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Commons Collections example source code file (SingletonIterator.java)

This example Commons Collections source code file (SingletonIterator.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

illegalstateexception, iterator, iterator, nosuchelementexception, object, object, resettableiterator, singletoniterator, singletoniterator, unsupportedoperationexception, unsupportedoperationexception, util

The Commons Collections SingletonIterator.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.Iterator;
import java.util.NoSuchElementException;

import org.apache.commons.collections.ResettableIterator;

/** 
 * <code>SingletonIterator is an {@link Iterator} over a single 
 * object instance.
 *
 * @since Commons Collections 2.0
 * @version $Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $
 * 
 * @author James Strachan
 * @author Stephen Colebourne
 * @author Rodney Waldhoff
 */
public class SingletonIterator
        implements Iterator, ResettableIterator {

    /** Whether remove is allowed */
    private final boolean removeAllowed;
    /** Is the cursor before the first element */
    private boolean beforeFirst = true;
    /** Has the element been removed */
    private boolean removed = false;
    /** The object */
    private Object object;

    /**
     * Constructs a new <code>SingletonIterator where remove
     * is a permitted operation.
     *
     * @param object  the single object to return from the iterator
     */
    public SingletonIterator(Object object) {
        this(object, true);
    }

    /**
     * Constructs a new <code>SingletonIterator optionally choosing if
     * <code>remove is a permitted operation.
     *
     * @param object  the single object to return from the iterator
     * @param removeAllowed  true if remove is allowed
     * @since Commons Collections 3.1
     */
    public SingletonIterator(Object object, boolean removeAllowed) {
        super();
        this.object = object;
        this.removeAllowed = removeAllowed;
    }

    //-----------------------------------------------------------------------
    /**
     * Is another object available from the iterator?
     * <p>
     * This returns true if the single object hasn't been returned yet.
     * 
     * @return true if the single object hasn't been returned yet
     */
    public boolean hasNext() {
        return (beforeFirst && !removed);
    }

    /**
     * Get the next object from the iterator.
     * <p>
     * This returns the single object if it hasn't been returned yet.
     *
     * @return the single object
     * @throws NoSuchElementException if the single object has already 
     *    been returned
     */
    public Object next() {
        if (!beforeFirst || removed) {
            throw new NoSuchElementException();
        }
        beforeFirst = false;
        return object;
    }

    /**
     * Remove the object from this iterator.
     * 
     * @throws IllegalStateException if the <tt>next method has not
     *        yet been called, or the <tt>remove method has already
     *        been called after the last call to the <tt>next
     *        method.
     * @throws UnsupportedOperationException if remove is not supported
     */
    public void remove() {
        if (removeAllowed) {
            if (removed || beforeFirst) {
                throw new IllegalStateException();
            } else {
                object = null;
                removed = true;
            }
        } else {
            throw new UnsupportedOperationException();
        }
    }
    
    /**
     * Reset the iterator to the start.
     */
    public void reset() {
        beforeFirst = true;
    }
    
}

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