Is there a way to make Runnable's run() throw an exception?

Question

A method I am calling in run() in a class that implements Runnable) is designed to be throwing an exception.

But the Java compiler won't let me do that and suggests that I surround it with try/catch.

The problem is that by surrounding it with a try/catch I make that particular run() useless. I do want to throw that exception.

If I specify throws for run() itself, the compiler complains that Exception is not compatible with throws clause in Runnable.run().

Ordinarily I'm totally fine with not letting run() throw an exception. But I have unique situation in which I must have that functionality.

How to I work around this limitation?

Answer 1

You can use a Callable instead, submitting it to an ExecutorService and waiting for result with FutureTask.isDone() returned by the ExecutorService.submit().

When isDone() returns true you call FutureTask.get(). Now, if your Callable has thrown an Exception then FutureTask.get() wiill throw an Exception too and the original Exception you will be able to access using Exception.getCause().

Answer 2

If you want to pass a class that implements Runnable into the Thread framework, then you have to play by that framework's rules, see Ernest Friedman-Hill's answer why doing it otherwise is a bad idea.

I have a hunch, though, that you want to call run method directly in your code, so your calling code can process the exception.

The answer to this problem is easy. Do not use Runnable interface from Thread library, but instead create your own interface with the modified signature that allows checked exception to be thrown, e.g.

public interface MyRunnable {     void myRun ( ) throws MyException; } 

You may even create an adapter that converts this interface to real Runnable ( by handling checked exception ) suitable for use in Thread framework.