- /*
- * Copyright 1999-2004 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.iterators;
-
- import java.util.ListIterator;
- import java.util.NoSuchElementException;
-
- import org.apache.commons.collections.ResettableListIterator;
-
- /**
- * <code>SingletonIterator</code> is an {@link ListIterator} over a single
- * object instance.
- *
- * @since Commons Collections 2.1
- * @version $Revision: 1.13 $ $Date: 2004/02/18 00:59:50 $
- *
- * @author Stephen Colebourne
- * @author Rodney Waldhoff
- */
- public class SingletonListIterator implements ListIterator, ResettableListIterator {
-
- private boolean beforeFirst = true;
- private boolean nextCalled = false;
- private boolean removed = false;
- private Object object;
-
- /**
- * Constructs a new <code>SingletonListIterator</code>.
- *
- * @param object the single object to return from the iterator
- */
- public SingletonListIterator(Object object) {
- super();
- this.object = object;
- }
-
- /**
- * 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;
- }
-
- /**
- * Is a previous object available from the iterator?
- * <p>
- * This returns true if the single object has been returned.
- *
- * @return true if the single object has been returned
- */
- public boolean hasPrevious() {
- return !beforeFirst && !removed;
- }
-
- /**
- * Returns the index of the element that would be returned by a subsequent
- * call to <tt>next</tt>.
- *
- * @return 0 or 1 depending on current state.
- */
- public int nextIndex() {
- return (beforeFirst ? 0 : 1);
- }
-
- /**
- * Returns the index of the element that would be returned by a subsequent
- * call to <tt>previous</tt>. A return value of -1 indicates that the iterator is currently at
- * the start.
- *
- * @return 0 or -1 depending on current state.
- */
- public int previousIndex() {
- return (beforeFirst ? -1 : 0);
- }
-
- /**
- * 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;
- nextCalled = true;
- return object;
- }
-
- /**
- * Get the previous object from the iterator.
- * <p>
- * This returns the single object if it has been returned.
- *
- * @return the single object
- * @throws NoSuchElementException if the single object has not already
- * been returned
- */
- public Object previous() {
- if (beforeFirst || removed) {
- throw new NoSuchElementException();
- }
- beforeFirst = true;
- return object;
- }
-
- /**
- * Remove the object from this iterator.
- * @throws IllegalStateException if the <tt>next</tt> or <tt>previous</tt>
- * method has not yet been called, or the <tt>remove</tt> method
- * has already been called after the last call to <tt>next</tt>
- * or <tt>previous</tt>.
- */
- public void remove() {
- if(!nextCalled || removed) {
- throw new IllegalStateException();
- } else {
- object = null;
- removed = true;
- }
- }
-
- /**
- * Add always throws {@link UnsupportedOperationException}.
- *
- * @throws UnsupportedOperationException always
- */
- public void add(Object obj) {
- throw new UnsupportedOperationException("add() is not supported by this iterator");
- }
-
- /**
- * Set sets the value of the singleton.
- *
- * @param obj the object to set
- * @throws IllegalStateException if <tt>next</tt> has not been called
- * or the object has been removed
- */
- public void set(Object obj) {
- if (!nextCalled || removed) {
- throw new IllegalStateException();
- }
- this.object = obj;
- }
-
- /**
- * Reset the iterator back to the start.
- */
- public void reset() {
- beforeFirst = true;
- nextCalled = false;
- }
-
- }