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

[sc...@apache.org]

scolebourne    2002/11/21 15:09:01

  Added:       collections/src/java/org/apache/commons/collections/iterators
                        LoopingIterator.java
  Log:
  Add LoopingIterator, from Jonathan Carlson
  
  Revision  Changes    Path
  1.1                  jakarta-commons/collections/src/java/org/apache/commons/collections/iterators/LoopingIterator.java
  
  Index: LoopingIterator.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-commons/collections/src/java/org/apache/commons/collections/iterators/LoopingIterator.java,v 1.1 2002/11/21 23:09:01 scolebourne Exp $
   * $Revision: 1.1 $
   * $Date: 2002/11/21 23:09:01 $
   *
   * ====================================================================
   *
   * 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.iterators;
  
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  /**
   * <code>LoopingIterator</code> provides an Iterator that restarts when it
   * reaches the end.
   * <p>
   * The iterator will loop continuously around the provided elements, unless 
   * there are no elements in the collection to begin with, or all the elements
   * are removed using the {@link remove} method.
   * <p>
   * Concurrent modifications are not directly supported, and for most collection
   * implementations will throw a ConcurrentModificationException. 
   *
   * @since 2.2
   * @author <a href="mailto:joncrlsn@users.sf.net">Jonathan Carlson</a>
   * @author Stephen Colebourne
   * @version $Revision: 1.1 $
   */
  public class LoopingIterator implements Iterator {
      /** The collection to base the iterator on */
      private Collection collection;
      /** The current iterator */
      private Iterator iterator;
  
      /**
       * Constructor that wraps a collection.
       * <p>
       * There is no way to reset an Iterator instance without recreating it from
       * the original source, so the Collection must be passed in.
       * 
       * @param coll  the collection to wrap
       * @throws NullPointerException if the collection is null
       */
      public LoopingIterator(Collection coll) {
          if (coll == null) {
              throw new NullPointerException("The collection must not be null");
          }
          collection = coll;
          reset();
      }
  
      /** 
       * Has the iterator any more elements.
       * <p>
       * Returns false only if the collection originally had zero elements, or
       * all the elements have been removed using {@link #remove}.
       * 
       * @return <code>true</code> if there are more elements
       */
      public boolean hasNext() {
          return (collection.size() > 0);
      }
  
      /**
       * Returns the next object in the collection.
       * <p>
       * If at the end of the collection, return the first element.
       * 
       * @throws NoSuchElementException if there are no elements
       *         at all.  Use {@link #hasNext} to avoid this error.
       */
      public Object next() {
          if (collection.size() == 0) {
              throw new NoSuchElementException("There are no elements for this iterator to loop on");
          }
          if (iterator.hasNext() == false) {
              reset();
          }
          return iterator.next();
      }
  
      /**
       * Removes the previously retrieved item from the underlying collection.
       * <p>
       * This feature is only supported if the underlying collection's 
       * {@link #iterator} method returns an implementation that supports it.
       * <p>
       * This method can only be called after at least one {@link #next} method call.
       * After a removal, the remove method may not be called again until another
       * next has been performed. If the {@link #reset} is called, then remove may
       * not be called until {@link #next} is called again.
       */
      public void remove() {
          iterator.remove();
      }
  
      /**
       * Resets the iterator back to the start of the collection.
       */
      public void reset() {
          iterator = collection.iterator();
      }
  
      /**
       * Gets the size of the collection underlying the iterator.
       * 
       * @return the current collection size
       */
      public int size() {
          return collection.size();
      }
  
  }
  
  
  

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