14.6. Enumeration Pattern

The enumeration pattern, where specific instances of a Java class represent the allowed values in an enumeration, is a useful programming technique in Java to constrain the values that can be assigned to a field.

As an example of this pattern, the following code snippet shows how the enumeration pattern can be used to represent the allowable eye colors for a person:

public class Person {

  private EyeColor eyes = Color.BLUE;

  /* Rest of code not shown */
}

public class EyeColor {

  public static EyeColor BLUE  = new Color("blue");
  public static EyeColor BROWN = new Color("brown");

  private String color;

  private EyeColor(String color) {

    this.color = color;
  }
}

JDO 2.0 may add explicit support for this pattern so that applications can use enumerations as fields of persistent objects.