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From scolebou...@apache.org
Subject cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections IteratorUtils.java
Date Sat, 17 Aug 2002 11:38:53 GMT
scolebourne    2002/08/17 04:38:53

  Added:       collections/src/java/org/apache/commons/collections
                        IteratorUtils.java
  Log:
  Initial checkin
  
  Revision  Changes    Path
  1.1                  jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorUtils.java
  
  Index: IteratorUtils.java
  ===================================================================
  /*
   * $Header: /home/cvs/jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorUtils.java,v
1.1 2002/08/17 11:38:53 scolebourne Exp $
   * $Revision: 1.1 $
   * $Date: 2002/08/17 11:38:53 $
   *
   * ====================================================================
   *
   * 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.lang.reflect.Method;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.Dictionary;
  import java.util.Enumeration;
  import java.util.Iterator;
  import java.util.ListIterator;
  import java.util.Map;
  
  import org.apache.commons.collections.iterators.ArrayIterator;
  import org.apache.commons.collections.iterators.CollatingIterator;
  import org.apache.commons.collections.iterators.EnumerationIterator;
  import org.apache.commons.collections.iterators.FilterIterator;
  import org.apache.commons.collections.iterators.FilterListIterator;
  import org.apache.commons.collections.iterators.IteratorChain;
  import org.apache.commons.collections.iterators.IteratorEnumeration;
  import org.apache.commons.collections.iterators.ListIteratorWrapper;
  import org.apache.commons.collections.iterators.SingletonIterator;
  import org.apache.commons.collections.iterators.SingletonListIterator;
  import org.apache.commons.collections.iterators.TransformIterator;
  /**
   * Provides static utility methods and decorators for {@link Iterator} 
   * instances. The implementations are provided in the 
   * <code>org.apache.commons.collections.iterators</code> subpackage.
   *
   * @author <a href="mailto:scolebourne@joda.org">Stephen Colebourne</a>
   * @version $Id: IteratorUtils.java,v 1.1 2002/08/17 11:38:53 scolebourne Exp $
   * @since 2.1
   */
  public class IteratorUtils {
      // validation is done in this class in certain cases because the
      // public classes allow invalid states
  
      /**
       * Prevents instantiation.
       */
      private IteratorUtils() {
      }
  
      /**
       * Gets an empty iterator.
       * <p>
       * This iterator is a valid iterator object that will iterate over
       * nothing.
       *
       * @return  an iterator over nothing
       */
      public static Iterator emptyIterator() {
          return Collections.EMPTY_LIST.iterator();
      }
  
      /**
       * Gets an empty list iterator.
       * <p>
       * This iterator is a valid list iterator object that will iterate 
       * over nothing.
       *
       * @return  a list iterator over nothing
       */
      public static ListIterator emptyListIterator() {
          return Collections.EMPTY_LIST.listIterator();
      }
  
      /**
       * Gets a singleton iterator.
       * <p>
       * This iterator is a valid iterator object that will iterate over
       * the specified object.
       *
       * @param object  the single object over which to iterate
       * @return  a singleton iterator over the object
       */
      public static Iterator singletonIterator(Object object) {
          return new SingletonIterator(object);
      }
  
      /**
       * Gets a singleton list iterator.
       * <p>
       * This iterator is a valid list iterator object that will iterate over
       * the specified object.
       *
       * @param object  the single object over which to iterate
       * @return  a singleton list iterator over the object
       */
      public static ListIterator singletonListIterator(Object object) {
          return new SingletonListIterator(object);
      }
  
      /**
       * Gets an iterator over an array.
       *
       * @param array  the array over which to iterate
       * @return  an iterator over the array
       * @throws NullPointerException if array is null
       */
      public static Iterator arrayIterator(Object[] array) {
          return new ArrayIterator(array);
      }
  
      /**
       * Gets an iterator over the end part of an array.
       *
       * @param array  the array over which to iterate
       * @param start  the index to start iterating at
       * @return an iterator over part of the array
       * @throws IllegalArgumentException if array bounds are invalid
       * @throws NullPointerException if array is null
       */
      public static Iterator arrayIterator(Object[] array, int start) {
          return new ArrayIterator(array, start);
      }
  
      /**
       * Gets an iterator over part of an array.
       *
       * @param array  the array over which to iterate
       * @param start  the index to start iterating at
       * @param end  the index to finish iterating at
       * @return an iterator over part of the array
       * @throws IllegalArgumentException if array bounds are invalid
       * @throws NullPointerException if array is null
       */
      public static Iterator arrayIterator(Object[] array, int start, int end) {
          return new ArrayIterator(array, start, end);
      }
  
