Java 枚举静态最终实例变量

Question

万岁!

这段代码工作了一段时间，然后我决定添加一种默认颜色，然后它就停止工作了。我收到以下错误:

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

在编译时使用以下代码。

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;
  }
}

据我所知，这应该可以工作，但无论出于何种原因，Java 决定抛出一个错误。有什么想法吗？

Answer 1

defaultColor 只会在调用构造函数后 进行初始化 - 因此在此之前它将具有默认值 (null)。一种选择是将默认颜色放入嵌套类型中:

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;
  }
}

当然，如果您只在代码中引用默认颜色一次，您不妨在构造函数调用中对其进行硬编码:

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