从具有不连续索引的列表创建子列表

Question

In Java, I would like to use the clear() method on a list so that the items cleared from the sublist are also removed from the original list. Is there a way to create a sublist where the indices are non continuous, so that I can still use the clear() method to remove the items from the original list?

Answer 1

Nope. Calling clear() on the sublist removes the elements from the original list, but also updates indices.

If you want to retain the indices, instead of using .clear() you can use .set(i, null) - this will retain "empty slots" in the list. You'll just need to be careful when iterating. Another thing you can do is use a Map<Integer, Foo> where Integer is your index. That way you will be in charge of managing the indices.

Update: if you want to remove particular elements, rather than a sublist, simply call .remove(index)

Answer 2

None of the default List implementations support this behavior. You could override ArrayList and support a clear() , remove() , etc.. that turns around and calls remove() on the parent list.

Something like the following example code. But to keep it properly in sync with the parent is going to take a lot of work . If you can limit the number of calls that you need to support then it would be a lot easier of course.

public class SubArrayList<T> extends ArrayList<T> {
    public SubArrayList(List<T> parentList, int start, int end) {
        ...;
    }

    @Override
    public T remove(int index) {
        T removed = super.remove(index);
        // should not remove by position because position in parent might change
        parentList.remove(removed);
        return removed;
    }

    @Override
    public T remove(Object obj) {
        if (super.remove(obj)) {
            parentList.remove(obj);
        }
    }
}