无法从ArrayList中删除 [英] Not able to remove from an ArrayList

问题描述

 import java.util;  
 class Driver{

 public static void main(String[] args) {
      ArrayList<String> lstStr = new ArrayList<String>();
      lsstStr.add("A");
      lsstStr.add("B");
      lsstStr.add("C");
      for(Iterator<String> it = lstStr.Iterator(); it.hasNext();)
      {
          str = it.next();
          if(str.equals("B")){lstStr.remove(str);}
      }
      for(Iterator<String> it = lstStr.Iterator(); it.hasNext();)
      {
        System.out.println(it.next());
      }
 }
 }

这不是删除B 从列表中。当循环第二次运行时为什么Str不等于B。为什么？

This is not removing "B" from the list. Why Str is not equal to "B" when loop runs second time.Why?

推荐答案

你不能从中删除一个项目你正在使用除之外的集合％29rel =nofollow> Iterator.remove - 您将获得 ConcurrentModificationException 。所以你的循环将是这样的：

You can't remove an item from a collection you're iterating over except using Iterator.remove - you'll get a ConcurrentModificationException. So your loop would be something like:

for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {
    String value = iterator.next();
    if (value.equals("B")) {
        iterator.remove();
    }
}

当然，你应该使用 removeAll 到只是删除具有特定值的所有项目 - 但如果您需要根据除简单相等之外的某些条件删除，则使用上述方法（例如， 删除长度大于5的所有值。另一个选项是收集要在新集合中删除的所有值，然后再调用 removeAll 。

Of course, you should use removeAll to just remove all items with a specific value - but the above approach is the one to use if you need to remove based on some condition other than simple equality (e.g. "remove all values with a length greater than 5". Another option is to collect all the values to remove in a new collection, and then call removeAll afterwards.

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