Java - Memento pattern and Undo

Question

I am implementing an undo/redo function which requires me to use memento pattern.

The flow of the partial program : \"...the program then store the previous Vector u

Answer 1

The memento pattern is used to save the state of an object without knowing it's internal data structures.

I try to explain it with an Iterator example

public class MementoListIterator<E> implements Iterator<E> {

    public static class Memento {

        private int savedIndex;

        private Memento(MementoListIterator<?> mementoListIterator) {
            this.savedIndex = mementoListIterator.index;
        }

    }

    private List<E> elements;

    private int index = 0;

    public MementoListIterator(List<E> elements) {
        this.elements = elements;
    }

    public Memento save() {
        return new Memento(this);

    }

    public void restore(Memento memento) {
        this.index = memento.savedIndex;
    }

    @Override
    public boolean hasNext() {
        return this.index < elements.size();
    }

    @Override
    public E next() {
        return elements.get(index++);
    }

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

A client can now save any state of the iterator without knowing how the iterator internally manages it's state.

public class Main {

    public static void main(String[] args) {
        List<String> list = Arrays.asList("A", "B", "C", "D", "E");
        MementoListIterator<String> mementoListIterator = new MementoListIterator<String>(
                list);

        Memento initialState = mementoListIterator.save();

        while (mementoListIterator.hasNext()) {
            String string = mementoListIterator.next();
            System.out.println(string);
        }
                    // Normally we can not re-use the iterator, but
                    // fortuanatly we saved the initial state.

        // restore the initial state and we can use the Iterator again
        mementoListIterator.restore(initialState);

        while (mementoListIterator.hasNext()) {
            String string = mementoListIterator.next();
            System.out.println(string);
        }
    }
}