通过索引从集合获取值的最佳方式 [英] Best way to get value from Collection by index

问题描述

通过索引从java.util.Collection获取值的最好方法是什么？

What is the best way to get value from java.util.Collection by index?

推荐答案

Collection 避免专门讨论索引，因为它可能对特定集合没有意义。例如， List 意味着某种形式的排序，但 Set 不会。

You shouldn't. a Collection avoids talking about indexes specifically because it might not make sense for the specific collection. For example, a List implies some form of ordering, but a Set does not.

    Collection<String> myCollection = new HashSet<String>();
    myCollection.add("Hello");
    myCollection.add("World");

    for (String elem : myCollection) {
        System.out.println("elem = " + elem);
    }

    System.out.println("myCollection.toArray()[0] = " + myCollection.toArray()[0]);

给我：

    elem = World
    elem = Hello
    myCollection.toArray()[0] = World

同时：

    myCollection = new ArrayList<String>();
    myCollection.add("Hello");
    myCollection.add("World");

    for (String elem : myCollection) {
        System.out.println("elem = " + elem);
    }

    System.out.println("myCollection.toArray()[0] = " + myCollection.toArray()[0]);

给我：

    elem = Hello
    elem = World
    myCollection.toArray()[0] = Hello

为什么要这样做？你不能只是迭代集合吗？

Why do you want to do this? Could you not just iterate over the collection?

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