Returning array from method

Question

In my class, I have a method that returns an array like this.

double arrValues[] = ClassX.getValues();

I wonder that, does the array size have any influence on performance. Are there any copy operation for arrValues[] or is it only a reference return ?

Your static method really should be returning a new copy of the array (unless, possibly, if it is of length zero). — Tom Hawtin - tackline
– Tom Hawtin - tackline, Commented Oct 23, 2009 at 12:44

Asaph · Accepted Answer · 2009-10-23 07:00:26Z

3

In Java, Object types are returned by reference and primitive types are returned by value. Arrays are full blown Objects in Java. Therefore, in your example, the array is returned by reference and no copy is made.

answered Oct 23, 2009 at 7:00

Asaph

164k25 gold badges204 silver badges204 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Nader Shirazie Over a year ago

+1 for why it is a reference rather than just stating it is a reference

tangens · Accepted Answer · 2009-10-23 06:55:15Z

3

It's only a reference (like everything except the basic types long, int, short, ...) in java is a only reference).

answered Oct 23, 2009 at 6:55

tangens

39.8k21 gold badges128 silver badges140 bronze badges

Comments

Nader Shirazie · Accepted Answer · 2009-10-23 06:59:39Z

3

There's no information about the cost of constructing the array (how much that is affected by size is unknown).

Aside from that, what is returned is just a reference to the array constructed in getValues(), so the act of returning the array has no real performance impact.

answered Oct 23, 2009 at 6:59

Nader Shirazie

10.8k2 gold badges40 silver badges43 bronze badges

4 Comments

Stephen C Over a year ago

In the absence of hardware assistance, and assuming a good GC, the amortized cost of allocating an N word array is the O(N) memory writes required to zero it.

Nader Shirazie Over a year ago

I think I know what you mean, and I don't disagree. However, we don't know what the implementation of getValues() does. The "cost" I was talking about was not referring to the cost of doing "new Array[X]", rather its the cost of calculating the values that go into the array. How that scales... I don't know. However, that may not be the question the OP is asking...

penguru Over a year ago

getValues() only returns the array that is already constructed before. I wanted to ask only the cost of returning the array.

Nader Shirazie Over a year ago

Ok, cool. It is usually a good question to ask because, very often, cached array's aren't returned (because the caller can then modify it). Usually a copy of an array is returned, or a new array is constructed. These are just valuable questions to answer when looking at performance.

Collectives™ on Stack Overflow

Returning array from method

3 Answers 3

1 Comment

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related