressed here. First make sure that what is in the loop is the bottleneck. If it is, try to optimize what is in the loop.

Answer 6

while(1) {} / for (;;); / do {} while(1); is clearly the fastest, on x86 it will assemble to:

label:
jmp label

0/0 (100%) work per clock cycle, pretty good if you ask me