package ca.uhn.hl7v2.testpanel.util;
   
   import java.util.Iterator;
   
   public class PushBackIterator<E> implements Iterator<E> {
   	private E myPreviousValue = null;
   	private E mySavedValue = null;
   	private final Iterator<E> myWrappedIterator;
   	
  	/**
  	 * Constructor
  	 */
  	public PushBackIterator(Iterator<E> theIteratorToWrap) {
  		this.myWrappedIterator = theIteratorToWrap;
  	}
  
  	/**
  	 * {@inheritDoc}
  	 */
  	public boolean hasNext() {
  		return mySavedValue != null || myWrappedIterator.hasNext();
  	}
  
  
  	/**
  	 * {@inheritDoc}
  	 */
  	public E next() {
  		if (mySavedValue != null) {
  			try {
  				return myPreviousValue = mySavedValue;
  			} finally {
  				mySavedValue = null;
  			}
  		}
  		return myPreviousValue = myWrappedIterator.next();
  	}
  
  
  	public E previous() {
  		return myPreviousValue;
  	}
  
  
  	public void pushBack() {
  		mySavedValue = myPreviousValue;
  	}
  
  
  	/**
  	 * {@inheritDoc}
  	 */
  	public void remove() {
  		if (mySavedValue != null) {
  			throw new IllegalStateException("Cannot remove when next element has been pushed back");
  		}
  		myWrappedIterator.remove();
  	}
  }