| /* |
| * 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.collections4.iterators; |
| |
| import java.util.NoSuchElementException; |
| |
| import org.apache.commons.collections4.ResettableListIterator; |
| |
| /** |
| * {@code SingletonIterator} is an {@link java.util.ListIterator} over a single |
| * object instance. |
| * |
| * @param <E> the type of elements returned by this iterator. |
| * @since 2.1 |
| */ |
| public class SingletonListIterator<E> implements ResettableListIterator<E> { |
| |
| private boolean beforeFirst = true; |
| private boolean nextCalled; |
| private boolean removed; |
| private E object; |
| |
| /** |
| * Constructs a new {@code SingletonListIterator}. |
| * |
| * @param object the single object to return from the iterator |
| */ |
| public SingletonListIterator(final E object) { |
| 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 |
| */ |
| @Override |
| 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 |
| */ |
| @Override |
| public boolean hasPrevious() { |
| return !beforeFirst && !removed; |
| } |
| |
| /** |
| * Returns the index of the element that would be returned by a subsequent |
| * call to {@code next}. |
| * |
| * @return 0 or 1 depending on current state. |
| */ |
| @Override |
| public int nextIndex() { |
| return beforeFirst ? 0 : 1; |
| } |
| |
| /** |
| * Returns the index of the element that would be returned by a subsequent |
| * call to {@code previous}. A return value of -1 indicates that the iterator is currently at |
| * the start. |
| * |
| * @return 0 or -1 depending on current state. |
| */ |
| @Override |
| 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 |
| */ |
| @Override |
| public E 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 |
| */ |
| @Override |
| public E previous() { |
| if (beforeFirst || removed) { |
| throw new NoSuchElementException(); |
| } |
| beforeFirst = true; |
| return object; |
| } |
| |
| /** |
| * Remove the object from this iterator. |
| * @throws IllegalStateException if the {@code next} or {@code previous} |
| * method has not yet been called, or the {@code remove} method |
| * has already been called after the last call to {@code next} |
| * or {@code previous}. |
| */ |
| @Override |
| public void remove() { |
| if (!nextCalled || removed) { |
| throw new IllegalStateException(); |
| } |
| object = null; |
| removed = true; |
| } |
| |
| /** |
| * Add always throws {@link UnsupportedOperationException}. |
| * |
| * @param obj the object to add |
| * @throws UnsupportedOperationException always |
| */ |
| @Override |
| public void add(final E 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 {@code next} has not been called |
| * or the object has been removed |
| */ |
| @Override |
| public void set(final E obj) { |
| if (!nextCalled || removed) { |
| throw new IllegalStateException(); |
| } |
| this.object = obj; |
| } |
| |
| /** |
| * Reset the iterator back to the start. |
| */ |
| @Override |
| public void reset() { |
| beforeFirst = true; |
| nextCalled = false; |
| } |
| |
| } |