Whenever we think of creating threads in Java, Runnable interface comes to mind. If we implement Runnable interface, we need to implement run method which takes no arguments and has no return type. But if we expect a value to be returned after completion of a thread, we need to look for something else. Also Runnable can't throw a checked exception.
That something else is Callable. Callable is an interface introduced in Java 5 to meet this requirement. Callable is similar to Runnable, but it returns a value. The call() method is the entry method into a Callable object and it's return type is the type parameter set in the Callable object. Please note that the call() method in Callable object throws a Checked Exception unlike run() method in Runnable which does not throw any exception.
A Future represents the result of an asynchronous computation. The result can be retrieved using get() method when the computation has completed. The call to get() method blocks until the result is computed. Runnable and Callable represent abstract computational tasks. Future represents the life cycle of a task and provides methods to test whether the task has been completed or been cancelled. It can be used to retrieve the result of a task and also cancel the task. If you want to use Future for the sake of cancellability but not provide a usable result, you declare types of the form Future<?> and return null as the result of the underlying task. FutureTask provides a base implementation of Future. You can refer to online Java documentations to know more about Callable, Future and FutureTask.
I have demonstrated the usage of Callable and Future through the following programs :
RandomStringGenerator class :
RandomStringGeneratorTest class :
That something else is Callable. Callable is an interface introduced in Java 5 to meet this requirement. Callable is similar to Runnable, but it returns a value. The call() method is the entry method into a Callable object and it's return type is the type parameter set in the Callable object. Please note that the call() method in Callable object throws a Checked Exception unlike run() method in Runnable which does not throw any exception.
A Future represents the result of an asynchronous computation. The result can be retrieved using get() method when the computation has completed. The call to get() method blocks until the result is computed. Runnable and Callable represent abstract computational tasks. Future represents the life cycle of a task and provides methods to test whether the task has been completed or been cancelled. It can be used to retrieve the result of a task and also cancel the task. If you want to use Future for the sake of cancellability but not provide a usable result, you declare types of the form Future<?> and return null as the result of the underlying task. FutureTask provides a base implementation of Future. You can refer to online Java documentations to know more about Callable, Future and FutureTask.
I have demonstrated the usage of Callable and Future through the following programs :
RandomStringGenerator class :
RandomStringGeneratorTest class :
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