[英]Cannot figure out why it throws ConcurrentModificationException
[英]I cannot figure out why I have this error: ConcurrentModificationException
我正在编写一个解决Mastermind游戏的程序。 该程序的要旨是列出所有可能的解决方案,并在每一次都不正确的猜测之后,从列表中删除至少不会给出该解决方案的任何内容。 使用此方法来比较两个字符串(guess和strFromArray)以查看它们是否获得相同的值。 但是,我遇到了一个错误,我不知道为什么。 任何帮助,将不胜感激。
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)
at Game.shortenTheList(Game.java:88)
at Game.guess(Game.java:76)
at Game.play(Game.java:40)
at Game.main(Game.java:23)
/*
* Compares the two strings. If they would get the same output, return false. If they would get a different output, return true.
*/
public boolean compare(String guess, String strFromArray, int black, int white)
{
int white2 = 0;
int black2 = 0;
char[] arr1 = guess.toCharArray();
char[] arr2 = strFromArray.toCharArray();
for(int i=0; i<guess.length(); i++)
{
if(arr1[i] == arr2[i])
{
black2 ++;
arr1[i] = '$';
arr2[i] = '%';
}
}
for(int i=0; i<guess.length(); i++)
{
for(int j=0; j<strFromArray.length(); j++)
{
if(arr1[i] == arr2[j])
{
white2++;
arr1[i] = '!';
arr2[j] = '@';
}
}
}
if(black == black2 && white == white2)
return false;
else
return true;
}
/*
* Shortens the list of possible solutions by eliminating everything that wouldn't get at least the given output.
*/
public void shortenTheList(String guess, int black1, int white1)
{
for (String str : possibleSolutions)
{
if(compare(guess, str, black1, white1))
{
possibleSolutions.remove(str);
}
}
}
一旦打开了Iterator
(在使用for(String str: possibleSolutions)
PossibleSolutions时隐式地进行for(String str: possibleSolutions)
,对基础集合( possibleSolutions
)的任何修改(除非通过在Iterator
上调用remove
)都将导致ConcurrentModificationException
;这在集合类中非常清楚地记录了下来。 。
如果您需要从集合中删除项目,请使用显式的Iterator
:
Iterator<String> it = possibleSolutions.iterator();
while(it.hasNext()) {
if(compare(guess, it.next(), black1, white1))
it.remove();
}
正如@allprog指出的那样,当您遇到如此明显的“过滤”问题时,功能性方法会更好。 在选择Java 8之前,使用Guava的Iterables#filter
或Iterables#removeIf
可能是一个不错的选择。 您只需包装您的compare
方法并将其传递。
/*
* Shortens the list of possible solutions by eliminating everything that wouldn't get at least the given output.
*/
public void shortenTheList(String guess, int black1, int white1)
{
for (String str : possibleSolutions)
{
if(compare(guess, str, black1, white1))
{
possibleSolutions.remove(str);
}
}
}
有你的问题。
而是使用:
/*
* Shortens the list of possible solutions by eliminating everything that wouldn't get at least the given output.
*/
public void shortenTheList(String guess, int black1, int white1)
{
Iterator<String> it = possibleSolutions.iterator();
while(it.hasNext())
{
String str = it.next();
if(compare(guess, str, black1, white1))
{
it.remove();
}
}
}
这是从当前正在迭代的集合中删除对象的唯一干净方法。 另一种不太优雅的方法是创建一个单独的String
列表以删除并对其进行迭代。
当您使用foreach循环遍历列表时,您将无法修改possibleSolutions列表。
将您的代码更改为如下所示:
public void shortenTheList(String guess, int black1, int white1)
{
for(Iterator<String> it = possibleSolutions.iterator(); it.hasNext()){
String str = it.next();
if(compare(guess, str, black1, white1)){
it.remove();
}
}
}
就像chrylis所说的那样,如果不使用Iterator,就无法从集合中删除元素。
例:
public void shortenTheList(String guess, int black1, int white1)
{
for (String str : possibleSolutions)
{
if(compare(guess, str, black1, white1))
{
possibleSolutions.remove(str);
}
}
}
应该:
public void shortenTheList(String guess, int black1, int white1)
{
Iterator i = possibleSolutions.Iterator();
while(i.hasNext())
{
String str = (String) i.next();
if(compare(guess, str, black1, white1))
{
i.remove();
}
}
}
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