Hello Community,

you probably often thought about what is the fastest/most efficient way of looping...

So according to the DalvikVM designer Dan Bornstein these are the fastest ways of looping, sorted from fast to slow. (If you do it like 1, 2 or 3 you should not worry)


This is where I extracted that information from (jump to minute ~40):
[align=center][youtube]http://www.youtube.com/watch?v=ptjedOZEXPM[/youtube][/align]

Regards,
plusminus

Extra check against 0, or no check at all, hmm... Of course exception handling isn't cheap, but if you're worried about optimizing a loop, it's likely being executed pretty darn often anyway.

If the loop is 100000 items long, your exception handling solution is pretty cool, but otherwise (with small arrays) it's not very fast I guess.

Note on Arraylists: For Arraylists (actually Itetable) it's not adviced to use the enhanced for loop (for (T item:array)) you'd better do:

According to the docs, this is faster.

MrSnowflake wrote:If the loop is 100000 items long, your exception handling solution is pretty cool, but otherwise (with small arrays) it's not very fast I guess.

Note on Arraylists: For Arraylists (actually Itetable) it's not adviced to use the enhanced for loop (for (T item:array)) you'd better do:

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

Using java Syntax Highlighting

1. int size = arraylist.count(); //or size I don't know out of my head.
2. for (int i = 0; i < size; ++i)
3.   arraylist.get(i);

Parsed in 0.036 seconds, using GeSHi 1.0.8.4

According to the docs, this is faster.

If you keep reallocating them in an inner loop, that is going to affect performance, otherwise I think you will find the iterators to be preferable.

In my app Bookamak, I took a for-each loop with 'Element' classes (it contains every information about 'one' sheet on the pinboard). From there I extracted 6 String values per sheet necessary for rendering.

When there are >30 coloured sheet on the visible screen, scrolling screen gets a bit slower, so I tried to replace the for-each(Element) with a simple for-loop and String[] , in the hope of gaining performance.

The result was: scrolling became even slower especially with a small number of sheet, for-each works much better for me... so I returned to it.

spokebloke wrote:

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

Using java Syntax Highlighting

1. try {
2.     for(int i = 0; ; ++i) {
3.     }
4. } catch (ArrayIndexOutOfBoundsException e)
5.     // Finished loop, do nothing
6. }

Parsed in 0.038 seconds, using GeSHi 1.0.8.4

Extra check against 0, or no check at all, hmm... Of course exception handling isn't cheap, but if you're worried about optimizing a loop, it's likely being executed pretty darn often anyway.

Congratulations, that has to be the worst use of exceptions ever. Absolutely horrible.

rejser wrote:

spokebloke wrote:

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

Using java Syntax Highlighting

1. try {
2.     for(int i = 0; ; ++i) {
3.     }
4. } catch (ArrayIndexOutOfBoundsException e)
5.     // Finished loop, do nothing
6. }

Parsed in 0.036 seconds, using GeSHi 1.0.8.4

Extra check against 0, or no check at all, hmm... Of course exception handling isn't cheap, but if you're worried about optimizing a loop, it's likely being executed pretty darn often anyway.

Congratulations, that has to be the worst use of exceptions ever. Absolutely horrible.

True, but for huge arrays, he does have a point .

rejser wrote:

spokebloke wrote:

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

Using java Syntax Highlighting

1. try {
2.     for(int i = 0; ; ++i) {
3.     }
4. } catch (ArrayIndexOutOfBoundsException e)
5.     // Finished loop, do nothing
6. }

Parsed in 0.053 seconds, using GeSHi 1.0.8.4

Extra check against 0, or no check at all, hmm... Of course exception handling isn't cheap, but if you're worried about optimizing a loop, it's likely being executed pretty darn often anyway.

Congratulations, that has to be the worst use of exceptions ever. Absolutely horrible.

I would have thought this is quickest

Code: Select all

try {
while(true) {
...
i++}
} catch (ArrayIndexOutOfBounds e) {
//blah
}


quick but would only use on LARGE arrays.

NB wouldn't use this in j2me as alot of shit VMs don't take to any sort of exception well.

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