Class FutureTask<V>
- java.lang.Object
-
- java.util.concurrent.FutureTask<V>
- Type Parameters:
-
V
- The result type returned by this FutureTask'sget
methods
- All Implemented Interfaces:
-
Runnable
,Future<V>
,RunnableFuture<V>
public class FutureTask<V> extends Object implements RunnableFuture<V>
A cancellable asynchronous computation. This class provides a base implementation of Future
, with methods to start and cancel a computation, query to see if the computation is complete, and retrieve the result of the computation. The result can only be retrieved when the computation has completed; the get
methods will block if the computation has not yet completed. Once the computation has completed, the computation cannot be restarted or cancelled (unless the computation is invoked using runAndReset()
).
A FutureTask
can be used to wrap a Callable
or Runnable
object. Because FutureTask
implements Runnable
, a FutureTask
can be submitted to an Executor
for execution.
In addition to serving as a standalone class, this class provides protected
functionality that may be useful when creating customized task classes.
- Since:
- 1.5
Constructor Summary
Constructor | Description |
---|---|
FutureTask(Runnable runnable,
V result) | Creates a |
FutureTask(Callable<V> callable) | Creates a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
protected void | done() | Protected method invoked when this task transitions to state |
V | get() | Waits if necessary for the computation to complete, and then retrieves its result. |
V | get(long timeout,
TimeUnit unit) | Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available. |
protected boolean | runAndReset() | Executes the computation without setting its result, and then resets this future to initial state, failing to do so if the computation encounters an exception or is cancelled. |
protected void | set(V v) | Sets the result of this future to the given value unless this future has already been set or has been cancelled. |
protected void | setException(Throwable t) | Causes this future to report an |
String | toString() | Returns a string representation of this FutureTask. |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.concurrent.Future
cancel, isCancelled, isDone
Methods declared in interface java.util.concurrent.RunnableFuture
run
Constructor Detail
FutureTask
public FutureTask(Callable<V> callable)
Creates a FutureTask
that will, upon running, execute the given Callable
.
- Parameters:
-
callable
- the callable task - Throws:
-
NullPointerException
- if the callable is null
FutureTask
public FutureTask(Runnable runnable, V result)
Creates a FutureTask
that will, upon running, execute the given Runnable
, and arrange that get
will return the given result on successful completion.
- Parameters:
-
runnable
- the runnable task -
result
- the result to return on successful completion. If you don't need a particular result, consider using constructions of the form:Future<?> f = new FutureTask<Void>(runnable, null)
- Throws:
-
NullPointerException
- if the runnable is null
Method Detail
get
public V get() throws InterruptedException, ExecutionException
Description copied from interface: Future
Waits if necessary for the computation to complete, and then retrieves its result.
- Specified by:
-
get
in interfaceFuture<V>
- Returns:
- the computed result
- Throws:
-
CancellationException
- if the computation was cancelled -
InterruptedException
- if the current thread was interrupted while waiting -
ExecutionException
- if the computation threw an exception
get
public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
Description copied from interface: Future
Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
- Specified by:
-
get
in interfaceFuture<V>
- Parameters:
-
timeout
- the maximum time to wait -
unit
- the time unit of the timeout argument - Returns:
- the computed result
- Throws:
-
CancellationException
- if the computation was cancelled -
InterruptedException
- if the current thread was interrupted while waiting -
ExecutionException
- if the computation threw an exception -
TimeoutException
- if the wait timed out
done
protected void done()
Protected method invoked when this task transitions to state isDone
(whether normally or via cancellation). The default implementation does nothing. Subclasses may override this method to invoke completion callbacks or perform bookkeeping. Note that you can query status inside the implementation of this method to determine whether this task has been cancelled.
set
protected void set(V v)
Sets the result of this future to the given value unless this future has already been set or has been cancelled.
This method is invoked internally by the RunnableFuture.run()
method upon successful completion of the computation.
- Parameters:
-
v
- the value
setException
protected void setException(Throwable t)
Causes this future to report an ExecutionException
with the given throwable as its cause, unless this future has already been set or has been cancelled.
This method is invoked internally by the RunnableFuture.run()
method upon failure of the computation.
- Parameters:
-
t
- the cause of failure
runAndReset
protected boolean runAndReset()
Executes the computation without setting its result, and then resets this future to initial state, failing to do so if the computation encounters an exception or is cancelled. This is designed for use with tasks that intrinsically execute more than once.
- Returns:
-
true
if successfully run and reset
toString
public String toString()
Returns a string representation of this FutureTask.
- Overrides:
-
toString
in classObject
- Implementation Requirements:
- The default implementation returns a string identifying this FutureTask, as well as its completion state. The state, in brackets, contains one of the strings
"Completed Normally"
,"Completed Exceptionally"
,"Cancelled"
, or"Not completed"
. - Returns:
- a string representation of this FutureTask