非法正向参考和枚举 [英] Illegal Forward Reference and Enums

问题描述

我在Java中编程一个游戏，它由一个瓦片组成。我不能无意地界定瓦片的边缘，以及它们如何相互关联，例如要得到一个瓦片的相对边缘，我想要能够输入 TOP.opposite（）。然而，当使用枚举来定义这些边，我最终必须在构造函数中转发至少两个参考：

  public enum Edge {
 
 TOP（Edge.BOTTOM），//非法转发参考
 BOTTOM（Edge.TOP），
 LEFT（Edge.RIGHT），//非法转发参考
 RIGHT（Edge.LEFT）; 
 
私人边对面; 
 
私人边缘（Edge opp）{
 this.opposite = opp; 
} 
 
 public Edge对（）{
 return this.opposite; 
} 
} 
  

有没有办法使用枚举来解决这个问题这是一样的简单？

解决方案

你可以做到这一点不直观。

  public enum Edge {
 TOP，BOTTOM，LEFT，RIGHT; 
私人边对面; 
 
 static {
 TOP.opposite = BOTTOM; 
 BOTTOM.opposite = TOP; 
 LEFT.opposite = RIGHT; 
 RIGHT.opposite = LEFT; 
} 
 public Edge对（）{
 return this.opposite; 
} 
} 
  

I'm programming a game in java which is made up of a grid of tiles. I wan't to be able to inuitively define the edges of the tiles and how they relate to each other, e.g. to get the opposite edge of a tile, I want to be able to just type TOP.opposite(). However, when using enums to define these edges I end up having to forward reference at least two of them in the contstructor:

public enum Edge {

   TOP(Edge.BOTTOM), //illegal forward reference
   BOTTOM(Edge.TOP),
   LEFT(Edge.RIGHT), //illegal forward reference
   RIGHT(Edge.LEFT);

   private Edge opposite;

   private Edge(Edge opp){
      this.opposite = opp;
   }

   public Edge opposite(){
      return this.opposite;
   }
}

Is there any way of getting round this problem using enums which is just as simple?

解决方案

You can do this which is not as intuitive.

public enum Edge {
    TOP, BOTTOM, LEFT, RIGHT;
    private Edge opposite;

    static {
        TOP.opposite = BOTTOM;
        BOTTOM.opposite = TOP;
        LEFT.opposite = RIGHT;
        RIGHT.opposite = LEFT;
    }
    public Edge opposite(){
        return this.opposite;
    }
}

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