Java: how to create a variable that only allows 3 different values

Question

How to create a variable that only allows 3 different values ? For example, the variable color can only take either one of the 3 values {RED, BLACK, ORANGE} and nothing else.

Obviously, I know that I can define String color , but is there a better way to do this ?

possible duplicate of [What are enums and why are they useful?](http://stackoverflow.com/questions/4709175/what-are-enums-and-why-are-they-useful) — Andy Brown, Jan 15 '15 at 14:55

score 6 · Accepted Answer · answered Jan 15 '15 at 14:47

6

Define an enum

public enum Color {
   RED, BLACK, ORANGE;
}

and use it like this:

Color red = Color.RED;

You can define in or outside of the enclosing class.

If you wish to define it inside the class, the enum will be implicitly static (by default) and will be accessible it like this

SomeClass.Color red = SomeClass.Color.RED;

answered Jan 15 '15 at 14:47

Konstantin Yovkov

62,134
8
100
147

Where do I define this? Within or outside the class ? – mynameisJEFF Jan 15 '15 at 14:48
How about testing for equality ? For example, I have `Color color = RED` , should I use `color.equals(RED)` or `color == RED` to test for equality ? – mynameisJEFF Jan 15 '15 at 14:53
1

Use `==`. These are constants, so `==` should return true for `color == Color.RED`. – Konstantin Yovkov Jan 15 '15 at 14:55
1

Yes, but in this way you don't have a real `java.awt.Color` information in your `enum`. – Giulio Biagini Jan 15 '15 at 14:55
Who said that the `java.awt.Color` are needed? Read again the question – Konstantin Yovkov Jan 15 '15 at 14:56
1

== and equals() are the same, per the implementation in the enum class: ` public final boolean equals(Object other) { return this==other; }` – Zéychin Jan 15 '15 at 14:58
I don't know, because is neither told nor not been told. – Giulio Biagini Jan 15 '15 at 15:01
Wait, how would the answer differ if I needed `java.awt.Color` ? – mynameisJEFF Jan 15 '15 at 15:03
If you need only three constants from `java.awt.Color`, you can see the answer of @Guilio – Konstantin Yovkov Jan 15 '15 at 15:05

score 0 · Answer 2 · answered Jan 15 '15 at 14:50

0

You can use an Enum. It allows only to use specific Objects.

Enum Color { RED, GREEN, BLUE };
Color var = Color.RED;

answered Jan 15 '15 at 14:50

kostja93

3
2

Giulio Biagini · Answer 3 · 2015-01-15T14:59:08.577

If you want a simple way to define a color with no particular meaning:

public enum Color {
    RED, BLACK, ORANGE;
}

If you want to define a variable which can allows real java.awt.Color:

import java.awt.Color;


public enum MyColor
{
    RED (Color.RED),
    BLACK (Color.BLACK),
    ORANGE (Color.ORANGE);


    private Color value;

    private MyColor(Color value) {
        this.value = value;
    }

    public Color getValue() {
        return value;
    }
}

score 0 · Answer 4 · answered Jan 15 '15 at 15:06

Enum-variables/fields can hold null aswell, so you will have 4 possible values, BLACK,RED,ORANGE and null. Try to use null as BLACK.

enum Color {RED,ORANGE;
  static boolean isBlack(Color c){
    return c == null;
  }
  static boolean isRed(Color c){
    return c == RED;
  }
  static boolean isOrange(Color c){
    return c == ORANGE;
  }
};

Java: how to create a variable that only allows 3 different values

4 Answers4