Can i define an final String[][] with some other final String[]s?

Question

i defined some final String arrays and initial them at another place, now i want to make it easier to traverse them, so maybe i need to put them in a final String[][] ,

  private static final String[] a,b,c,d;
  private static final String[][] all = {a,b,c,d};

but it give me errors

The blank final field a may not have been initialized

now i know the final variable should be assigned before used but i have no idea to solve my problem, is there any way to traverse a,b,c,d easier than the following code?

  for(String s : a){};
  for(String s : b){};
  ...

BTW i want to assign by traversing them

@Oli Charlesworth orz...it seems wrong..now i initial them in a static block, there are still errors — AngryYogurt, May 11 '14 at 13:55

score 2 · Accepted Answer · answered May 11 '14 at 13:49

As long as you know the size of a through d, you can initialize them when you declare them:

private static final String[] a = new String[YOUR_VALUE_HERE], 
                              b = new String[YOUR_VALUE_HERE],
                              c = new String[YOUR_VALUE_HERE],
                              d = new String[YOUR_VALUE_HERE];
private static final String[][] all = {a,b,c,d};

You can still initialize the contents of the arrays later, since only the array reference itself is final.

Also I gues you can use a `static` initializer block: static `{ /*init arrays here*/ }` — user3001, May 11 '14 at 14:38

score 0 · Answer 2 · edited May 23 '17 at 11:50

If you want to have static and final arrays, I suggest you to use singleton patten with only accessors. That way you have one instance (static) and those arrays can't be changed on another (final).

public class ArrayContainer {
    private ArrayContainer instance = new ArrayContainer();
    private static final int SIZE_A = 1;
    private static final int SIZE_B = 2;
    private static final int SIZE_C = 3;
    private static final int SIZE_D = 4;
    private static String[] a, b, c, d;
    private static String[][] all;

    private ArrayContainer() {
        a = new String[SIZE_A];
        b = new String[SIZE_B];
        c = new String[SIZE_C];
        d = new String[SIZE_D];
        all = new String[][]{a, b, c, d};
    }

    public String[] getA(){
        return a;
    }

    public String[] getB(){
        return b;
    }

    public String[] getC(){
        return c;
    }

    public String[] getD(){
        return d;
    }

    public String[][] getAll(){
        return all;
    }
}

Anyway you should remember that final array is not immutable. If you would like to have immutable I suggest you read this: Immutable array in Java.

Still you can also add only getters like

public String get(int array, int index){
    return all[i][y];
}

Artur Malinowski · Answer 3 · 2014-05-11T14:31:34.963

0

If you need to init your static fields, use static block:

static final String[] a;
static {
    // put all the logic here
    // and assign final var at the end
    a = new String[17];
}
static final String[][] all = {a};

Remember also, that order in example above is important. Declaration of all array before initialization of a would cause The blank final field a may not have been initialized error.

edited May 11 '14 at 14:31

answered May 11 '14 at 14:15

Artur Malinowski

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Can i define an final String[][] with some other final String[]s?

3 Answers3