通过索引从 Collection 中获取价值的最佳方法 [英] Best way to get value from Collection by index

问题描述

通过索引从 java.util.Collection 获取价值的最佳方法是什么?

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

推荐答案

你不应该.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 暗示某种形式的排序，但 Set 不暗示.

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

虽然:

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

你为什么要这样做?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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