AbstractIterator.java

public abstract class AbstractIterator<T> implements Iterator<T>
{
  private boolean hasMoreData = true, nextComputed;
  private T data;

  @Override
  public final boolean hasNext()
  {
    if (hasMoreData && !nextComputed)
    {
      data = computeNext();
      nextComputed = true;
    }
    return hasMoreData;
  }

  @Override
  public final T next()
  {
    if (!hasNext())
      throw new NoSuchElementException();
    nextComputed = false;
    return data;
  }

  protected abstract T computeNext();

  protected final T endOfData()
  {
    hasMoreData = false;
    return null;
  }
}