  //    /**
  //     * Gets a list iterator over an array.
  //     *
  //     * @param array  the array over which to iterate
  //     * @return  a list iterator over the array
  //     * @throws NullPointerException if array is null
  //     */
  //    public static ListIterator arrayListIterator(Object[] array) {
  //        return new ArrayListIterator(array);
  //    }
  //
  //    /**
  //     * Gets a list iterator over the end part of an array.
  //     *
  //     * @param array  the array over which to iterate
  //     * @param start  the index to start iterating at
  //     * @return a list iterator over part of the array
  //     * @throws IllegalArgumentException if array bounds are invalid
  //     * @throws NullPointerException if array is null
  //     */
  //    public static ListIterator arrayListIterator(Object[] array, int start) {
  //        return new ArrayListIterator(array, start);
  //    }
  //
  //    /**
  //     * Gets a list iterator over part of an array.
  //     *
  //     * @param array  the array over which to iterate
  //     * @param start  the index to start iterating at
  //     * @param end  the index to finish iterating at
  //     * @return a list iterator over part of the array
  //     * @throws IllegalArgumentException if array bounds are invalid
  //     * @throws NullPointerException if array is null
  //     */
  //    public static ListIterator arrayListIterator(Object[] array, int start, int end) {
  //        return new ArrayListIterator(array, start, end);
  //    }
  
      /**
       * Gets an iterator that iterates through two {@link Iterator}s 
       * one after another.
       *
       * @param iterator1  the first iterators to use, not null
       * @param iterator2  the first iterators to use, not null
       * @return a combination iterator over the iterators
       * @throws NullPointerException if either iterator is null
       */
      public static Iterator chainedIterator(Iterator iterator1, Iterator iterator2) {
          return new IteratorChain(iterator1, iterator2);
      }
  
      /**
       * Gets an iterator that iterates through an array of {@link Iterator}s 
       * one after another.
       *
       * @param iterators  the iterators to use, not null or empty or contain nulls
       * @return a combination iterator over the iterators
       * @throws NullPointerException if iterators array is null or contains a null
       */
      public static Iterator chainedIterator(Iterator[] iterators) {
          return new IteratorChain(iterators);
      }
  
      /**
       * Gets an iterator that iterates through a collections of {@link Iterator}s 
       * one after another.
       *
       * @param iterators  the iterators to use, not null or empty or contain nulls
       * @return a combination iterator over the iterators
       * @throws NullPointerException if iterators collection is null or contains a null
       * @throws ClassCastException if the iterators collection contains the wrong object
type
       */
      public static Iterator chainedIterator(Collection iterators) {
          return new IteratorChain(iterators);
      }
  
      /**
       * Gets an iterator that provides an ordered iteration over the elements
       * contained in a collection of ordered {@link Iterator}s.
       * <p>
       * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>,
       * the {@link #next} method will return the lesser of 
       * <code>A.next()</code> and <code>B.next()</code>.
       * <p>
       * The comparator is optional. If null is specified then natural order is used.
       *
       * @param comparator  the comparator to use, may be null for natural order
       * @param iterator1  the first iterators to use, not null
       * @param iterator2  the first iterators to use, not null
       * @return a combination iterator over the iterators
       * @throws NullPointerException if either iterator is null
       */
      public static Iterator collatedIterator(Comparator comparator, Iterator iterator1, Iterator
iterator2) {
          return new CollatingIterator(comparator, iterator1, iterator2);
      }
  
      /**
       * Gets an iterator that provides an ordered iteration over the elements
       * contained in an array of {@link Iterator}s.
       * <p>
       * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>,
       * the {@link #next} method will return the lesser of 
       * <code>A.next()</code> and <code>B.next()</code> and so on.
       * <p>
       * The comparator is optional. If null is specified then natural order is used.
       *
       * @param comparator  the comparator to use, may be null for natural order
       * @param iterators  the iterators to use, not null or empty or contain nulls
       * @return a combination iterator over the iterators
       * @throws NullPointerException if iterators array is null or contains a null
       */
      public static Iterator collatedIterator(Comparator comparator, Iterator[] iterators)
{
          return new CollatingIterator(comparator, iterators);
      }
  
      /**
       * Gets an iterator that provides an ordered iteration over the elements
       * contained in a collection of {@link Iterator}s.
       * <p>
       * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>,
       * the {@link #next} method will return the lesser of 
       * <code>A.next()</code> and <code>B.next()</code> and so on.
       * <p>
       * The comparator is optional. If null is specified then natural order is used.
       *
       * @param comparator  the comparator to use, may be null for natural order
       * @param iterators  the iterators to use, not null or empty or contain nulls
       * @return a combination iterator over the iterators
       * @throws NullPointerException if iterators collection is null or contains a null
       * @throws ClassCastException if the iterators collection contains the wrong object
type
       */
      public static Iterator collatedIterator(Comparator comparator, Collection iterators)
{
          return new CollatingIterator(comparator, iterators);
      }
  
      /**
       * Gets an iterator that transforms the elements of another iterator.
       * <p>
       * The transformation occurs during the next() method and the underlying
       * iterator is unaffected by the transformation.
       *
       * @param iterator  the iterator to use, not null
       * @param transform  the transform to use, not null
       * @throws NullPointerException if either parameter is null
       */
      public static Iterator transformedIterator(Iterator iterator, Transformer transform)
{
          if (iterator == null) {
              throw new NullPointerException("Iterator must not be null");
          }
          if (transform == null) {
              throw new NullPointerException("Transformer must not be null");
          }
          return new TransformIterator(iterator, transform);
      }
      
