Java - Declaring Arrays

Question

When I create a new array, I do something like this.

int[] anArray = {1, 2, 3};

But I've seen some people do something like.

int[] anArray = new int[] {1, 2, 3};

I understand what it does, but I don't understand the purpose of it. Is there a benefit of doing it one way over another?

Thanks

Answer 1

There's no difference in behaviour where both are valid. They are covered in section 10.6 and 15.10 of the Java language specification.

However the first syntax is only valid when declaring a variable. So for example:

 public void foo(String[] args) {}

 ...

 // Valid
 foo(new String[] { "a", "b", "c" };

 // Invalid
 foo({"a", "b", "c"});

As for the purpose - the purpose of the first syntax is to allow variable declarations to be more concise... and the purpose of the second syntax is for general-purpose use as an expression. It would be odd to disallow the second syntax for variable declarations, just because the more concise syntax is available.

Answer 2

One would use the second way, if the declaration should be done before the initialization.

int[] arr;
arr = { 2, 5, 6, 12, 13 };

Would not work, so you use:

int[] arr;
arr = new int[]{ 2, 5, 6, 12, 13 };

instead. Another way is to declare another variable:

int[] arr;
int[] tmparr = { 2, 5, 6, 12, 13 };
arr = tmparr;

So if you don't need to seperate the declaration from the initialization, it's only a matter of clean code (use either one consistently).

Answer 3

They are almost the same thing, but the first is applicable for object assignment like:

int[] anArray = {1, 2, 3};

The other one is more globaly like

callingMyMethod(new Object[]{object1,object2});

The wrong syntax would be

callingMyMethod({object1,object2});

Let's take it further

These initialization are right:

Object[] objeto={new Object(), new Object()};
Object[] objeto=new Object[]{new Object(), new Object()};

Also right:

Object[] objeto;
objeto=new Object[]{new Object(), new Object()}

But as Jon suggested this is wrong:

Object[] objeto;
objeto={new Object(), new Object()};

Why? Array Initializer And Array Creation Expression

Anyway both of your syntax are correct. There is no benefit on one against the other.

Interesting reading on this subject:

Arrays on Oracle Official documentation

This have also been covered on this thread