Removing items from a list

Question

While looping through a list  I would like to remove an item of a list depending on a condition  See the code below   This gives me a ConcurrentModification exception   for  Object a   list        if  a getXXX   equalsIgnoreCase  AAA              logger info  this is AAA        should be removed from the list             list remove a             How can this be done

User · Answer

Besides all the excellent solutions offered here I would like to offer a different solution.

I'm not sure if you're free to add dependencies, but if you can, you could add the https://code.google.com/p/guava-libraries/ as a dependency. This library adds support for many basic functional operations to Java and can make working with collections a lot easier and more readable.

In the code I replaced the type of the List by T, since I don't know what your list is typed to.

This problem can with guava be solved like this:

List<T> filteredList = new Arraylist<>(filter(list, not(XXX_EQUAL_TO_AAA)));

And somewhere else you then define XXX_EQUAL_TO_AAA as:

public static final Predicate<T> XXX_EQUAL_TO_AAA = new Predicate<T>() {
    @Override
    public boolean apply(T input) {
        return input.getXXX().equalsIgnoreCase("AAA");
    }
}

However, this is probably overkill in your situation. It's just something that becomes increasingly powerful the more you work with collections.

Ohw, also, you need these static imports:

import static com.google.common.base.Predicates.not;
import static com.google.common.collect.Collections2.filter;

User · Answer

You need to use Iterator and call remove   on iterator instead of using for loop

User · Answer

for  Iterator lt String gt  iter   list listIterator    iter hasNext            String a   iter next        if                 iter remove              Making an additional assumption that the list is of strings  As already answered  an list iterator   is needed  The listIterator can do a bit of navigation too

User · Answer

You can t and shouldn t modify a list while iterating over it  You can solve this by temporarely saving the objects to remove   List lt Object gt  toRemove   new ArrayList lt Object gt     for Object a  list       if a getXXX   equalsIgnoreCase  AAA             toRemove add a           list removeAll toRemove

User · Answer

You cannot do it because you are already  looping on it   Inorder to avoid this situation use Iterator which guarentees you to remove the element from list safely      List lt Object gt  objs  Iterator lt Object gt  i   objs iterator    while  i hasNext         Object o   i next        some condition     i remove

User · Answer

first find out the removed ones  List removedList   new ArrayList    for Object a  list       if a getXXX   equalsIgnoreCase  AAA             logger info  this is AAA        should be removed from the list             removedList add a             list removeAll removedList

[java] Removing items from a list

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