java - 参数化 Java 枚举

Question

如何在 Java 中参数化一个或多个 enum 值？

我有 3 个非常相似的 enum: ActiveStateGreenRed, ActiveStateGreenOrange 和 ActiveStateGreenYellow。

如何制作“通用”enum(我们称之为ActiveState)和“继承”enum:

ActiveStateGreenRed = ActiveState(STATE_COLOR.RED)

ActiveStateGreenOrange = ActiveState(STATE_COLOR.ORANGE)

public enum ActiveStateGreenRed {
    INACTIVE(false, STATE_COLOR.RED), //the only difference between enums
    ACTIVE(true, STATE_COLOR.GREEN);

    private final Boolean value;
    private final STATE_COLOR color;

    private ActiveStateGreenRed(Boolean value, STATE_COLOR color) {
        this.value = value;
        this.color = color;
    }

    public Boolean toValue() {
        return value;
    }

    public STATE_COLOR toColor() {
        return color;
    }
}

Answer 1

enum 无法继承。你可以做类似的事情:

public enum ActiveState {
  INACTIVE_RED(false, STATE_COLOR.RED), //the only difference between enums
  ACTIVE_RED(true, STATE_COLOR.RED),

  INACTIVE_GREEN(false, STATE_COLOR.GREEN),
  ACTIVE_GREEN(true, STATE_COLOR.GREEN);

  ...
}

或者，采用“经典”预枚举方式:

public final class ActiveState {

  public final static ActiveState ACTIVE_RED = new ActiveState( true, STATE_COLOR.RED );

  public final static ActiveState ACTIVE_GREEN = new ActiveState( true, STATE_COLOR.GREEN );

  ...

  private final Boolean value;
  private final STATE_COLOR color;

  private ActiveState(Boolean value, STATE_COLOR color) {
    this.value = value;
    this.color = color;
  }

}

一般来说，具有(包)私有(private)构造函数(仅提供预定义的常量实例)的类可以很像枚举。并且您可以使用这些类拥有继承层次结构。