cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections IteratorChain.java

[mo...@apache.org]

morgand     02/04/08 16:38:48

  Added:       collections/src/java/org/apache/commons/collections
                        IteratorChain.java
  Log:
  An IteratorChain is a sequence of Iterators called until all Iterators are
  exhausted
  
  Revision  Changes    Path
  1.1                  jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorChain.java
  
  Index: IteratorChain.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorChain.java,v 1.1 2002/04/08 23:38:48 morgand Exp $
   * $Revision: 1.1 $
   * $Date: 2002/04/08 23:38:48 $
   *
   * ====================================================================
   *
   * The Apache Software License, Version 1.1
   *
   * Copyright (c) 1999-2001 The Apache Software Foundation.  All rights
   * reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. The end-user documentation included with the redistribution, if
   *    any, must include the following acknowlegement:
   *       "This product includes software developed by the
   *        Apache Software Foundation (http://www.apache.org/)."
   *    Alternately, this acknowlegement may appear in the software itself,
   *    if and wherever such third-party acknowlegements normally appear.
   *
   * 4. The names "The Jakarta Project", "Commons", and "Apache Software
   *    Foundation" must not be used to endorse or promote products derived
   *    from this software without prior written permission. For written
   *    permission, please contact apache@apache.org.
   *
   * 5. Products derived from this software may not be called "Apache"
   *    nor may "Apache" appear in their names without prior written
   *    permission of the Apache Group.
   *
   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  package org.apache.commons.collections;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.NoSuchElementException;
  
  /**
   * <p>An IteratorChain is an Iterator that wraps one or
   * more Iterators in sequence.  When any method from the
   * Iterator interface is called, the IteratorChain will
   * call the same method on the first Iterator in the chain
   * until it is exhausted until the first Iterator is exhausted.
   * At that point, the IteratorChain will move to the next
   * Iterator in the IteratorChain.  The IteratorChain will
   * continue in this pattern until all Iterators in the
   * IteratorChain are exhausted.</p>
   * 
   * <p>Under many circumstances, linking Iterators together
   * in this manner is more efficient (and convenient)
   * than reading out the contents of each Iterator into a
   * List and creating a new Iterator.</p>
   * 
   * <p>IteratorChain is Serializable, but there is no
   * guarantee that the underlying Iterators are
   * Serializable.</p>
   * 
   * <p>Calling a method that adds new Iterator<i>after
   * a method in the Iterator interface
   * has been called</i> will result in an
   * UnsupportedOperationException.  However, <i>take care</i>
   * to not alter the underlying List of Iterators.</p>
   * 
   * @author Morgan Delagrange
   */
  public class IteratorChain implements Iterator {
  
      protected List iteratorChain = null;
      protected int currentIteratorIndex = 0;
      protected Iterator currentIterator = null;
      // the "last used" Iterator is the Iterator upon which
      // next() or hasNext() was most recently called
      // used for the remove() operation only
      protected Iterator lastUsedIterator = null;
  
      // ComparatorChain is "locked" after the first time
      // compare(Object,Object) is called
      protected boolean isLocked = false;
  
      /**
       * Construct an IteratorChain with no Iterators.
       * You must add at least Iterator before calling
       * any method from the Iterator interface, or an 
       * UnsupportedOperationException is thrown
       */
      public IteratorChain() {
          this(new ArrayList());
      }
  
      /**
       * Construct an IteratorChain with a single Iterator.
       * 
       * @param iterator first Iterator in the IteratorChain
       */
      public IteratorChain(Iterator iterator) {
          iteratorChain = new ArrayList();
          iteratorChain.add(iterator);
      }
  
      /**
       * Construct an IteratorChain from the Iterators in the
       * List.
       * 
       * @param list   List of Iterators
       */
      public IteratorChain(List list) {
          iteratorChain = list;
      }
  