      /**
       * Gets an iterator that filters another iterator.
       * <p>
       * The returned iterator will only return objects that match the specified
       * filtering predicate.
       *
       * @param iterator  the iterator to use, not null
       * @param predicate  the predicate to use as a filter, not null
       * @throws NullPointerException if either parameter is null
       */
      public static Iterator filteredIterator(Iterator iterator, Predicate predicate) {
          if (iterator == null) {
              throw new NullPointerException("Iterator must not be null");
          }
          if (predicate == null) {
              throw new NullPointerException("Predicate must not be null");
          }
          return new FilterIterator(iterator, predicate);
      }
      
      /**
       * Gets a list iterator that filters another list iterator.
       * <p>
       * The returned iterator will only return objects that match the specified
       * filtering predicate.
       *
       * @param listIterator  the list iterator to use, not null
       * @param predicate  the predicate to use as a filter, not null
       * @throws NullPointerException if either parameter is null
       */
      public static ListIterator filteredListIterator(ListIterator listIterator, Predicate
predicate) {
          if (listIterator == null) {
              throw new NullPointerException("ListIterator must not be null");
          }
          if (predicate == null) {
              throw new NullPointerException("Predicate must not be null");
          }
          return new FilterListIterator(listIterator, predicate);
      }
      
      /**
       * Gets a list iterator based on a simple iterator.
       * <p>
       * As the wrapped Iterator is traversed, a LinkedList of its values is
       * cached, permitting all required operations of ListIterator.
       *
       * @param iterator  the iterator to use, not null
       * @throws NullPointerException if iterator parameter is null
       */
      public static Iterator iteratorListIterator(Iterator iterator) {
          return new ListIteratorWrapper(iterator);
      }
      
      /**
       * Gets an iterator that provides an iterator view of the given enumeration.
       *
       * @param enumeration  the enumeration to use
       */
      public static Iterator enumerationIterator(Enumeration enumeration) {
          if (enumeration == null) {
              throw new NullPointerException("Enumeration must not be null");
          }
          return new EnumerationIterator(enumeration);
      }
  
      /**
       * Gets an iterator that provides an iterator view of the given enumeration 
       * that will remove elements from the specified collection.
       *
       * @param enumeration  the enumeration to use
       * @param collection  the collection to remove elements form
       */
      public static Iterator enumerationIterator(Enumeration enumeration, Collection removeCollection)
{
          if (enumeration == null) {
              throw new NullPointerException("Enumeration must not be null");
          }
          if (removeCollection == null) {
              throw new NullPointerException("Collection must not be null");
          }
          return new EnumerationIterator(enumeration, removeCollection);
      }
      
      /**
       * Gets an enumeration that wraps an iterator.
       *
       * @param iterator  the iterator to use, not null
       * @throws NullPointerException if iterator is null
       */
      public static Enumeration iteratorEnumeration(Iterator iterator) {
          if (iterator == null) {
              throw new NullPointerException("Iterator must not be null");
          }
          return new IteratorEnumeration(iterator);
      }
      
      /** 
       * Gets a suitable Iterator for the given object.
       * <p>
       * This method can handles objects as follows
       * <ul>
       * <li>null - empty iterator
       * <li>Iterator - returned directly
       * <li>Enumeration - wrapped
       * <li>Collection - iterator from collection returned
       * <li>Map - values iterator returned
       * <li>Dictionary - values (elements) enumeration returned as iterator
       * <li>array - iterator over array returned
       * <li>object with iterator() public method accessed by reflection
       * <li>object - singleton iterator
       * </ul>
       * 
       * @param obj  the object to convert to an iterator
       * @return a suitable iterator, never null
       */
      public static Iterator getIterator(Object obj) {
          if (obj == null) {
              return emptyIterator();
              
          } else if (obj instanceof Iterator) {
              return (Iterator) obj;
              
          } else if (obj instanceof Collection) {
              return ((Collection) obj).iterator();
              
          } else if (obj instanceof Object[]) {
              return new ArrayIterator(obj);
              
          } else if (obj instanceof Enumeration) {
              return new EnumerationIterator((Enumeration) obj);
              
          } else if (obj instanceof Map) {
              return ((Map) obj).values().iterator();
              
          } else if (obj instanceof Dictionary) {
              return new EnumerationIterator(((Dictionary) obj).elements());
              
          } else if (obj != null && obj.getClass().isArray()) {
              return new ArrayIterator(obj);
              
          } else {
              try {
                  Method method = obj.getClass().getMethod("iterator", null);
                  if (Iterator.class.isAssignableFrom(method.getReturnType())) {
                      Iterator it = (Iterator) method.invoke(obj, null);
                      if (it != null) {
                          return it;
                      }
                  }
              } catch (Exception ex) {
                  // ignore
              }
              return singletonIterator(obj);
          }
      }
  
  }
  
  
  

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