Why int[] a = new int[1] instead of just int a?

Question

Is there some hidden meaning in this code which I don't see in java? How can it be useful?

int[] a = new int[1];

than just

int a;

because from my point of view it's the same?

Answer 1

int a

defines a primitive int.

int[] a = new int[1];

defines an array that has space to hold 1 int.

They are two very different things. The primitive has no methods/properites on it, but an array has properties on it (length), and methods (specifically its on clone method, and all the methods of Object).

Arrays are a bit of a weird beast. They are defined in the JLS .

In practice, it would make sense to do this when you need to interact with an API that takes an array and operates on the results. It is perfectly valid to pass in a reference to an array with 0, 1, or n properties. There are probably other valid reasons to define an array with 1 element.

I can't think of any use cases where you would want to define an array with one element, just to bypass the array and get the element.

Answer 2

One is on the stack, one is on the heap.

Answer 3

One difference is that you can write a method that changes its int argument by changing arg[0] . This trick is used quite a bit in some of the code I've seen. It allows you to, for instance, return a boolean indicate success or failure and an int value that serves some other purpose. Without that trick, you'd have to return some sort of object containing the two values.

Answer 4

int a;

defines a variable that can hold an int

int[] a;

defines a variable that can hold an array of int

int[] a = new int[1];

does that above but also initializes it by actually creating an array (of size 1 - it can hold 1 int) and defines the variable a to hold that array, but doesn't define what's in the array.

int[] a = new int[1]{1};

does that above but also defines what's in the array: the int 1.

I suppose it does a similar thing, in that space is allocated for 1 int, but the array also defines an array. I suppose you could say these are similar:

int a = 1;
int b = a + 1;
// now b == 2

int[] a = new int[1]{1};
int b = a[0] + 1;   
// now b == 2

Answer 5

An array of size one is not the same thing as a single integer.

Even if they carry the same information, they are different types, so you can use them in different contexts.

For example, if you have a function which performs a function on all elements of an array but you want to compute it only on one value, you should pass a int[1], because the function expects an array and wants to know how many values it should process.

Answer 6

All arrays in java are objects. when declaring: int x = 5; you're declaring a primitive type.

When declaring int[] x = new int[]; you're creating an object with type int[] .

So int[] is actually a class.

Answer 7

It is used when you need to pass a primitive data type by reference.

See this .