Removing entries from a list?

Question

Take a situation where you have, let's say, an ArrayList that supports a remove function -- it deletes the entry and shifts everything to the right of it left one.

If I want to remove things from the list under a certain condition, I might do this:

for (int i = 0; i < list.size(); i++) {
  if (condition) {
    list.remove(i);
    i--;
  }
}

but this is ugly and feels hackish. You could do the same with an Iterator, but you shouldn't be altering lists while using iterators.

So what's the non-ugly solution?

possible duplicate of [Deleting objects from an ArrayList in Java](http://stackoverflow.com/questions/1310532/deleting-objects-from-an-arraylist-in-java) — Brian Roach, Nov 03 '11 at 04:05

AusCBloke · Answer 1 · 2011-11-03T04:20:02.367

Iterators can in fact be used for that purpose, and is what the Oracle documentation recommends.

This is code provided by the above link under Traversing Collections - Iterators:

static void filter(Collection<?> c) {
    for (Iterator<?> it = c.iterator(); it.hasNext(); )
        if (!cond(it.next()))
            it.remove();
}

Most importantly, above that example they state:

Note that Iterator.remove is the only safe way to modify a collection during iteration; the behavior is unspecified if the underlying collection is modified in any other way while the iteration is in progress.

score 1 · Answer 2 · answered Nov 03 '11 at 04:03

1

I just use a loop, but decrement the counter instead

for(int i=list.size()-1; i>=0; --i) {
  if(condition) {
     list.remove(i);
  }
}

answered Nov 03 '11 at 04:03

aleph_null

5,766
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No, what that means is that you can't safely modify the collection while traversing it **with an iterator**. I'm not using an iterator, I'm using a loop. – aleph_null Nov 03 '11 at 04:14
Oh woops you're not using an iterator, my bad. – AusCBloke Nov 03 '11 at 04:18

score 0 · Answer 3 · answered Jan 23 '14 at 17:16

Guava provides some functional flavour to Java. In your case it would be:

 FluentIterable.from(your_iterable).filter(new Predicate<Type_contained_in_your_iterable>()                    {
            @Override
            public boolean apply(@Nullable Type_contained_in_your_iterable input) {
                return {condition};
            }
        });

Note that your predicate will only return the elements from your iterable satisfying your condition. Much clearer like this. Isn't it.

score 0 · Answer 4 · answered Nov 03 '11 at 04:05

Try this

Iterator itr = list.iterator(); 
while(itr.hasNext()) {
if(condition)
    itr.remove();
}

Hope so this shud work.. try else ll suggest another one

I have another one for you which checks for condition too....

int count=0;
Iterator itr = list.iterator(); 
while(itr.next()) {
count++;
if(condition=count)
    itr.remove();
}

Removing entries from a list?

4 Answers4