I have the following two diffetent ways of declaring an integer array in Java, one works and one doesn't, why?

Question

The following is first way of declaring, and it worked:

static final int N = 9;
public static int[] arr = new int[N];

This is the one that doesn't:

static final int N = 9;
int arr[];    //declaring array
arr = new int[N];  // allocating memory to array

Eclipse gave me the error reminder on the second line that I don't quite get it: Syntax error on token ";", , expected

Thank you for taking the time reading my question, any advice will be much appreciated.

What part is not clear? The first is legal Java. The second is not legal. Specifically, `arr = new int[N];` is **not** in a constructor, method, or initialization block. Also, `int arr[]` is **not** `static` or `final` (but it isn't necessary for `arr` to be `static` or `final` in your first example). — Elliott Frisch, Oct 12 '19 at 06:48
@ElliottFrisch Thanks for the advice. I learnt the second part from a tutorial website. I wonder is there any circumstance that I can use "arr = new int [N];" to declare an array? — Zhiyuan Wan, Oct 12 '19 at 07:06

score 5 · Answer 1 · answered Oct 12 '19 at 06:49

5

From the public keyword in your first example, I'm guessing this appears directly inside a class definition.

arr = new int[N]; is executable code and executable code can't appear directly inside a class definition. Depending on whether it needs to be static, you have to put it either inside a constructor or inside a static initializer block.

answered Oct 12 '19 at 06:49

NPE

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Thanks! they are appearing inside a class definition, I will check out the ways you suggested to fix this. – Zhiyuan Wan Oct 12 '19 at 07:03

score 1 · Answer 2 · answered Oct 12 '19 at 07:12

As I mentioned in my initial comment, you can use that syntax in an initialization block (or a constructor). Like,

int arr[];    //declaring array
{
    arr = new int[N];   // allocating memory to array
}

or

public class MyClass {
    static final int N = 9;
    int arr[];    //declaring array
    public MyClass() {
        super();
        arr = new int[N];  // allocating memory to array
    }
}

Note that the two examples here are actually the same in byte-code. Initialization blocks (and statements) are copied by the compiler into constructors (including the default constructor) - basically as seen here.

I have the following two diffetent ways of declaring an integer array in Java, one works and one doesn't, why?

2 Answers2