How do I catch and recover from a stack overflow in Java?

Question

I am writing a grading program for an assignment in which students are implementing recursive sort algorithms. This means several students will probably turn in broken code which causes stack overflow. I would like to somehow catch stack overflows that occur when calling the students code so I can deduct from their score and continue on to other tests. Unfortunately, stack overflow doesn't seem to go through the standard path of other exceptions - try/catch blocks don't seem to help. Is there a way to return execution to my code after a stack overflow has occurred? I've looked into using threads to do this, but it just seems to come back to not being able to use try/catch.

Answer 1

When calling the methods of your students, you should embed the calls in try-catch blocks and catch Exceptions as Throwables.

See the following code:

public class Test {
    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            soe();
        } catch (Throwable e) {
            System.out.println("Caught:" + e
                    + ", everything went better than expected.");
        }
    }
    /**
     * Method producing StackOverflowError
     */
    public static void soe() {
        soe();
    }
}

More info

When catching Throwables you will catch:

• Normal Exceptions - which enforce you to use try-catch or throws (eg. IOException)
• RuntimeExceptions - which bubble up through methods (eg. NullPointerException)
• Errors - eg. StackOverflowError

See the official Java Docs on the Throwable object

Answer 2

You could fire off their programs using a new Process and then redirecting its error stream to check for stack overflow.