How to retrieve Enum name using the id?

Question

I have the enum as:

public enum EnumStatus {

    PASSED(40L, "Has Passed"),
    AVERAGE(60L, "Has Average Marks"),
    GOOD(80L, "Has Good Marks");

    private java.lang.String name;

    private java.lang.Long id;

    EnumStatus(Long id, java.lang.String name) {
        this.name = name;
        this.id = id;
    }

    public java.lang.String getName() {
        return name;
    }

    public java.lang.Long getId() {
        return id;
    }
}

I have to get the Enum names(PASSED, AVERAGE, GOOD) using the ids only(40,60, 80). How do I do it?

Answer 1

Create a static method in your enum which searches in values (implicit method/member, don't know exactly which is it) and returns the corresponding value. For cases in which the method can not find a matching value, you should create a special entry, e.g. UNKNOWN, which you can return. This way, you do not have to return null, which is always a bad idea.

public static EnumStatus getById(Long id) {
    for(EnumStatus e : values()) {
        if(e.id.equals(id)) return e;
    }
    return UNKNOWN;
}

Btw - your code seems to be wrong. The bracket after GOOD seems to not belong there.

Answer 2

This can be done using a static map along with a static initializer:

public enum EnumStatus {

    PASSED(40L, "Has Passed"),
    AVERAGE(60L, "Has Average Marks"),
    GOOD(80L, "Has Good Marks");

    private static final Map<Long, EnumStatus> byId = new HashMap<Long, EnumStatus>();
    static {
        for (EnumStatus e : EnumStatus.values()) {
            if (byId.put(e.getId(), e) != null) {
                throw new IllegalArgumentException("duplicate id: " + e.getId());
            }
        }
    }

    public static EnumStatus getById(Long id) {
        return byId.get(id);
    }

    // original code follows

    private java.lang.String name;

    private java.lang.Long id;

    EnumStatus(Long id, java.lang.String name) {
        this.name = name;
        this.id = id;
    }

    public java.lang.String getName() {
        return name;
    }

    public java.lang.Long getId() {
        return id;
    }

}

This will give an O(1) getById() method, and will automatically detect if you accidentally have duplicate ids in the enum.

Answer 3

You make this work as follows:

public static String fromId(long id) {
        for (EnumStatus es : EnumStatus.values()) {
            if (es.id.equals(id)) {
                return es.getName();
            }
        }
        throw new IllegalArgumentException();
}