This class is a Runnable wrapper around a Callable object (or around another Runnable). FutureTask is a generic type and the type variable V represents the return type of the wrapped Callable object. AbstractExecutorService uses FutureTask to convert Callable objects passed to the submit( ) method into Runnable objects it can pass to the execute( ) method.

FutureTask also implements the Future interface, which means that the get( ) method waits for the run( ) method to complete and provides access to the result (or exception) of the Callable's execution.

The protected methods set( ) and setException( ) are invoked when the Callable returns a value or throws an exception. done( ) is invoked when the Callable completes or is canceled. Subclasses can override any of these methods to insert hooks for notification, logging, and so on.

Figure 16-85. java.util.concurrent.FutureTask<V>

public class FutureTask<V> implements Future<V>, Runnable {
// Public Constructors
     public FutureTask(Callable<V> callable);  
     public FutureTask(Runnable runnable, V result);  
// Methods Implementing Future
     public boolean cancel(boolean mayInterruptIfRunning);  
     public V get( ) throws InterruptedException, ExecutionException;  
     public V get(long timeout, TimeUnit unit) throws InterruptedException, 
        ExecutionException, TimeoutException;  
     public boolean isCancelled( );  
     public boolean isDone( );  
// Methods Implementing Runnable
     public void run( );  
// Protected Instance Methods
     protected void done( );                                              empty
     protected boolean runAndReset( );  
     protected void set(V v);  
     protected void setException(Throwable t);  
}