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UnsupportedOperationException while removing element from List

Posted on 2008-06-10
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Last Modified: 2008-06-10
Hello

 i have a List<File> queryPool;

 in findImage() method, I loop thru the queryPool and find one image called queryImage of type File, which i return to main function

 and while trying to remove this from the queryPool -

queryPool.remove(queryImage);

it throws the java.lang.UnsupportedOperationException .. i tried using Iterator over the queryPool, still error

any comments?
protected File findImage() {
 // some calculations
 
 for(File f : queryPool) {
   // calculations
 
   if(closeValues.get(f) < temp2) {
	queryImage = f;
   }
 }
 
return queryImage;
}

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Question by:max_dub
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8 Comments
 
LVL 86

Accepted Solution

by:
CEHJ earned 1000 total points
ID: 21751430
If you want to remove it while iterating, you should


a. clone the File to return to the caller
b. Use Iterator explicitly and call remove on it
0
 
LVL 17

Expert Comment

by:contactkarthi
ID: 21751448
once you have created an iterator for a collection you should explicitly use the add and remove methods from the iterator. if you try to add or remove from the collection directly you will get the exception.
0
 

Author Comment

by:max_dub
ID: 21751479
"explicitly use the add and remove methods" - can u explain this bit
0
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LVL 10

Assisted Solution

by:mukundha_expert
mukundha_expert earned 1000 total points
ID: 21751539
check your list implementation,
if you are trying to get the list using Arrays.asList(), then the returned list do not support
the remove,

since it is java.util.Arrays$ArrayList and not java.util.ArrayList
chekc the class with list.getClass()
0
 
LVL 10

Expert Comment

by:mukundha_expert
ID: 21751559
if you use an iterator and try to remove the object from the list, it should throw a ConcurrentModificationException and not UnSuportedOperationExcepotion,

UnSupported..Exception is thrown by the remove() method in the AbstractList(), if the implementation of this class do no impleemnt remove() then u will get that exception

0
 
LVL 86

Expert Comment

by:CEHJ
ID: 21751628
This is the sort of thing you need to do
        List<File> fileList = new ArrayList(Arrays.asList(new File(".").listFiles()));
        Iterator<File> i = fileList.iterator();
        String copied = null;
        while (i.hasNext()) {
            File f = i.next();
            if (f.getName().equals("b")) {
                copied = f.getName();
                i.remove();
            }
        }
        System.out.println(fileList);
        System.out.println(copied);

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0
 

Author Comment

by:max_dub
ID: 21751748
thanks guys..

i was missing the remove function from the List implementation from an external jar i was using.. i added the remove function there n it works

cheers
0
 

Author Comment

by:max_dub
ID: 21751756
ah, sorry i wanted the CEHJ answer to be assisted solution, but it turned out other way around .. always .. thanks mukundha_expert for ur solution
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