Java Reference
In-Depth Information
Two essential operations are commonly used when dealing with threads: sleep() and join() . Both
operations throw an InterruptedException .
The sleep() method lets the thread sleep for a specii ed period, given in milliseconds. The following
code snippet puts the current thread into the sleep state for one second:
The join() method makes one thread wait for another thread's execution to i nish. Consider a
thread, t1, that needs a resource from another thread, t2. To make t1 wait for t2 to i nish, join t1 to
t2, as shown in the following code snippet:
One of the most well‐known and widely used approaches to programming asynchronously in Java
is using the Future<V> interface. This interface enables the use of a proxy object, which offers a
reference for the future object. Because the concurrency framework does not offer annotation‐
based support for asynchronous execution, the Future interface is mostly coupled with an
ExecutorService , which is part of the concurrency framework.
The following example uses an executor service to complete a task while it returns a reference to the
Future interface with the appropriate generic type:
ExecutorService executor = Executors.newSingleThreadExecutor();
Future<String> reference = executor.submit(
new Callable<String>() {
public String call() {
return "Hello!!";
if (reference.isDone())
The FutureTask class is an implementation of the Future<T> interface, which implements the
runnable interface and can be executed directly:
FutureTask<String> reference = new FutureTask<String>(
new Callable<String>() {
public String call() {
return "Hello!!";
You can cancel this execution by calling the cancel(boolean mayInterruptIfRunning) method.
If the mayInterruptIfRunning  parameter is set to  true , calls to the method  SessionContext
.wasCancelled() return true . Otherwise, a call to the SessionContext.wasCancelled() method
returns  false . To check the status of cancelation, you can use the isCancelled() method, which
returns tru e if a cancelation is successful.
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