Class ForwardingListenableFuture<V>

  extended by
      extended by<V>
          extended by<V>
Type Parameters:
V - The result type returned by this Future's get method
All Implemented Interfaces:
ListenableFuture<V>, Future<V>
Direct Known Subclasses:
ForwardingCheckedFuture, ForwardingListenableFuture.SimpleForwardingListenableFuture

public abstract class ForwardingListenableFuture<V>
extends ForwardingFuture<V>
implements ListenableFuture<V>

A ForwardingListenableFuture.SimpleForwardingListenableFuture which forwards all its method calls to another future. Subclasses should override one or more methods to modify the behavior of the backing future as desired per the decorator pattern.

Most subclasses can just use ForwardingListenableFuture.SimpleForwardingListenableFuture.

Shardul Deo

Nested Class Summary
static class ForwardingListenableFuture.SimpleForwardingListenableFuture<V>
          A simplified version of ForwardingListenableFuture where subclasses can pass in an already constructed ListenableFuture as the delegate.
Nested classes/interfaces inherited from class
Constructor Summary
protected ForwardingListenableFuture()
          Constructor for use by subclasses.
Method Summary
 void addListener(Runnable listener, Executor exec)
          Registers a listener to be run on the given executor.
protected abstract  ListenableFuture<V> delegate()
          Returns the backing delegate instance that methods are forwarded to.
Methods inherited from class
cancel, get, get, isCancelled, isDone
Methods inherited from class
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.concurrent.Future
cancel, get, get, isCancelled, isDone

Constructor Detail


protected ForwardingListenableFuture()
Constructor for use by subclasses.

Method Detail


protected abstract ListenableFuture<V> 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 ForwardingFuture<V>


public void addListener(Runnable listener,
                        Executor exec)
Description copied from interface: ListenableFuture
Registers a listener to be run on the given executor. The listener will run when the Future's computation is complete or, if the computation is already complete, immediately.

There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called once the computation is complete.

Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException or an exception thrown by inline execution) will be caught and logged.

Note: For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.sameThreadExecutor(). For heavier listeners, sameThreadExecutor() carries some caveats: First, the thread that the listener runs in depends on whether the Future is done at the time it is added and on whether it is ever canclled. In particular, listeners may run in the thread that calls addListener or the thread that calls cancel. Second, listeners may run in an internal thread of the system responsible for the input Future, such as an RPC network thread. Finally, during the execution of a sameThreadExecutor() listener, all other registered but unexecuted listeners are prevented from running, even if those listeners are to run in other executors.

This is the most general listener interface. For common operations performed using listeners, see Futures

Specified by:
addListener in interface ListenableFuture<V>
listener - the listener to run when the computation is complete
exec - the executor to run the listener in

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