带迭代器的java.util.ConcurrentModificationException [英] java.util.ConcurrentModificationException with iterator

问题描述

我知道如果试图通过简单的循环从集合中删除循环，我将得到这个异常： java.util.ConcurrentModificationException 。但我正在使用Iterator，它仍然会产生这个异常。知道为什么以及如何解决它？

I know if would be trying to remove from collection looping through it with the simple loop I will be getting this exception: java.util.ConcurrentModificationException. But I am using Iterator and it still generates me this exception. Any idea why and how to solve it?

HashSet<TableRecord> tableRecords = new HashSet<>();

...

    for (Iterator<TableRecord> iterator = tableRecords.iterator(); iterator.hasNext(); ) {
        TableRecord record = iterator.next();
        if (record.getDependency() == null) {
            for (Iterator<TableRecord> dependencyIt = tableRecords.iterator(); dependencyIt.hasNext(); ) {
                TableRecord dependency = dependencyIt.next(); //Here is the line which throws this exception
                if (dependency.getDependency() != null && dependency.getDependency().getId().equals(record.getId())) {
                    iterator.remove();
                }
            }
        }
    }

推荐答案

您必须使用 iterator.remove（）而不是 tableRecords.remove（）

只有在迭代器中使用remove方法时，才能删除迭代列表中的项目。

You can remove items on a list on which you iterate only if you use the remove method from the iterator.

编辑：

创建迭代器时，它开始计算对集合应用的修改。如果迭代器检测到某些修改没有使用它的方法（或在同一个集合上使用另一个迭代器），它就不能再保证它不会在同一个元素上传递两次或跳过一个，所以它抛出了这个异常

When you create an iterator, it starts to count the modifications that were applied on the collection. If the iterator detects that some modifications were made without using its method (or using another iterator on the same collection), it cannot guarantee anymore that it will not pass twice on the same element or skip one, so it throws this exception

这意味着您需要更改代码，以便只通过iterator.remove删除项目（并且只使用一个迭代器）

It means that you need to change your code so that you only remove items via iterator.remove (and with only one iterator)

OR

制作一个要删除的项目列表，然后在完成迭代后删除它们。

make a list of items to remove then remove them after you finished iterating.

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