Update #0 - First Release

sources/main/java/com/google/common/collect/ForwardingQueue.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright (C) 2007 The Guava Authors
+ *
+ * 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 com.google.common.collect;
+
+import java.util.NoSuchElementException;
+import java.util.Queue;
+
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * A queue which forwards all its method calls to another queue. Subclasses
+ * should override one or more methods to modify the behavior of the backing
+ * queue as desired per the
+ * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator
+ * pattern</a>.
+ *
+ * <p>
+ * <b>Warning:</b> The methods of {@code ForwardingQueue} forward
+ * <b>indiscriminately</b> to the methods of the delegate. For example,
+ * overriding {@link #add} alone <b>will not</b> change the behavior of
+ * {@link #offer} which can lead to unexpected behavior. In this case, you
+ * should override {@code offer} as well, either providing your own
+ * implementation, or delegating to the provided {@code standardOffer} method.
+ *
+ * <p>
+ * The {@code standard} methods are not guaranteed to be thread-safe, even when
+ * all of the methods that they depend on are thread-safe.
+ *
+ * @author Mike Bostock
+ * @author Louis Wasserman
+ * @since 2.0 (imported from Google Collections Library)
+ */
+@GwtCompatible
+public abstract class ForwardingQueue<E> extends ForwardingCollection<E> implements Queue<E> {
+
+	/** Constructor for use by subclasses. */
+	protected ForwardingQueue() {
+	}
+
+	@Override
+	protected abstract Queue<E> delegate();
+
+	@Override
+	public boolean offer(E o) {
+		return delegate().offer(o);
+	}
+
+	@Override
+	public E poll() {
+		return delegate().poll();
+	}
+
+	@Override
+	public E remove() {
+		return delegate().remove();
+	}
+
+	@Override
+	public E peek() {
+		return delegate().peek();
+	}
+
+	@Override
+	public E element() {
+		return delegate().element();
+	}
+
+	/**
+	 * A sensible definition of {@link #offer} in terms of {@link #add}. If you
+	 * override {@link #add}, you may wish to override {@link #offer} to forward to
+	 * this implementation.
+	 * 
+	 * @since 7.0
+	 */
+	protected boolean standardOffer(E e) {
+		try {
+			return add(e);
+		} catch (IllegalStateException caught) {
+			return false;
+		}
+	}
+
+	/**
+	 * A sensible definition of {@link #peek} in terms of {@link #element}. If you
+	 * override {@link #element}, you may wish to override {@link #peek} to forward
+	 * to this implementation.
+	 * 
+	 * @since 7.0
+	 */
+	protected E standardPeek() {
+		try {
+			return element();
+		} catch (NoSuchElementException caught) {
+			return null;
+		}
+	}
+
+	/**
+	 * A sensible definition of {@link #poll} in terms of {@link #remove}. If you
+	 * override {@link #remove}, you may wish to override {@link #poll} to forward
+	 * to this implementation.
+	 * 
+	 * @since 7.0
+	 */
+	protected E standardPoll() {
+		try {
+			return remove();
+		} catch (NoSuchElementException caught) {
+			return null;
+		}
+	}
+}