import java.util.LinkedList;
import java.util.ListIterator;

public class Main {
		public static void main(String[] args) {
			final LinkedList<String> list = new LinkedList<String> ();
			
			list.add ("1"); list.add ("2"); list.add ("3"); list.add ("4");
			
			final MyIterator<String> it = new MyIterator (list.listIterator());
			
			System.out.println(it.next());
			System.out.println(it.next ());
			System.out.println(it.next ());
			System.out.println(it.previous ());
			System.out.println(it.previous ());
			System.out.println(it.next ());
		}
		
		public static class MyIterator<T> {
	
			private final ListIterator<T> listIterator;
	
			private boolean nextWasCalled = false;
			private boolean previousWasCalled = false;
			
			public MyIterator(ListIterator<T> listIterator) {
				this.listIterator = listIterator;
			}
	
			public T next() {
				nextWasCalled = true;
				if (previousWasCalled) {
					previousWasCalled = false;
					listIterator.next ();
				}
				return listIterator.next ();
			}
	
			public T previous() {
				if (nextWasCalled) {
					listIterator.previous();
					nextWasCalled = false;
				}
				previousWasCalled = true;
				return listIterator.previous();
			}
	
		}	
	}