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问题描述

我有一个ArrayList,我想迭代。在迭代时,我必须同时删除元素。显然,这会抛出一个 java.util.ConcurrentModificationException



处理这个问题的最佳实践是什么?我应该先克隆列表吗?



我删除了不在循环中的元素,而是代码的另一部分。



我的代码如下所示:

  public class Test(){
private ArrayList< A> abc = new ArrayList< A>();
$ b $ public void doStuff(){
for(A a:abc)
a.doSomething();
}

public void removeA(A a){
abc.remove(a);


code $
$ b $ a $ doSomething 可能会调用 Test.removeA();

解决方案

两个选项:


  • 创建一个你想删除的值列表, 添加到循环内的列表,然后在最后使用 originalList.removeAll(valuesToRemove) c $ c>方法迭代器本身。请注意,这意味着您不能使用增强for循环。


    作为第二个选项的示例,删除任何字符串长度大于5的列表:

      List< String> list = new ArrayList< String>(); 
    ...
    (Iterator< String> iterator = list.iterator(); iterator.hasNext();){
    String value = iterator.next();
    if(value.length()> 5){
    iterator.remove();
    }
    }


    I have an ArrayList that I want to iterate over. While iterating over it I have to remove elements at the same time. Obviously this throws a java.util.ConcurrentModificationException.

    What is the best practice to handle this problem? Should I clone the list first?

    I remove the elements not in the loop itself but another part of the code.

    My code looks like this:

    public class Test() {
        private ArrayList<A> abc = new ArrayList<A>();
    
        public void doStuff() {
            for (A a : abc)
            a.doSomething();
        }
    
        public void removeA(A a) {
            abc.remove(a);
        }
    }
    

    a.doSomething might call Test.removeA();

    解决方案

    Two options:

    • Create a list of values you wish to remove, adding to that list within the loop, then call originalList.removeAll(valuesToRemove) at the end
    • Use the remove() method on the iterator itself. Note that this means you can't use the enhanced for loop.

    As an example of the second option, removing any strings with a length greater than 5 from a list:

    List<String> list = new ArrayList<String>();
    ...
    for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); ) {
        String value = iterator.next();
        if (value.length() > 5) {
            iterator.remove();
        }
    }
    

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09-01 18:18