How to get Enum Value from index in Java?

Question

I have an enum in Java:

public enum Months
{
    JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC
}

I want to access enum values

Answer 1

I recently had the same problem and used the solution provided by Harry Joy. That solution only works with with zero-based enumaration though. I also wouldn't consider it save as it doesn't deal with indexes that are out of range.

The solution I ended up using might not be as simple but it's completely save and won't hurt the performance of your code even with big enums:

public enum Example {

    UNKNOWN(0, "unknown"), ENUM1(1, "enum1"), ENUM2(2, "enum2"), ENUM3(3, "enum3");

    private static HashMap enumById = new HashMap<>();
    static {
        Arrays.stream(values()).forEach(e -> enumById.put(e.getId(), e));
    }

    public static Example getById(int id) {
        return enumById.getOrDefault(id, UNKNOWN);
    }

    private int id;
    private String description;

    private Example(int id, String description) {
        this.id = id;
        this.description= description;
    }

    public String getDescription() {
        return description;
    }

    public int getId() {
        return id;
    }
}

If you are sure that you will never be out of range with your index and you don't want to use UNKNOWN like I did above you can of course also do:

public static Example getById(int id) {
        return enumById.get(id);
}