001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections4.iterators;
018
019import java.util.NoSuchElementException;
020
021import org.apache.commons.collections4.ResettableIterator;
022
023/**
024 * <code>SingletonIterator</code> is an {@link Iterator} over a single
025 * object instance.
026 *
027 * @since 2.0
028 * @version $Id: SingletonIterator.html 972421 2015-11-14 20:00:04Z tn $
029 */
030public class SingletonIterator<E>
031        implements ResettableIterator<E> {
032
033    /** Whether remove is allowed */
034    private final boolean removeAllowed;
035    /** Is the cursor before the first element */
036    private boolean beforeFirst = true;
037    /** Has the element been removed */
038    private boolean removed = false;
039    /** The object */
040    private E object;
041
042    /**
043     * Constructs a new <code>SingletonIterator</code> where <code>remove</code>
044     * is a permitted operation.
045     *
046     * @param object  the single object to return from the iterator
047     */
048    public SingletonIterator(final E object) {
049        this(object, true);
050    }
051
052    /**
053     * Constructs a new <code>SingletonIterator</code> optionally choosing if
054     * <code>remove</code> is a permitted operation.
055     *
056     * @param object  the single object to return from the iterator
057     * @param removeAllowed  true if remove is allowed
058     * @since 3.1
059     */
060    public SingletonIterator(final E object, final boolean removeAllowed) {
061        super();
062        this.object = object;
063        this.removeAllowed = removeAllowed;
064    }
065
066    //-----------------------------------------------------------------------
067    /**
068     * Is another object available from the iterator?
069     * <p>
070     * This returns true if the single object hasn't been returned yet.
071     *
072     * @return true if the single object hasn't been returned yet
073     */
074    public boolean hasNext() {
075        return beforeFirst && !removed;
076    }
077
078    /**
079     * Get the next object from the iterator.
080     * <p>
081     * This returns the single object if it hasn't been returned yet.
082     *
083     * @return the single object
084     * @throws NoSuchElementException if the single object has already
085     *    been returned
086     */
087    public E next() {
088        if (!beforeFirst || removed) {
089            throw new NoSuchElementException();
090        }
091        beforeFirst = false;
092        return object;
093    }
094
095    /**
096     * Remove the object from this iterator.
097     *
098     * @throws IllegalStateException if the <tt>next</tt> method has not
099     *        yet been called, or the <tt>remove</tt> method has already
100     *        been called after the last call to the <tt>next</tt>
101     *        method.
102     * @throws UnsupportedOperationException if remove is not supported
103     */
104    public void remove() {
105        if (removeAllowed) {
106            if (removed || beforeFirst) {
107                throw new IllegalStateException();
108            }
109            object = null;
110            removed = true;
111        } else {
112            throw new UnsupportedOperationException();
113        }
114    }
115
116    /**
117     * Reset the iterator to the start.
118     */
119    public void reset() {
120        beforeFirst = true;
121    }
122
123}