在Java中使用迭代器有什么好处 [英] What are the benefits of using an iterator in Java

问题描述

我正在浏览以下代码示例：

I was browsing over the following code example:

public class GenericTest {

 public static void main (String[] args) {

  ArrayList<String> myList = new ArrayList<String>();
  String s1 = "one";
  String s2 = "two";
  String s3 = "three";

  myList.add(s1); myList.add(s2); myList.add(s3);
  String st;

  Iterator<String> itr = myList.iterator();

  while (itr.hasNext()) {
   st = itr.next();
   System.out.println(st);
  }
 }
}

我想知道什么是使用Iterator接口的实现而不是使用普通的for-each循环的好处？

I'm wondering what are the benefits of using an implementation of the Iterator interface instead of using a plain-old for-each loop?

 for ( String str : myList ) {
  System.out.println(str);
 }

如果这个例子无关紧要，我们应该什么时候会有好的情况使用迭代器？

If this example is not relevant, what would be a good situation when we should use the Iterator?

谢谢。

推荐答案

For-Each循环是在Java 5中引入的，所以它不是那么老。

The For-Each Loop was introduced with Java 5, so it's not so "old".

如果你只想迭代一个集合，你应该使用for each循环

If you only want to iterate a collection you should use the for each loop

for (String str : myList) {
   System.out.println(str);
}

但有时 hasNext（）普通旧迭代器的方法对于检查迭代器是否有更多元素非常有用。

But sometimes the hasNext() method of the "plain old" Iterator is very useful to check if there are more elements for the iterator.

for (Iterator<String> it = myList.iterator(); it.hasNext(); ) {
   String str = it.next();
   System.out.print(str);
   if (it.hasNext()) {
      System.out.print(";");     
   }
}

您也可以拨打它.remove（）删除next返回的最新元素。

You can also call it.remove() to remove the most recent element that was returned by next.

还有 ListIterator< E> ，它提供双向遍历。 next（）和 it.previous（）。

And there is the ListIterator<E> which provides two-way traversal it.next() and it.previous().

所以，它们并不等同。两者都是必需的。

So, they are not equivalent. Both are needed.

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