Can I declare and initialize an array with the same instruction in Java?

问题

Is there a way to do the following at the same time?

static final int UN = 0; // uninitialized nodes
int[] arr;

// ... code ...

arr = new int[size];
for (int i = 0; i < 5; i++) {
    arr[i] = UN;
}

Basically, I want to declare arr once I know what its size will be and initialize it to UN without having to loop. So something like this:

int[] arr = new int[size] = UN;

Is this possible?

Thanks.

回答1:

No, not with the standard libraries. If you write your own functions, though, you can easily do so in a single statement (not instruction; those are different). Mine looks like String[][] strings = Arrayu.fill(new String[x][y], "");

Here's a link. There's some junk in there too, though; I just posted a copy of the current source directly without cleaning it up.

回答2:

Arrays.fill(arr, UN);

回答3:

You don't need to initialize them with 0. An int defaults to 0 already.

Just

int[] array = new int[size];

is enough. It gives you an array of zeroes of the given length. If it were an Integer[], it would have been an array of nulls.

回答4:

Well, in the case of objects (or primitives with autoboxing) you can do the following:

int count = 20;
final int UN = 0;
Integer[] values = Collections.nCopies(count, UN).toArray(new Integer[count]);

The downsides are that you have to use the object forms of the primitives (since the Collections must be of objects) and a separate List will be constructed and then thrown away. This would allow you to create the array as one statement however.

回答5:

No.

Next question?

回答6:

int arr[] = { 0, 0, 0, 0, 0 };

回答7:

Oops, read your question better:

You can init an array like so

int[] arr = new int[] {UN, UN, UN, UN, UN};

But ofcourse, if you don't know the size at compile time, then you have to do the for loop. The second technique is not possible.

来源：https://stackoverflow.com/questions/3426668/can-i-declare-and-initialize-an-array-with-the-same-instruction-in-java