java enum with array attribute

Question

I see that obviously java does not allow to pass arrays directly to methods (didn't know this before). For example this does not compile:

public static void main(String[] args) {
    testFunk({1,2,3,4});
}

public static void testFunk(int[] a) {}

But this does:

public static void main(String[] args) {
    int[] a = {1,2,3,4};
    testFunk(a);
}

public static void testFunk(int[] a) {}

But what if i need to create an enum with a constructor that accepts an array?

For example I tried the following code, but it does not compile for the same reason as above:

    public enum FigureType {

    SQUARE({{true, true},{false, false}});

    private boolean[][] matrix;

    private FigureType(boolean[][] matrix) {
        this.matrix = matrix;
    }

}

Unfortunately there does not seem to be a simple workaround here. The only option that comes to my mind is to build something like this:

    public enum FigureType {

    SQUARE(() -> {boolean[][] array = {{true,true},{false,false}}; return array; });

    private boolean[][] matrix;

    private FigureType(Supplier<boolean[][]> supplier) {
        this.matrix = supplier.get();
    }

}

But this looks quite ugly ... is there some better solution?

Thanks and greetings, Daniel

khelwood · Accepted Answer · 2017-12-14 14:44:54Z

10

You can pass arrays directly to methods. If you want to initialise an array and pass it to a method in one line, you need this:

testFunk(new int[] {1,2,3,4});

instead of this

testFunk({1,2,3,4});

answered Dec 14, 2017 at 14:44

khelwood

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GhostCat · Accepted Answer · 2017-12-14 14:47:11Z

1

If providing array values as literals is your primary concern you could use:

varargs / ellipsed: boolean...
make the parameter a list and use Arrays.asList()

As well.

answered Dec 14, 2017 at 14:47

GhostCat

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Lino · Accepted Answer · 2017-12-14 14:52:16Z

1

You can initialize the array directly inline with the new keyword:

public enum FigureType {

    SQUARE(new boolean[][]{{true, false}, {false,true}});

    FigureType(boolean[][] array){ ... }

}

To mention is that inside a 2D array the short array initializer ({}) can be used.

answered Dec 14, 2017 at 14:52

Lino

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Rajan Singh · Accepted Answer · 2017-12-14 15:09:31Z

0

By passing a list of elements as a parameter does not makes sense until you wrap in some structure(object) and initialize that through the new operator.

So, instead of : SQUARE({{true, true},{false, false}});

Do : SQUARE(new boolean[][] {{true, true},{false, false}});

answered Dec 14, 2017 at 15:09

Rajan Singh

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