Collections removeAll method

Question

I would like to know if something like below is possible,

list.removeAll(namesToRemove)

I hope the context is understandable.

The

Answer 1

You can do something like this using Google Collections Collections2.filter():

final List<String> namesToKeep = getNamesToFilter();
List<MyObject> filtered = Collections2.filter(originalList, new Predicate<MyObject>() {
  @Override
  public boolean apply(MyObject o) {
    return namesToKeep.contains(o.getName());
  }
});

Answer 2

Java 8:

list.removeIf(obj -> namesToRemove.contains(obj.getName()));

Java 7 and older:

Iterator<MyObject> iter = list.iterator();
while (iter.hasNext())
    if (namesToRemove.contains(iter.next().getName()))
        iter.remove();

---

Note that both alternatives have quadratic complexity. You can make it linear by doing

Set<String> namesToRemoveSet = new HashSet<>(namesToRemove);

before the snippets, and use namesToRemoveSet instead of namesToRemove.

Answer 3

You don't want to override anything in the Object class. You need to use either a filter utility or a collection that uses your own semantics instead of equals, maybe a ForwardingCollection wrapped around your own implementation of equivalence.

All this can be achieved with google guava without breaking any standards

Answer 4

Collection<MyObject> list = Collections2.filter(list, mo -> !namesToRemove.contains(mo.getName()));

Answer 5

Another approach: Subclass ArrayList and implement a custom method like:

public class MyArrayList<E> extends ArrayList<E> {

   // all needed constructors

   public void removeAllWithNames(Collection<String> names) {
     // following code is based on aioobe's answer
     Iterator<E> iter = iterator();
       while (iter.hasNext())
         if (names.contains(iter.next().toString()))
           iter.remove();
   }
}

EDIT changed the code - the comment was good, now the custom list is a 'List' again, but now we use the toString() method (for simplicity) for filtering. (using a getName() method is possible but requires more lines of code)