Enums

This data structure allows defining a set of values, and assigning them to an object.

public enum NumbersEnum {

    /**
     * First enum value.
     */
    ONE,
    /**
     * Third enum value.
     */
    THREE,
    /**
     * Second enum value.
     */
    TWO

}

NumbersEnum number = NumbersEnum.TWO;

Enums as Classes

Java enums work similar to any class, which means they can implement interfaces, and contain custom methods.

Enums as Data Structures

As they are similar to other classes they can be used to create data structures, for example each value may contain a String:

public enum StringEnum
{

   VALUE("StringValue")

   private String content;

   private StringEnum(final String content)
   {
      this.content = content;
   }

   public String getContent()
   {
      return content;
   }

}

As enum constructors should be private, there is no way to create a value which is not contained in the enum.

Switchs

Enums are easy to use in switchs:

public void checkValue(final NumbersEnum value) {
   switch(value) {
   case ONE:
      // Code
      break;
   case TWO:
      // Code
      break;
   default:
   }
}

Finding Values

Enums contain all the fields defined on them, and these can be acquired easily:

NumbersEnum.values();

Working with the ordinal value is not recommended, as this will change of the fields are reordered:

NumbersEnum.TWO.ordinal();

It is better using the string value:

final NumbersEnum numbers = NumbersEnum.valueOf("TWO");

More Information

• Enum Types