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Commons Collections example source code file (ListIteratorWrapper.java)

This example Commons Collections source code file (ListIteratorWrapper.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

arraylist, iterator, list, listiterator, listiteratorwrapper, listiteratorwrapper, nosuchelementexception, nosuchelementexception, object, object, string, unsupported_operation_message, unsupportedoperationexception, unsupportedoperationexception, util

The Commons Collections ListIteratorWrapper.java source code

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.iterators;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import org.apache.commons.collections.ResettableListIterator;

/**
 * Converts an iterator into a list iterator by caching the returned entries.
 * <p>
 * The <code>ListIterator interface has additional useful methods
 * for navigation - <code>previous() and the index methods.
 * This class allows a regular <code>Iterator to behave as a
 * <code>ListIterator. It achieves this by building a list internally
 * of as the underlying iterator is traversed.
 * <p>
 * The optional operations of <code>ListIterator are not supported.
 * <p>
 * This class implements ResettableListIterator from Commons Collections 3.2.
 *
 * @since Commons Collections 2.1
 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 *
 * @author Morgan Delagrange
 * @author Stephen Colebourne
 */
public class ListIteratorWrapper implements ResettableListIterator {

    /** Message used when remove, set or add are called. */
    private static final String UNSUPPORTED_OPERATION_MESSAGE =
        "ListIteratorWrapper does not support optional operations of ListIterator.";

    /** The underlying iterator being decorated. */
    private final Iterator iterator;
    /** The list being used to cache the iterator. */
    private final List list = new ArrayList();

    /** The current index of this iterator. */
    private int currentIndex = 0;
    /** The current index of the wrapped iterator. */
    private int wrappedIteratorIndex = 0;

    // Constructor
    //-------------------------------------------------------------------------
    /**
     * Constructs a new <code>ListIteratorWrapper that will wrap
     * the given iterator.
     *
     * @param iterator  the iterator to wrap
     * @throws NullPointerException if the iterator is null
     */
    public ListIteratorWrapper(Iterator iterator) {
        super();
        if (iterator == null) {
            throw new NullPointerException("Iterator must not be null");
        }
        this.iterator = iterator;
    }

    // ListIterator interface
    //-------------------------------------------------------------------------
    /**
     * Throws {@link UnsupportedOperationException}.
     *
     * @param obj  the object to add, ignored
     * @throws UnsupportedOperationException always
     */
    public void add(Object obj) throws UnsupportedOperationException {
        throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
    }

    /**
     * Returns true if there are more elements in the iterator.
     *
     * @return true if there are more elements
     */
    public boolean hasNext() {
        if (currentIndex == wrappedIteratorIndex) {
            return iterator.hasNext();
        }
        return true;
    }

    /**
     * Returns true if there are previous elements in the iterator.
     *
     * @return true if there are previous elements
     */
    public boolean hasPrevious() {
        if (currentIndex == 0) {
            return false;
        }
        return true;
    }

    /**
     * Returns the next element from the iterator.
     *
     * @return the next element from the iterator
     * @throws NoSuchElementException if there are no more elements
     */
    public Object next() throws NoSuchElementException {
        if (currentIndex < wrappedIteratorIndex) {
            ++currentIndex;
            return list.get(currentIndex - 1);
        }

        Object retval = iterator.next();
        list.add(retval);
        ++currentIndex;
        ++wrappedIteratorIndex;
        return retval;
    }

    /**
     * Returns in the index of the next element.
     *
     * @return the index of the next element
     */
    public int nextIndex() {
        return currentIndex;
    }

    /**
     * Returns the the previous element.
     *
     * @return the previous element
     * @throws NoSuchElementException  if there are no previous elements
     */
    public Object previous() throws NoSuchElementException {
        if (currentIndex == 0) {
            throw new NoSuchElementException();
        }
        --currentIndex;
        return list.get(currentIndex);    
    }

    /**
     * Returns the index of the previous element.
     *
     * @return  the index of the previous element
     */
    public int previousIndex() {
        return currentIndex - 1;
    }

    /**
     * Throws {@link UnsupportedOperationException}.
     *
     * @throws UnsupportedOperationException always
     */
    public void remove() throws UnsupportedOperationException {
        throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
    }

    /**
     * Throws {@link UnsupportedOperationException}.
     *
     * @param obj  the object to set, ignored
     * @throws UnsupportedOperationException always
     */
    public void set(Object obj) throws UnsupportedOperationException {
        throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
    }

    // ResettableIterator interface
    //-------------------------------------------------------------------------
    /**
     * Resets this iterator back to the position at which the iterator
     * was created.
     *
     * @since Commons Collections 3.2
     */
    public void reset()  {
        currentIndex = 0;
    }

}

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