CODEWITHSUNDEEP
performanceloopsnested-loops
os111
os111

Reputation: 154

is there a difference in the runtime of the following:

Is there a difference in the runtime of the following two snippets?

SNIPPET 1:

for ( Object obj : collection ) {
    step1( obj );
    step2( obj );
    step3( obj );
}

SNIPPET 2:

for ( Object obj : collection ) {
    step1( obj );
}

for ( Object obj : collection ) {
    step2( obj );
}

for ( Object obj : collection ) {
    step3( obj );
}

Upvotes: 0

Views: 107

Answers (6)

Crashworks
Crashworks

Reputation: 41374

Are you asking specifically about performance?

In that case, the answer depends on how fast the collection's iterator is: if Next() is an expensive operation for that particular iterator, then you pay that cost N times in the first version and 3N times in the latter. This is insignificant if your collection is a vector, but more serious when your collection is, say, an interface to some slow file I/O operation.

Upvotes: 0

Mike Dunlavey
Mike Dunlavey

Reputation: 40649

Is there any difference? Of course.

Is there a difference that matters? It all depends.

If StepN() takes a few nanoseconds, then yes. Otherwise, probably not.

Upvotes: 0

Gábor Hargitai
Gábor Hargitai

Reputation: 564

If one of your method calls will throw an exception, lets say step1 in the middle of the iteration then the second version will stop earlier than the first one. But if step3 throws an exception for the first element then the first version is faster. So the two versions are not equivalent semantically.

Upvotes: 0

Samuel Carrijo
Samuel Carrijo

Reputation: 17919

The iterations are made 3 times.

Also, you will call step1(obj) n times, then step2(obj) n times, then step3(obj) n times.

Upvotes: 0

Marco Mustapic
Marco Mustapic

Reputation: 3859

If you are asking about any language, SNIPPET 1 should be faster.

Upvotes: 0

ryeguy
ryeguy

Reputation: 66851

Of course. The first snippet iterates through the collection only once while the second snippet does it 3 separate times. The second snippet also violates the DRY principle.

Upvotes: 1

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