如何获取java.util.Set中项的索引 [英] How to get index of an item in java.util.Set

问题描述

我知道Set和List之间的区别（允许唯一与重复，不订购/订购等）。我正在寻找的是一个保持元素排序的集合（这很容易），但我还需要能够恢复插入元素的索引。因此，如果我插入四个元素，那么我希望能够知道插入其中一个元素的顺序。

I know the differences between Set and List(unique vs. duplications allowed, not ordered/ordered, etc). What I'm looking for is a set that keeps the elements ordered(that's easy), but I also need to be able to recover the index in which an element was inserted. So if I insert four elements, then I want to be able to know the order in which one of them was inserted.

MySet<String> set = MySet<String>();
set.add("one");
set.add("two");
set.add("three");
set.add("four");

int index = set.getIndex("two");

所以在任何特定时刻我都可以检查是否已经添加了一个字符串，并获得了索引集合中的字符串。有没有这样的，或者我需要自己实现它？

So at any given moment I can check if a String was already added, and get the index of the string in the set. Is there anything like this, or I need to implement it myself?

推荐答案

<$ c $中的一个小的静态自定义方法c> Util class会有所帮助：

A small static custom method in a Util class would help:

 public static int getIndex(Set<? extends Object> set, Object value) {
   int result = 0;
   for (Object entry:set) {
     if (entry.equals(value)) return result;
     result++;
   }
   return -1;
 }

如果您需要/想要一个是的课程> 设置并提供 getIndex（）方法，我强烈建议实现一个新的 Set 并使用装饰器模式：

If you need/want one class that is a Set and offers a getIndex() method, I strongly suggest to implement a new Set and use the decorator pattern:

 public class IndexAwareSet<T> implements Set {
   private Set<T> set;
   public IndexAwareSet(Set<T> set) {
     this.set = set;
   }

   // ... implement all methods from Set and delegate to the internal Set

   public int getIndex(T entry) {
     int result = 0;
     for (T entry:set) {
       if (entry.equals(value)) return result;
       result++;
     }
     return -1;
   }
 }

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