How to use Groovy enum

Groovy enum is very much like enum in Java, and easier to use. There are many Groovy books out there, but none of them explain it very well, so I decide to learn it by doing. This post creates an Eclipse Groovy project and write some examples to illustrate the usage of Groovy enum.

First, let's create a Groovy project:

Then create a package com.makble.testgdk and add two Groovy classes to the package.

ColorEnum.groovy

 
package com.makble.testgdk;
 
public enum ColorEnum {
    WHITE('white', 'White is mix of all colors'),
    BLACK('black', 'Black is no colors'),
    RED('red', 'Red is the color of blood')
 
    final String id;
    final String desc;
    static final Map map 
 
    static {
        map = [:] as TreeMap
        values().each{ color -> 
            println "id: " + color.id + ", desc:" + color.desc
            map.put(color.id, color)
        }
 
    }
 
    private ColorEnum(String id, String desc) {
        this.id = id;
        this.desc = desc;
    }
 
    static getColorEnum( id ) {
        map[id]
    }
}

MainTest.groovy

 
package com.makble.testgdk
 
println ColorEnum.values().size()
println ColorEnum.getColorEnum('white')
println ColorEnum.WHITE.desc
 
// values return array of all enums defined in ColorEnum
println ColorEnum.values().getClass()

The package explorer

Press Alt + Shift + X, G to run the MainTest Groovy script:

 
3
WHITE
White is mix of all colors
class [Lcom.makble.testgdk.ColorEnum;

In the enum static block, all enums were added to a map, the key is the id of the enum. Method getColorEnum can retrieve the description of the enum by its id.

The values() method returns an array of all enums defined in enum class.

You may wonder where this method was defined, you will not find it in class hierarchy. This method was defined by EnumVisitor, the class was generated dynamically and some methods and properties were added to the class, include the values() method.

The class is generated in org.codehaus.groovy.classgen.EnumVisitor.

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