Implementing an iterator for an unmodifiable list

Question

I'm implementing an unmodifiable list based on AbstractSequentialList. Now, according to Oracle's documentation:

For an unmodifiable list, the programmer need only implement the list iterator's hasNext, next, hasPrevious, previous and index methods.

The problem is that it seems I must provide an implementation for remove, set and add methods, although these are not needed at all due the unmodifiable nature of the list, otherwise the compiler complains because these methods are not implemented.

So, am I doing something wrong or is this the real way to go? am I supposed to implement such methods and throw some kind of exception within them or so?

Thanks a lot in advance,

Answer 1

Just throw an UnsupportedOperationException on the methods you do not need to implement. As specified by the Iterator/ListIterator interface documentation https://docs.oracle.com/javase/7/docs/api/java/util/ListIterator.html#remove()

Throws: UnsupportedOperationException - if the remove operation is not supported by this list iterator

e.g.

@Override
public void remove() {
    throw new UnsupportedOperationException("Not supported yet.");
}

Answer 2

http://docs.oracle.com/javase/6/docs/api/java/lang/UnsupportedOperationException.html

Thrown to indicate that the requested operation is not supported.

e.g.

@Override
public void remove() {
    throw new UnsupportedOperationException("Cannot remove from unmodifiableList");
}