Java Enum Static Final Instance Variables

Question

Huzzah!

This code worked for a time, then I decided to add a default color, and it stopped working. I get the following error:

1 error found:
File: Status.java  [line: 20]
Error: Status.java:20: illegal reference to static field from initializer

With the following code at compile-time.

import java.awt.Color;

enum Status
{
  OFF ("Off"),
  TRAINING ("Training", new Color(255, 191, 128)),
  BEGINNER ("Beginner", new Color(128, 255, 138)),
  INTERMEDIATE ("Intermediate", new Color(128, 212, 255)),
  ADVANCED ("Advanced", new Color(255, 128, 128));

  public final String name;
  public final Color color;

  public static final Color defaultColor = Color.WHITE;

  Status(String name)
  {
    this(name, defaultColor);
  }
  Status(String name, Color color)
  {
    this.name = name;
    this.color = color;
  }
}

This should work, as far as I can tell, but for whatever reason Java decided to throw an error. Any thoughts?

Answer 1

defaultColor will only be initialized after the constructors have been called - so it will have its default value (null) until that time. One option would be to put the default colour in a nested type:

import java.awt.Color;

enum Status
{
  OFF ("Off"),
  TRAINING ("Training", new Color(255, 191, 128)),
  BEGINNER ("Beginner", new Color(128, 255, 138)),
  INTERMEDIATE ("Intermediate", new Color(128, 212, 255)),
  ADVANCED ("Advanced", new Color(255, 128, 128));

  public final String name;
  public final Color color;

  Status(String name)
  {
    this(name, Defaults.COLOR);
  }
  Status(String name, Color color)
  {
    this.name = name;
    this.color = color;
  }

  private static class Defaults
  {
     private static Color COLOR = Color.WHITE;
  }
}

Of course, if you're only referring to the default colour once in the code, you might as well hard-code it within the constructor call:

Status(String name)
{
  this(name, Color.WHITE);
}