How to randomize enum elements?

Question

Say you have an enum with some elements

public enum LightColor {
   RED, YELLOW, GREEN
}

And would like to randomly pick any color from it.

I put colors into a

public List<LightColor> lightColorChoices = new ArrayList<LightColor>();

lightColorChoices.add(LightColor.GREEN);
lightColorChoices.add(LightColor.YELLOW);
lightColorChoices.add(LightColor.RED);

And then picked a random color like:

this.lightColor = lightColorChoices.get((int) (Math.random() * 3));

All of this (while working fine) seems needlessly complicated. Is there a simplier way to pick a random enum element?

as your fellow developer for a random number ? ... sorry, no. — ic3, Nov 13 '11 at 19:50
related question: http://stackoverflow.com/questions/5269250/random-value-from-enum-with-probability — Ray Tayek, Nov 17 '11 at 17:43
I think this one is more akin to the problem at hand (hint: look for trashgod's answer): http://stackoverflow.com/questions/1972392/java-pick-a-random-value-from-an-enum — DPM, Feb 12 '12 at 22:55

Lucas · Accepted Answer · 2016-07-23T17:24:37.057

24

Java's enums are actually fully capable Objects. You can add a method to the enum declaration

public enum LightColor {
    Green,
    Yellow,
    Red;

    public static LightColor getRandom() {
        return values()[(int) (Math.random() * values().length)];
    }
}

Which would allow you to use it like this:

LightColor randomLightColor = LightColor.getRandom();

edited Jul 23 '16 at 17:24

answered Nov 13 '11 at 19:51

Lucas

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Thank you!, it works like a charm!!! – Taber Feb 10 '14 at 16:21

score 8 · Answer 2 · edited Nov 13 '11 at 21:12

8

LightColor random = LightColor.values()[(int)(Math.random()*(LightColor.values().length))];

edited Nov 13 '11 at 21:12

Nightfirecat

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answered Nov 13 '11 at 19:51

b_erb

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Rich O'Kelly · Answer 3 · 2011-11-14T09:15:16.020

5

Use Enum.values() to get all available options and use the Random.nextInt() method specifying the max value. eg:

private static Random numberGenerator = new Random();
public <T> T randomElement(T[] elements)
  return elements[numberGenerator.nextInt(elements.length)];
}

This can then be called as such:

LightColor randomColor = randomElement(LightColor.values());

edited Nov 14 '11 at 09:15

answered Nov 13 '11 at 19:51

Rich O'Kelly

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+1 for suggesting Random.nextInt() instead of multiplying by size – Jorn Nov 13 '11 at 21:38

score 3 · Answer 4 · answered Nov 13 '11 at 19:51

3

This should be just easy as shown below

LightColor[] values = LightColor.values();
LightColor value = values[(int) (Math.random() * 3)];

answered Nov 13 '11 at 19:51

Kowser

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score 0 · Answer 5 · answered Apr 09 '14 at 15:14

So reading Kowser's answer, I came up with something here. Given an enum ChatColor containing different colors, you could do the following:

private ChatColor getRandomColor() {
    ChatColor randomColor = ChatColor.values()[random.nextInt(ChatColor
            .values().length - 1)];
    ChatColor[] blacklist = { ChatColor.BOLD, ChatColor.ITALIC,
            ChatColor.MAGIC, ChatColor.RESET, ChatColor.STRIKETHROUGH,
            ChatColor.UNDERLINE };
    while (Arrays.asList(blacklist).contains(randomColor)) {
        randomColor = ChatColor.values()[random
                .nextInt(ChatColor.values().length)];
    }
    return randomColor;
}

and even have a blacklist.

score 0 · Answer 6 · answered Nov 13 '11 at 19:50

0

You could associate an integer id to each enum color, and have a valueOf(int id) method that returns the corresponding color. This will help you get rid of the list..

Tiberiu

answered Nov 13 '11 at 19:50

jumping-jack

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How to randomize enum elements?

6 Answers6

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