Hierarchical enum in Java

Question

Let's say I have a structure like this:

Is it possible to create an enum that will return the string value of selected cell? For example:

enum.GROUP_MAIN1.SUBGROUP1.COL1

will return value "COL1".

I was looking for nested enums but didn't find the solution to this situation.

Answer 1

You can do this with such trick:

public interface GROUPMAIN1 {
    enum SUBGROUP1 implements GROUPMAIN1 {
        COL1,
        COL2,
        COL3
    }
    enum SUBGROUP2 implements GROUPMAIN1 {
        COL3,
        COL4
    }
}

So to get enum you will need to use GROUPMAIN1.SUBGROUP1.COL1.

It can also be done in another way if all you need is just a string constants:

public interface GROUPMAIN1 {
    interface SUBGROUP1 {
        String COL1 = "COL1";
        String COL2 = "COL2";
    }
    interface SUBGROUP2 {
        String COL3 = "COL3";
        String COL4 = "COL4";
    }
}

Answer 2

You cannot have everything you ask for. Here’s one way of getting some of it:

enum MainGroup { GROUP_MAIN1, GROUP_MAIN2 };

enum Subgroup {
    SUBGROUP1(MainGroup.GROUP_MAIN1), SUBGROUP2(MainGroup.GROUP_MAIN1),
    SUBGROUP3(MainGroup.GROUP_MAIN2), SUBGROUP4(MainGroup.GROUP_MAIN2);

    MainGroup main;

    private Subgroup(MainGroup main) {
        this.main = main;
    }

    public MainGroup getMainGroup() {
        return main;
    }

}

enum Col {
    COL1(Subgroup.SUBGROUP1), COL2(Subgroup.SUBGROUP1), COL3(Subgroup.SUBGROUP2), COL4(Subgroup.SUBGROUP2),
    COL5(Subgroup.SUBGROUP3), COL6(Subgroup.SUBGROUP3), COL7(Subgroup.SUBGROUP4), COL8(Subgroup.SUBGROUP4);

    Subgroup sub;

    private Col(Subgroup sub) {
        this.sub = sub;
    }

    public MainGroup getMainGroup() {
        return sub.getMainGroup();
    }

    public Subgroup getSubgroup() {
        return sub;
    }
}

You may also implement a method in MainGroup to find all subgroups under that main group, and the same for subgroups and cols.