Package com.google.common.collect

Class ForwardingQueue<E>

  • All Implemented Interfaces:
    Iterable<E>, Collection<E>, Queue<E>
    Direct Known Subclasses:
    EvictingQueue, ForwardingBlockingQueue, ForwardingDeque
    @GwtCompatible
public abstract class ForwardingQueue<E>
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 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>

      • 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>
        Parameters:
        o - the element to add
        Returns:
        true if the element was added to this queue, else false

      • poll

        @CanIgnoreReturnValue
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>
        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>
        Returns:
        the head of this queue

      • peek

        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>
        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>
        Returns:
        the head of this queue