iteratorutils.java

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/*
 *  Copyright 2002-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections;

import java.lang.reflect.Array;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Dictionary;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;

import org.apache.commons.collections.iterators.ArrayIterator;
import org.apache.commons.collections.iterators.ArrayListIterator;
import org.apache.commons.collections.iterators.CollatingIterator;
import org.apache.commons.collections.iterators.EmptyIterator;
import org.apache.commons.collections.iterators.EmptyListIterator;
import org.apache.commons.collections.iterators.EmptyMapIterator;
import org.apache.commons.collections.iterators.EmptyOrderedIterator;
import org.apache.commons.collections.iterators.EmptyOrderedMapIterator;
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.LoopingIterator;
import org.apache.commons.collections.iterators.LoopingListIterator;
import org.apache.commons.collections.iterators.ObjectArrayIterator;
import org.apache.commons.collections.iterators.ObjectArrayListIterator;
import org.apache.commons.collections.iterators.ObjectGraphIterator;
import org.apache.commons.collections.iterators.SingletonIterator;
import org.apache.commons.collections.iterators.SingletonListIterator;
import org.apache.commons.collections.iterators.TransformIterator;
import org.apache.commons.collections.iterators.UnmodifiableIterator;
import org.apache.commons.collections.iterators.UnmodifiableListIterator;
import org.apache.commons.collections.iterators.UnmodifiableMapIterator;

/**
 * Provides static utility methods and decorators for {@link Iterator} 
 * instances. The implementations are provided in the iterators subpackage.
 * <p>
 * WARNING: Due to human error certain binary incompatabilities were introduced
 * between Commons Collections 2.1 and 3.0. The class remained source and test
 * compatible, so if you can recompile all your classes and dependencies
 * everything is OK. Those methods which are binary incompatible are marked as
 * such, together with alternate solutions that are binary compatible
 * against versions 2.1.1 and 3.1.
 *
 * @since Commons Collections 2.1
 * @version $Revision: 405920 $ $Date: 2006-05-12 23:48:04 +0100 (Fri, 12 May 2006) $
 * 
 * @author Stephen Colebourne
 * @author Phil Steitz
 */
public class IteratorUtils {
    // validation is done in this class in certain cases because the
    // public classes allow invalid states

    /**
     * An iterator over no elements.
     * <p>
     * WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>EmptyIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1.
     */
    public static final ResettableIterator EMPTY_ITERATOR = EmptyIterator.RESETTABLE_INSTANCE;
    /**
     * A list iterator over no elements.
     * <p>
     * WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>EmptyListIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1.
     */
    public static final ResettableListIterator EMPTY_LIST_ITERATOR = EmptyListIterator.RESETTABLE_INSTANCE;
    /**
     * An ordered iterator over no elements.
     */    
    public static final OrderedIterator EMPTY_ORDERED_ITERATOR = EmptyOrderedIterator.INSTANCE;
    /**
     * A map iterator over no elements.
     */    
    public static final MapIterator EMPTY_MAP_ITERATOR = EmptyMapIterator.INSTANCE;
    /**
     * An ordered map iterator over no elements.
     */    
    public static final OrderedMapIterator EMPTY_ORDERED_MAP_ITERATOR = EmptyOrderedMapIterator.INSTANCE;

    /**
     * IteratorUtils is not normally instantiated.
     */
    public IteratorUtils() {
    }

    // Empty
    //-----------------------------------------------------------------------
    /**
     * Gets an empty iterator.
     * <p>
     * This iterator is a valid iterator object that will iterate over
     * nothing.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>EmptyIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1.
     *
     * @return  an iterator over nothing
     */
    public static ResettableIterator emptyIterator() {
        return EMPTY_ITERATOR;
    }

    /**
     * Gets an empty list iterator.
     * <p>
     * This iterator is a valid list iterator object that will iterate 
     * over nothing.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>EmptyListIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1.
     *
     * @return  a list iterator over nothing
     */
    public static ResettableListIterator emptyListIterator() {
        return EMPTY_LIST_ITERATOR;
    }

