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/*
* 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.ListIterator;
import java.util.NoSuchElementException;
import org.apache.commons.collections.ResettableListIterator;
/**
* SingletonIterator is an {@link ListIterator} over a single
* object instance.
*
* @since Commons Collections 2.1
* @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
*
* @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 SingletonListIterator.
*
* @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?
*
* 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?
*
* 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 next.
*
* @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 previous. 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.
*
* 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.
*
* 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 next or previous
* method has not yet been called, or the remove method
* has already been called after the last call to next
* or previous.
*/
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 next 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;
}
}