Package com.google.common.collect

Class ForwardingQueue<E extends @Nullable Object>

java.lang.Object

com.google.common.collect.ForwardingObject

com.google.common.collect.ForwardingCollection<E>

com.google.common.collect.ForwardingQueue<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>, Queue<E>

Direct Known Subclasses:

EvictingQueue, ForwardingBlockingQueue, ForwardingDeque

@GwtCompatible
public abstract class ForwardingQueue<E extends @Nullable Object>
extends ForwardingCollection<E>
implements Queue<E>

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 ForwardingQueue forward indiscriminately to the methods of the delegate. For example, overriding ForwardingCollection.add(E) alone will not change the behavior of offer(E) which can lead to unexpected behavior. In this case, you should override offer as well, either providing your own implementation, or delegating to the provided standardOffer method.

default method warning: This class does not forward calls to default methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on the ForwardingQueue.

The standard methods are not guaranteed to be thread-safe, even when all of the methods that they depend on are thread-safe.

Since:

2.0

Author:

Mike Bostock, Louis Wasserman

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	ForwardingQueue()	Constructor for use by subclasses.

Method Summary

Modifier and Type	Method	Description
protected abstract Queue<E>	delegate()	Returns the backing delegate instance that methods are forwarded to.
E	element()	Retrieves, but does not remove, the head of this queue.
boolean	offer(E o)	Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
E	peek()	Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll()	Retrieves and removes the head of this queue, or returns null if this queue is empty.
E	remove()	Retrieves and removes the head of this queue.
protected boolean	standardOffer(E e)	A sensible definition of offer(E) in terms of ForwardingCollection.add(E).
protected E	standardPeek()	A sensible definition of peek() in terms of element().
protected E	standardPoll()	A sensible definition of poll() in terms of remove().

Methods inherited from class com.google.common.collect.ForwardingCollection

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, removeAll, retainAll, size, standardAddAll, standardClear, standardContains, standardContainsAll, standardIsEmpty, standardRemove, standardRemoveAll, standardRetainAll, standardToArray, standardToArray, standardToString, toArray, toArray

Methods inherited from class com.google.common.collect.ForwardingObject

toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, remove, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Methods inherited from interface java.util.Queue

add

Constructor Detail

ForwardingQueue

protected ForwardingQueue()

Constructor for use by subclasses.

Method Detail

delegate

protected abstract Queue<E> delegate()

Description copied from class: ForwardingObject

Returns the backing delegate instance that methods are forwarded to. Abstract subclasses generally override this method with an abstract method that has a more specific return type, such as ForwardingSet.delegate(). Concrete subclasses override this method to supply the instance being decorated.

Specified by:

delegate in class ForwardingCollection<E extends @Nullable Object>

offer

@CanIgnoreReturnValue
public boolean offer(E o)

Description copied from interface: java.util.Queue

Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions. When using a capacity-restricted queue, this method is generally preferable to Queue.add(E), which can fail to insert an element only by throwing an exception.

Specified by:

offer in interface Queue<E extends @Nullable Object>

Parameters:

o - the element to add

Returns:

true if the element was added to this queue, else false

poll

@CanIgnoreReturnValue
@CheckForNull
public E poll()

Description copied from interface: java.util.Queue

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Specified by:

poll in interface Queue<E extends @Nullable Object>

Returns:

the head of this queue, or null if this queue is empty

remove

@CanIgnoreReturnValue
public E remove()

Description copied from interface: java.util.Queue

Retrieves and removes the head of this queue. This method differs from poll() only in that it throws an exception if this queue is empty.

Specified by:

remove in interface Queue<E extends @Nullable Object>

Returns:

the head of this queue

peek

@CheckForNull
public E peek()

Description copied from interface: java.util.Queue

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

Specified by:

peek in interface Queue<E extends @Nullable Object>

Returns:

the head of this queue, or null if this queue is empty

element

public E element()

Description copied from interface: java.util.Queue

Retrieves, but does not remove, the head of this queue. This method differs from peek only in that it throws an exception if this queue is empty.

Specified by:

element in interface Queue<E extends @Nullable Object>

Returns:

the head of this queue

standardOffer

protected boolean standardOffer(E e)

A sensible definition of offer(E) in terms of ForwardingCollection.add(E). If you override ForwardingCollection.add(E), you may wish to override offer(E) to forward to this implementation.

Since:

7.0

standardPeek

@CheckForNull
protected E standardPeek()

A sensible definition of peek() in terms of element(). If you override element(), you may wish to override peek() to forward to this implementation.

Since:

7.0

standardPoll

@CheckForNull
protected E standardPoll()

A sensible definition of poll() in terms of remove(). If you override remove(), you may wish to override poll() to forward to this implementation.

Since:

7.0