      /**
       * Add an Iterator to the end of the chain 
       * 
       * @param iterator Iterator to add
       */
      public void addIterator(Iterator iterator) {
          checkLocked();
  
          iteratorChain.add(iterator);
      }
  
      /**
       * Replace the Iterator at the given index     
       * 
       * @param index      index of the Iterator to replace
       * @param iterator   Iterator to place at the given index
       * @exception IndexOutOfBoundsException
       *                   if index < 0 or index > size()
       */
      public void setIterator(int index, Iterator iterator) 
      throws IndexOutOfBoundsException {
          checkLocked();
  
          iteratorChain.set(index,iterator);
      }
  
      /**
       * Number of Iterators in the current IteratorChain.
       * 
       * @return Iterator count
       */
      public int size() {
          return iteratorChain.size();
      }
  
      /**
       * Determine if modifications can still be made to the
       * IteratorChain.  IteratorChains cannot be modified
       * once they have executed a method from the Iterator
       * interface.
       * 
       * @return true = IteratorChain cannot be modified; false = 
       *         IteratorChain can still be modified.
       */
      public boolean isLocked() {
          return isLocked;
      }
  
      // throw an exception if the IteratorChain is locked
      private void checkLocked() {
          if (isLocked == true) {
              throw new UnsupportedOperationException("IteratorChain cannot be changed after the first use of a method from the Iterator interface");
          }
      }
  
      private void checkChainIntegrity() {
          if (iteratorChain.size() == 0) {
              throw new UnsupportedOperationException("IteratorChains must contain at least one Iterator");
          }
      }
  
      // you MUST call this method whenever you call a method in the Iterator interface, because
      // this method also assigns the initial value of the currentIterator variable
      private void lockChain() {
          if (isLocked == false) {
              checkChainIntegrity();
              isLocked = true;
          }
      }
  
      // call this before any Iterator method to make sure that the current Iterator
      // is not exhausted
      protected void updateCurrentIterator() {
          if (currentIterator == null) {
              currentIterator = (Iterator) iteratorChain.get(0);
              // set last used iterator here, in case the user calls remove
              // before calling hasNext() or next() (although they shouldn't)
              lastUsedIterator = currentIterator;
              return;
          }
  
          if (currentIteratorIndex == (iteratorChain.size() - 1)) {
              return;
          }
  
          while (currentIterator.hasNext() == false) {
              ++currentIteratorIndex;
              currentIterator = (Iterator) iteratorChain.get(currentIteratorIndex);
  
              if (currentIteratorIndex == (iteratorChain.size() - 1)) {
                  return;
              }
          }
      }
  
      /**
       * Return true if any Iterator in the IteratorChain has a remaining
       * element.
       * 
       * @return true if elements remain
       * @exception UnsupportedOperationException
       *                   if the IteratorChain does not contain at least one
       *                   Iterator
       */
      public boolean hasNext() throws UnsupportedOperationException {
          lockChain();
          updateCurrentIterator();
          lastUsedIterator = currentIterator;
  
          return currentIterator.hasNext();
      }
  
      /**
       * Returns the next Object of the current Iterator
       * 
       * @return Object from the current Iterator
       * @exception NoSuchElementException
       *                   if all the Iterators are exhausted
       * @exception UnsupportedOperationException
       *                   if the IteratorChain does not contain at least one
       *                   Iterator
       */
      public Object next() throws NoSuchElementException, UnsupportedOperationException {
          lockChain();
          updateCurrentIterator();
          lastUsedIterator = currentIterator;
  
          return currentIterator.next();
      }
  
      /**
       * Removes from the underlying collection the last element 
       * returned by the Iterator.  As with next() and hasNext(),
       * this method calls remove() on the underlying Iterator.
       * Therefore, this method may throw an 
       * UnsupportedOperationException if the underlying
       * Iterator does not support this method. 
       * 
       * @exception UnsupportedOperationException
       *                   if the remove operator is not supported by the underlying
       *                   Iterator or if there are no Iterators in the IteratorChain
       * @exception IllegalStateException
       *                   if the next method has not yet been called, or the
       *                   remove method has already been called after the last
       *                   call to the next method.
       */
      public void remove() throws UnsupportedOperationException, IllegalStateException  {
          lockChain();
          updateCurrentIterator();
  
          lastUsedIterator.remove();
      }
  
  
  }
  
  
  

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