如何在Comparator中处理null比较方法参数? [英] How to handle null compare method arguments in Comparator?

问题描述

我创建了Comparator<Entity>的实现，但是当我使用此比较器对Array<Entity>进行排序时.我将收到一个java.lang.NullPointerException，因为当我将该实体映射到一个已被删除的静态集合时，会出现.现在我的问题是我不知道返回什么来跳过compare方法.

I have created an implementation of Comparator<Entity>, but when I use this comparator to sort an Array<Entity>. I will receive an java.lang.NullPointerException, because when I map the entity to a static collections which is already removed. Now my problem is I don't know what to return to skip the compare method.

public class CustomComparator implements Comparator<Entity> {

   public int compare(Entity e1, Entity e2) {
       if( e1== null || e2 == null) {
           return // don't know what to return to skip this method;
       }

       Vector2 e1Pos = Mapper.transform.get(e1).position;
       Vector2 e2Pos = Mapper.transform.get(e2).position;

   }

}

推荐答案

您无法跳过"比较.您希望排序代码做什么?您必须为其提供结果.

You can't "skip" the comparison. What would you expect the sorting code to do? You've got to provide it with a result.

共有两个选项:

• 抛出NullPointerException表示您不支持比较null值.在 文档
• 确定null排在其他所有事物之前，但等同于自身

• Throw a NullPointerException to indicate that you just don't support comparing null values. That's explicitly an option in the compare documentation
• Decide that null comes before everything else, but is equal to itself

后一种实现类似于:

public int compare(Entity e1, Entity e2) {
    if (e1 == e2) {
        return 0;
    }
    if (e1 == null) {
        return -1;
    }
    if (e2 == null) {
        return 1;
    }
    Vector2 e1Pos = Mapper.transform.get(e1).position;
    Vector2 e2Pos = Mapper.transform.get(e2).position;
    return ...;
}

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