Java: Why can't return array using {..} without new operator?

Question

I have searched a lot on the website, but didn't find any related question. So I believe it is not a duplicate.

I know we can initialize an array with 3 ways:

• char[ ] charAr=new char[10];
• char[ ] charAr={'a', 'b', 'c'};
• char[ ] charAr=new char[]{'a','b','c'};

1st question is: what is the name of {'a','b','c'} kind of stuff? Is it called array literals?

2nd question is: what is the difference between new char[]{'a','b','c'} with {'a','b','c'}?

3rd question is: why I can't return a newly created array with {'a','b','c'}? I have to return new char[]{'a','b','c'}.

4th question: both new char[10] and new char[]{'a','b','c'} are constructors of array, right?

Answer 1

In the declaration:

char[ ] charAr={'a', 'b', 'c'};

the array {'a', 'b', 'c'} is called an array initializer. It is described in Section 10.6 of the Java Language Specification. It can only be written like that (without the new char[] in front of it) as part of a variable declaration.

In any other place (including a return statement), you need to use an array creation expression. These are described in Section 15.10 of the JLS. You can use either an array initializer or an array creation expression to initialize a variable when it is declared. That's why the new char[] appears to be optional when you declare the variable.

Regarding your 4^th question: they technically are not "constructors" (which has a specific meaning in Java terminology) but yes, they both construct arrays (or, perhaps more accurately, they both create arrays).

Answer 2

1st question is:what is the name of {'a','b','c'} kind of stuff? Is it called array literals?

No Array literals in Java, they are filling array with elements, i.e initialization.

2nd question is: what is the difference between new char[]{'a','b','c'} with {'a','b','c'}?

That first one called as * inline array declaration*.

With second you can assign it to a array which already with a defined type.

Example by me here :https://stackoverflow.com/a/19658726/1927832

3rd question is: why I can't return a newly created array with {'a','b','c'}? I have to return new char[]{'a','b','c'}.

Because in the first case the type is missing, and compiler doesn't know which type of elements they are.

4th question: both new char[10] and new char[]{'a','b','c'} are constructors of array, right?

That is creating an array of chars with specified length.