Java Linked List remove object method

Question

I want to remove the element if it is present in a linkedlist while iterating over an array of numbers

for(int num : numbers)
{
   if(l.contains(num))
   {
      l.remove(num);
   }
}

However, it is trying to remove element at index num, instead of looking for num in the linked list.

The javadoc has this method

remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present.

How to use it?

Thanks, it worked. So is it because if we use a primitive type, it takes it for index? So we have wrap it as object? — user2133404, Dec 16 '13 at 16:59
@ZouZou Use `l.remove(Integer.valueOf(num))`, not `new Integer(num)`. — AJMansfield, Dec 16 '13 at 17:01
@user2133404 `foreach` loops use an iterator to walk over the list, and altering the list while iterating over it invalidates the iterator. — Mike G, Dec 16 '13 at 17:04

score 5 · Answer 1 · answered Dec 16 '13 at 17:01

5

You can do this instead

for(Integer num : numbers)
    l.remove(num); // remove if present

This avoids the confusion with List.remove(int index) called if you pass it an int and List.remove(Object) called if you pass it an object like Integer and avoids scanning the list twice if the element is present.

answered Dec 16 '13 at 17:01

Peter Lawrey

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@AJMansfield and what's the problem? – Olimpiu POP Dec 16 '13 at 17:14
@user503413 actually now that I think some more, that isn't really a problem at all. – AJMansfield Dec 16 '13 at 17:18

score 1 · Answer 2 · edited Dec 16 '13 at 17:08

1

You should box it in an Integer like this:

l.remove(Integer.valueOf(num));

or iterate over Integer objects instead of ints.

edited Dec 16 '13 at 17:08

AJMansfield

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answered Dec 16 '13 at 17:01

Adam Arold

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score 1 · Answer 3 · answered Dec 16 '13 at 17:26

1

I would instead just do this:

l.removeAll(Arrays.asList(numbers));

answered Dec 16 '13 at 17:26

AJMansfield

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score 0 · Answer 4 · edited Dec 16 '13 at 17:07

0

You will need to call remove(Object): invocation of remove(num) is not matching with the function with signature remove(Object o) where the function parameter is of reference type. instead it matches with remove(int index).

Hence, invoking remove(Integer.valueOf(num)) will work as it will pass a reference type.

edited Dec 16 '13 at 17:07

AJMansfield

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answered Dec 16 '13 at 17:01

Sage

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Java Linked List remove object method

4 Answers4