CODEWITHSUNDEEP
javacollectionsremoveall
mengying.ye
mengying.ye

Reputation: 877

Why need to judge the element if or not exsit in a collection in removeAll(Collection c)？

could you help me understand this snippet? I don't understand why this function have to check the collection contains the element before remove it. Since the iterator is from the collection, all element returned by iterator is definitely in collection.So I think it's a waste of time. Thank you a lot

   public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    boolean modified = false;
    Iterator<?> it = iterator();
    while (it.hasNext()) {
        if (c.contains(it.next())) {//I don't understand
            it.remove();
            modified = true;
        }
    }
    return modified;
}

Upvotes: 0

Views: 44

Answers (2)

Eran
Eran

Reputation: 393811

This looks like an implementation of Set's removeAll.

The iterator is not iterating on the Collection passed to the method. It is iterating on the Set on which the method was called.

set1.removeAll(collection2);

You are iterating over the elements of set1 and check for each one of them whether it belongs to collection2 before removing it from the Set.

Upvotes: 3

Elliott Frisch
Elliott Frisch

Reputation: 201437

That snippet is from a class that implements Collection. The method only removes items from the local class instance (through the local iterator()) when the Collection c also contains an item that is equals.

Upvotes: 0

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