remove one Collection elements from other

Question

Hi i have two Collection of SomeType a1,a2 and want to remove all the elements of a2 from a1.

Please suggestion which type of Collection i need to use :

1. ArrayList
2. LinkList
3. some other ?.

Is there any library for this ?

Answer 1

Thanks to all. After reading your response i created a Filter class like this :

public class Filter {

    public <T> Set<T> filter(Set<T> all, Set<T> blocked) {
        for (T t : all) {
            if(blocked.contains(t)) {
                all.remove(t);
            }
        }
        return all;
    }
}

Answer 2

使用收集方法Collection.removeAll(Collection<?> c);

Answer 3

Well, you can use a1.removeAll(a2) , but the removal would be more efficient if your Collections are HashSet (since the search for an element in a HashSet takes O(1) , while in List s it takes O(n) ). Whether you can use HashSet depends on whether a1 and a2 can contain duplicate elements.

Answer 4

To remove from a collection you need to have objects(in your case SomeType) that override equals and hashCode . Then you don't need a library, just use the removeAll method

Collection<SomeType> a1 = new ArrayList<SomeType>();
Collection<SomeType> a2 = new ArrayList<SomeType>();
a1.removeAll(a2);