SingletonIterator.java
- /*
- * 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.ResettableIterator;
- /**
- * {@code SingletonIterator} is an {@link java.util.Iterator} over a single
- * object instance.
- *
- * @param <E> the type of elements returned by this iterator.
- * @since 2.0
- */
- public class SingletonIterator<E>
- implements ResettableIterator<E> {
- /** 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;
- /** The object */
- private E object;
- /**
- * Constructs a new {@code SingletonIterator} where {@code remove}
- * is a permitted operation.
- *
- * @param object the single object to return from the iterator
- */
- public SingletonIterator(final E 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 3.1
- */
- public SingletonIterator(final E object, final boolean removeAllowed) {
- 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
- */
- @Override
- public boolean hasNext() {
- return beforeFirst && !removed;
- }
- /**
- * Gets 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;
- return object;
- }
- /**
- * Remove the object from this iterator.
- *
- * @throws IllegalStateException if the {@code next} method has not
- * yet been called, or the {@code remove} method has already
- * been called after the last call to the {@code next}
- * method.
- * @throws UnsupportedOperationException if remove is not supported
- */
- @Override
- public void remove() {
- if (!removeAllowed) {
- throw new UnsupportedOperationException();
- }
- if (removed || beforeFirst) {
- throw new IllegalStateException();
- }
- object = null;
- removed = true;
- }
- /**
- * Reset the iterator to the start.
- */
- @Override
- public void reset() {
- beforeFirst = true;
- }
- }