[英]ConcurrentModificationException when using iterator and iterator.remove()
private int checkLevel(String bigWord, Collection<String> dict, MinMax minMax)
{
/*value initialised to losing*/
int value = 0;
if (minMax == MinMax.MIN) value = 1;
else value = -1;
boolean go = true;
Iterator<String> iter = dict.iterator();
while(iter.hasNext())
{
String str = iter.next();
Collection<Integer> inds = naiveStringSearch(bigWord, str);
if(inds.isEmpty())
{
iter.remove();
}
for (Integer i : inds)
{
MinMax passin = minMax.MIN;
if (minMax == MinMax.MIN) passin = minMax.MAX;
int value2 = checkLevel(removeWord(bigWord, str, i), dict, passin);
if (value2 == -1 && minMax == minMax.MIN)
{
value = -1;
go = false;
}
if (value2 == 1 && minMax == minMax.MAX)
{
value = 1;
go = false;
}
}
if (go == false) break;
}
return value;
}
Error: 错误:
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:810)
at java.util.HashMap$KeyIterator.next(HashMap.java:845)
at aStringGame.Main.checkLevel(Main.java:67)
at aStringGame.Main.test(Main.java:117)
at aStringGame.Main.main(Main.java:137)
What's the problem here? 这有什么问题?
Something somewhere is modifying dict
. 某处某处正在修改
dict
。 I suspect it might be happening inside this call: 我怀疑它可能会在这个电话中发生:
int value2 = checkLevel(removeWord(bigWord, str, i), dict, passin);
^^^^
edit Basically, what happens is that the recursive call to checkLevel()
modifies dict
through another iterator. 编辑基本上,会发生的事情是对
checkLevel()
的递归调用通过另一个迭代器修改dict
。 This makes the outer iterator's fail-fast behaviour to kick in. 这使得外部迭代器的快速失败行为成为可能。
You can't modify a Collection while you're iterating over it with an Iterator. 在使用迭代器迭代它时,您无法修改集合。
Your attempt to call iter.remove() breaks this rule (your removeWord method might, too). 您尝试调用iter.remove()会破坏此规则(也可能是您的removeWord方法)。
You CAN modify a List while iterating IF you use a ListIterator to iterate. 如果你使用,你可以修改列表,而迭代的ListIterator迭代。
You can convert your Set to a List and use a List iterator: 您可以将Set转换为List并使用List迭代器:
List<String> tempList = new ArrayList<String>(dict);
ListIterator li = tempList.listIterator();
Another option is to keep track of the elements you want to remove while iterating. 另一种选择是在迭代时跟踪要删除的元素。
You could place them in a Set, for example. 例如,您可以将它们放在Set中。
You could then call dict.removeAll() after your loop. 然后,您可以在循环后调用dict.removeAll() 。
Example: 例:
Set<String> removeSet = new HashSet<String>();
for (String s : dict) {
if (shouldRemove(s)) {
removeSet.add(s);
}
}
dict.removeAll(removeSet);
When using a for each
loop you are not allowed to modify the Collection
you are iterating inside the loop. 当
for each
循环使用a时for each
不允许修改在循环内迭代的Collection
。 If you need to modify it, use a classic for
loop 如果需要修改它,请使用经典的
for
循环
This is a common occurance in all Collections classes. 这在所有Collections类中都很常见。 For instance the entry in TreeSet uses failfast method.
例如,TreeSet中的条目使用failfast方法。
The iterators returned by this class's iterator method are fail-fast: if the set is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will throw a ConcurrentModificationException.
这个类的迭代器方法返回的迭代器是快速失败的:如果在创建迭代器之后的任何时候修改了set,除了通过迭代器自己的remove方法之外,迭代器将抛出ConcurrentModificationException。 Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
因此,在并发修改的情况下,迭代器快速而干净地失败,而不是在未来的未确定时间冒着任意的,非确定性行为的风险。
http://docs.oracle.com/javase/6/docs/api/java/util/TreeSet.html http://docs.oracle.com/javase/6/docs/api/java/util/TreeSet.html
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