Package com.google.common.collect
Class ForwardingQueue<E extends @Nullable Object>
- java.lang.Object
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- com.google.common.collect.ForwardingObject
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- com.google.common.collect.ForwardingCollection<E>
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- com.google.common.collect.ForwardingQueue<E>
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- 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, overridingForwardingCollection.add(E)
alone will not change the behavior ofoffer(E)
which can lead to unexpected behavior. In this case, you should overrideoffer
as well, either providing your own implementation, or delegating to the providedstandardOffer
method.default
method warning: This class does not forward calls todefault
methods. Instead, it inherits their default implementations. When those implementations invoke methods, they invoke methods on theForwardingQueue
.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
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Constructor Summary
Constructors Modifier Constructor Description protected
ForwardingQueue()
Constructor for use by subclasses.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods 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 returnsnull
if this queue is empty.E
poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.E
remove()
Retrieves and removes the head of this queue.protected boolean
standardOffer(E e)
A sensible definition ofoffer(E)
in terms ofForwardingCollection.add(E)
.protected E
standardPeek()
protected E
standardPoll()
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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
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Methods inherited from class com.google.common.collect.ForwardingObject
toString
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Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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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
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Constructor Detail
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ForwardingQueue
protected ForwardingQueue()
Constructor for use by subclasses.
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Method Detail
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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 asForwardingSet.delegate()
. Concrete subclasses override this method to supply the instance being decorated.- Specified by:
delegate
in classForwardingCollection<E extends @Nullable Object>
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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 toQueue.add(E)
, which can fail to insert an element only by throwing an exception.
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poll
@CanIgnoreReturnValue @CheckForNull public E poll()
Description copied from interface:java.util.Queue
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.
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remove
@CanIgnoreReturnValue public E remove()
Description copied from interface:java.util.Queue
Retrieves and removes the head of this queue. This method differs frompoll()
only in that it throws an exception if this queue is empty.
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peek
@CheckForNull public E peek()
Description copied from interface:java.util.Queue
Retrieves, but does not remove, the head of this queue, or returnsnull
if this queue is empty.
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element
public E element()
Description copied from interface:java.util.Queue
Retrieves, but does not remove, the head of this queue. This method differs frompeek
only in that it throws an exception if this queue is empty.
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standardOffer
protected boolean standardOffer(E e)
A sensible definition ofoffer(E)
in terms ofForwardingCollection.add(E)
. If you overrideForwardingCollection.add(E)
, you may wish to overrideoffer(E)
to forward to this implementation.- Since:
- 7.0
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standardPeek
@CheckForNull protected E standardPeek()
A sensible definition ofpeek()
in terms ofelement()
. If you overrideelement()
, you may wish to overridepeek()
to forward to this implementation.- Since:
- 7.0
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standardPoll
@CheckForNull protected E standardPoll()
A sensible definition ofpoll()
in terms ofremove()
. If you overrideremove()
, you may wish to overridepoll()
to forward to this implementation.- Since:
- 7.0
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