What is the difference between the two following methods of array initialization:
Object[] oArr = new Object[] {new Object(), new Object()};Object[] oArr = {new Object(), new Object()};
Is it related to heap/stack allocation?
Thanks!
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8There' no difference.Carl Manaster– Carl Manaster2011-01-16 17:21:08 +00:00Commented Jan 16, 2011 at 17:21
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"premature optimization is the root of all evil"gulbrandr– gulbrandr2011-01-16 17:27:39 +00:00Commented Jan 16, 2011 at 17:27
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@ Carl Manaster: this should be your answer.Naveed– Naveed2011-01-16 17:29:51 +00:00Commented Jan 16, 2011 at 17:29
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Thanks, @Naveed, but it's too short for an answer.Carl Manaster– Carl Manaster2011-01-16 17:37:19 +00:00Commented Jan 16, 2011 at 17:37
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5@gulbrandr: It would only be premature optimization if the OP believed them to do the same thing, and was asking which one was faster. It's not an "optimization" question when he's asking whether there are any differences between the two - if they behave differently, that's far more important than optimization.Jon Skeet– Jon Skeet2011-01-16 17:39:45 +00:00Commented Jan 16, 2011 at 17:39
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4 Answers
None at all - they're just different ways of expressing the same thing.
The second form is only available in a variable declaration, however. For example, you cannot write:
foo.someMethod({x, y});
but you can write:
foo.someMethod(new SomeType[] { x, y });
The relevant bit of the Java language specification is section 10.6 - Array Initializers:
An array initializer may be specified in a declaration, or as part of an array creation expression (§15.10), creating an array and providing some initial values:
7 Comments
Jon Skeet
@gasan: Yes, that's part of an array creation expression... I don't see how that goes against anything in my answer.
Priyanshul Govil
I think it would be better to add that inside a method,
return new SomeType[] {x, y}; is valid but return {x, y}; is invalid.Jon Skeet
@PriyanshulGovil: I don't see why it's worth highlighting return statements specifically. I've already given one example, as well as the general case of the second form being available in a variable declaration. A return statement is not a variable declaration, therefore it's invalid in that context.
Priyanshul Govil
Oh, I was seeing another question in parallel, which asked the difference between both
new SomeType[] {..} and {..} (not specifically during assignment), and I commented on the wrong question. I'm sorry.Priyanshul Govil
Although,
SomeType object = SomeFunction() is still initialization of object from a function which returns SomeType. |
Absolutely identical. The second is allowed shorthand for the first (only when, as here, it is done as part of a variable declaration.
Comments
In Java all objects live in the heap, as arrays are objects in Java they lives in the stack.
for these two there is no difference in result, you 'll got two array objects with the same elements.
However sometimes you will encounter some situations where you can't use them, for example you don't know the elements of the array. then you get stuck with this form:
Object [] array=new Object[size];
Comments
There is a small and catchy difference still!
You can do
int[] arr;
arr= {1,2,3}; // Illegal
But you can very well do
int[] arr;
arr = new [] {1,2,3} //Legal
Also if you are to initialize later then you cannot do
int arr;
arr = new [] {1,2,3} //Illegal
