Iterator class for values contained in an array range. : Iterator « Collections « Java Tutorial

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/*
Copyright (c) 2000-2005, Dennis M. Sosnoski.
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*/


import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Iterator class for values contained in an array range. This type of iterator
 * can be used for any contiguous range of items in an object array.
 *
 * @author Dennis M. Sosnoski
 * @version 1.1
 */
public class ArrayRangeIterator implements Iterator
{
  /** Empty iterator used whenever possible. */
  public static final ArrayRangeIterator EMPTY_ITERATOR =
    new ArrayRangeIterator(null, 0, 0);

  /** Array supplying values for iteration. */
  protected Object[] m_array;

  /** Offset of next iteration value. */
  protected int m_offset;

  /** Ending offset for values. */
  protected int m_limit;

  /**
   * Internal constructor.
   *
   * @param array array containing values to be iterated
   * @param start starting offset in array
   * @param limit offset past end of values
   */
  private ArrayRangeIterator(Object[] array, int start, int limit) {
    m_array = array;
    m_offset = start;
    m_limit = limit;
  }

  /**
   * Check for iteration element available.
   *
   * @return <code>true</code> if element available, <code>false</code> if
   * not
   */
  public boolean hasNext() {
    return m_offset < m_limit;
  }

  /**
   * Get next iteration element.
   *
   * @return next iteration element
   * @exception NoSuchElementException if past end of iteration
   */
  public Object next() {
    if (m_offset < m_limit) {
      return m_array[m_offset++];
    } else {
      throw new NoSuchElementException();
    }
  }

  /**
   * Remove element from iteration. This optional operation is not supported
   * and always throws an exception.
   *
   * @exception UnsupportedOperationException for unsupported operation
   */
  public void remove() {
    throw new UnsupportedOperationException();
  }

  /**
   * Build iterator.
   *
   * @param array array containing values to be iterated (may be
   * <code>null</code>)
   * @param start starting offset in array
   * @param limit offset past end of values
   * @return constructed iterator
   */
  public static Iterator buildIterator(Object[] array, int start, int limit) {
    if (array == null || start >= limit) {
      return EMPTY_ITERATOR;
    } else {
      return new ArrayRangeIterator(array, start, limit);
    }
  }
}