UnmodifiableQueue.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.queue;
- import java.io.IOException;
- import java.io.ObjectInputStream;
- import java.io.ObjectOutputStream;
- import java.util.Collection;
- import java.util.Iterator;
- import java.util.Queue;
- import java.util.function.Predicate;
- import org.apache.commons.collections4.Unmodifiable;
- import org.apache.commons.collections4.iterators.UnmodifiableIterator;
- /**
- * Decorates another {@link Queue} to ensure it can't be altered.
- * <p>
- * Attempts to modify it will result in an UnsupportedOperationException.
- * </p>
- *
- * @param <E> the type of elements held in this queue
- * @since 4.0
- */
- public final class UnmodifiableQueue<E>
- extends AbstractQueueDecorator<E>
- implements Unmodifiable {
- /** Serialization version */
- private static final long serialVersionUID = 1832948656215393357L;
- /**
- * Factory method to create an unmodifiable queue.
- * <p>
- * If the queue passed in is already unmodifiable, it is returned.
- *
- * @param <E> the type of the elements in the queue
- * @param queue the queue to decorate, must not be null
- * @return an unmodifiable Queue
- * @throws NullPointerException if queue is null
- */
- public static <E> Queue<E> unmodifiableQueue(final Queue<? extends E> queue) {
- if (queue instanceof Unmodifiable) {
- @SuppressWarnings("unchecked") // safe to upcast
- final Queue<E> tmpQueue = (Queue<E>) queue;
- return tmpQueue;
- }
- return new UnmodifiableQueue<>(queue);
- }
- /**
- * Constructor that wraps (not copies).
- *
- * @param queue the queue to decorate, must not be null
- * @throws NullPointerException if queue is null
- */
- @SuppressWarnings("unchecked") // safe to upcast
- private UnmodifiableQueue(final Queue<? extends E> queue) {
- super((Queue<E>) queue);
- }
- @Override
- public boolean add(final Object object) {
- throw new UnsupportedOperationException();
- }
- @Override
- public boolean addAll(final Collection<? extends E> coll) {
- throw new UnsupportedOperationException();
- }
- @Override
- public void clear() {
- throw new UnsupportedOperationException();
- }
- @Override
- public Iterator<E> iterator() {
- return UnmodifiableIterator.unmodifiableIterator(decorated().iterator());
- }
- @Override
- public boolean offer(final E obj) {
- throw new UnsupportedOperationException();
- }
- @Override
- public E poll() {
- throw new UnsupportedOperationException();
- }
- /**
- * Deserializes the collection in using a custom routine.
- *
- * @param in the input stream
- * @throws IOException if an I/O error occurs while reading from the input stream
- * @throws ClassNotFoundException if the class of a serialized object cannot be found
- */
- @SuppressWarnings("unchecked")
- private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
- in.defaultReadObject();
- setCollection((Collection<E>) in.readObject());
- }
- @Override
- public E remove() {
- throw new UnsupportedOperationException();
- }
- @Override
- public boolean remove(final Object object) {
- throw new UnsupportedOperationException();
- }
- @Override
- public boolean removeAll(final Collection<?> coll) {
- throw new UnsupportedOperationException();
- }
- /**
- * @since 4.4
- */
- @Override
- public boolean removeIf(final Predicate<? super E> filter) {
- throw new UnsupportedOperationException();
- }
- @Override
- public boolean retainAll(final Collection<?> coll) {
- throw new UnsupportedOperationException();
- }
- /**
- * Serializes this object to an ObjectOutputStream.
- *
- * @param out the target ObjectOutputStream.
- * @throws IOException thrown when an I/O errors occur writing to the target stream.
- */
- private void writeObject(final ObjectOutputStream out) throws IOException {
- out.defaultWriteObject();
- out.writeObject(decorated());
- }
- }