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/*
* 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 com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.NoSuchElementException;
import java.util.Queue;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* 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 decorator pattern.
*
* Warning: The methods of {@code ForwardingQueue} forward indiscriminately to the
* methods of the delegate. For example, overriding {@link #add} alone will not 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.
*
*
{@code default} method warning: This class does not forward calls to {@code
* default} methods. Instead, it inherits their default implementations. When those implementations
* invoke methods, they invoke methods on the {@code ForwardingQueue}.
*
*
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
*/
@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingQueue extends ForwardingCollection
implements Queue {
/** Constructor for use by subclasses. */
protected ForwardingQueue() {}
@Override
protected abstract Queue delegate();
@CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
@Override
public boolean offer(@ParametricNullness E o) {
return delegate().offer(o);
}
@CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
@Override
@CheckForNull
public E poll() {
return delegate().poll();
}
@CanIgnoreReturnValue
@Override
@ParametricNullness
public E remove() {
return delegate().remove();
}
@Override
@CheckForNull
public E peek() {
return delegate().peek();
}
@Override
@ParametricNullness
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(@ParametricNullness 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
*/
@CheckForNull
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
*/
@CheckForNull
protected E standardPoll() {
try {
return remove();
} catch (NoSuchElementException caught) {
return null;
}
}
}