Get Enum instance

Question

I have an Enum:

public enum Type {

    ADMIN(1), 
    HIRER(2), 
    EMPLOYEE(3);

    private final int id;

    Type(int id){
        this.id = id;       
    }

    public int getId() {
        return id;
    }
}

How can I get a Type enum passing an id property?

You could iterate the `Type` values and look for your `id`; or populate a `Map`. — Elliott Frisch, May 03 '16 at 15:27
[This might be exactly what you need.](http://stackoverflow.com/a/2965252/1682559) (except that you have an `int id` instead of a `String text`. — Kevin Cruijssen, May 03 '16 at 15:30

score 8 · Answer 1 · answered May 03 '16 at 15:31

8

You can build a map to do this lookup.

static final Map<Integer, Type> id2type = new HashMap<>();
static {
    for (Type t : values())
        id2type.put(t.id, t);
}
public static Type forId(int id) {
    return id2type.get(id);
}

answered May 03 '16 at 15:31

Peter Lawrey

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I like this solution the most. It is clean and has the best performance for arbitrarily big enums. – brimborium May 03 '16 at 15:59

score 2 · Answer 2 · edited May 23 '17 at 12:08

2

Create a method inside the Type class returning the Enum instances:

Type get(int n) {
    switch (n) {
    case 1:
        return Type.ADMIN;
    case 2:
        return Type.EMPLOYEE;
    case 3:
        return Type.HIRER;
    default:
        return null;
    }

}

TIP: you need to add default in switch-case or add a return null at the end of the method to avoid compiler errors.

UPDATE (thanks to @AndyTurner):

It would be better to loop and refer to the id field, so you're not duplicating the IDs.

Type fromId(int id) {
    for (Type t : values()) {
        if (id == t.id) {
            return t;
        }
    }
    return null;
}

edited May 23 '17 at 12:08

Community

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1

answered May 03 '16 at 15:29

Jordi Castilla

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2

It would be better to loop and refer to the `id` field, so you're not duplicating the IDs. – Andy Turner May 03 '16 at 15:30
@AndyTurner updated answer... but... why you say I'm duplicating the id's? I'm missing something? or you mean write a line by each id?? – Jordi Castilla May 03 '16 at 15:35
I mean that if you want to change the id for `ADMIN`, you'd have to change it in two places (the instance declaration and the switch). – Andy Turner May 03 '16 at 15:39
ohhhhhhhhhhhh.... touché! ^_^ – Jordi Castilla May 03 '16 at 15:40
It would be even better to populate a `Map` that is filled in the constructor and then just look up the id... – brimborium May 03 '16 at 15:57
1

@brimborium yes, but that is Peter answer.... – Jordi Castilla May 03 '16 at 15:58
1

@JordiCastilla I just saw. ;) – brimborium May 03 '16 at 15:59
1

Note: every time you call `values()` it creates a new array of the enum values. It has to do this because it doesn't know if you are going to mutate it or not. – Peter Lawrey May 03 '16 at 16:14

score 0 · Accepted Answer · answered May 03 '16 at 16:06

0

Try this out. I have created a method which searches type using id:

public static Type getType(int id) {

    for (Type type : Type.values()) {
        if (id == type.getId()) {
            return type;
        }
    }
    return null;
}

answered May 03 '16 at 16:06

Anand Kulkarni

87
5

Get Enum instance

3 Answers3