    /**
     * Gets an empty ordered iterator.
     * <p>
     * This iterator is a valid iterator object that will iterate 
     * over nothing.
     *
     * @return  an ordered iterator over nothing
     */
    public static OrderedIterator emptyOrderedIterator() {
        return EMPTY_ORDERED_ITERATOR;
    }

    /**
     * Gets an empty map iterator.
     * <p>
     * This iterator is a valid map iterator object that will iterate 
     * over nothing.
     *
     * @return  a map iterator over nothing
     */
    public static MapIterator emptyMapIterator() {
        return EMPTY_MAP_ITERATOR;
    }

    /**
     * Gets an empty ordered map iterator.
     * <p>
     * This iterator is a valid map iterator object that will iterate 
     * over nothing.
     *
     * @return  a map iterator over nothing
     */
    public static OrderedMapIterator emptyOrderedMapIterator() {
        return EMPTY_ORDERED_MAP_ITERATOR;
    }

    // Singleton
    //-----------------------------------------------------------------------
    /**
     * Gets a singleton iterator.
     * <p>
     * This iterator is a valid iterator object that will iterate over
     * the specified object.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>new SingletonIterator(object)</code> for compatability.
     *
     * @param object  the single object over which to iterate
     * @return  a singleton iterator over the object
     */
    public static ResettableIterator 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);
    }

    // Arrays
    //-----------------------------------------------------------------------
    /**
     * Gets an iterator over an object array.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>new ArrayIterator(array)</code> for compatability.
     *
     * @param array  the array over which to iterate
     * @return  an iterator over the array
     * @throws NullPointerException if array is null
     */
    public static ResettableIterator arrayIterator(Object[] array) {
        return new ObjectArrayIterator(array);
    }

    /**
     * Gets an iterator over an object or primitive array.
     * <p>
     * This method will handle primitive arrays as well as object arrays.
     * The primitives will be wrapped in the appropriate wrapper class.
     *
     * @param array  the array over which to iterate
     * @return  an iterator over the array
     * @throws IllegalArgumentException if the array is not an array
     * @throws NullPointerException if array is null
     */
    public static ResettableIterator arrayIterator(Object array) {
        return new ArrayIterator(array);
    }

    /**
     * Gets an iterator over the end part of an object array.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>new ArrayIterator(array,start)</code> for compatability.
     *
     * @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 IndexOutOfBoundsException if start is less than zero or greater
     *  than the length of the array
     * @throws NullPointerException if array is null
     */
    public static ResettableIterator arrayIterator(Object[] array, int start) {
        return new ObjectArrayIterator(array, start);
    }

    /**
     * Gets an iterator over the end part of an object or primitive array.
     * <p>
     * This method will handle primitive arrays as well as object arrays.
     * The primitives will be wrapped in the appropriate wrapper class.
     *
     * @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 the array is not an array
     * @throws IndexOutOfBoundsException if start is less than zero or greater
     *  than the length of the array
     * @throws NullPointerException if array is null
     */
    public static ResettableIterator arrayIterator(Object array, int start) {
        return new ArrayIterator(array, start);
    }

    /**
     * Gets an iterator over part of an object array.
     * <p>
     * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1.
     * Use <code>new ArrayIterator(array,start,end)</code> for compatability.
     *
     * @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 IndexOutOfBoundsException if array bounds are invalid
     * @throws IllegalArgumentException if end is before start
     * @throws NullPointerException if array is null
     */
    public static ResettableIterator arrayIterator(Object[] array, int start, int end) {
        return new ObjectArrayIterator(array, start, end);
    }

    /**
     * Gets an iterator over part of an object or primitive array.
     * <p>
     * This method will handle primitive arrays as well as object arrays.
     * The primitives will be wrapped in the appropriate wrapper class.
     *
     * @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 the array is not an array
     * @throws IndexOutOfBoundsException if array bounds are invalid
     * @throws IllegalArgumentException if end is before start