Java Exception handling mechanism

Question

Hi,

In Java,If I didn't catch the thrown Exception then the Thread execution stops there else if I catch the same then the Thread execution continues after the catch block.Why Java Exception handling designed in this way.

Thx

Answer 1

The purpose of an exception is to let the program understand that Something Weird Has Happened, and so doing what would ordinarily be next in the program is very likely to be wrong. A function you called couldn't give you a real answer, and you were relying on that answer, so it had to stop you.

There are two ways this can end: you handle the exception (via a catch block), or the entire program stops.

If your program doesn't know what to do when these things happen, it's best to do nothing. Let the Exception crash the thread, and then you can check the crash log later, and find out exactly what crashed the program and why. If your program can't handle an error, the Exception's "crash the thread" behavior lets you see what error was unhandled, so you can change the program to make it able to handle this kind of situation in the future, or prevent the situation from occuring.

Some errors might be pretty normal, though, and shouldn't stop the entire program- you need to have a way to recover from them. That's what a catch block is for: a chance to say "Hello Java, I know just what to do about this problem", and then do it. A Catch block lets you clean up the program and move on, if you can. Java assumes your Catch block deals with the problem and makes it go away. If there's a new problem, or for that matter the same one, you need to throw the caught exception again, or maybe a new one, so something else can try to fix the problem- even if that something else is you, as a programmer.

If exceptions always crashed the program, there would be no way to handle errors that are expected and can be dealt with. But if absolutely nothing is ready to handle the error, the program can't keep running, because now something's gone weird and it doesn't know what to do because you didn't program it to do anything.

Answer 2

In Java,If I didn't catch the thrown Exception then the Thread execution stops there else if I catch the same then the Thread execution continues after the catch block.

There is a third case. If the thread has an Thread.UncaughtExceptionHandler (registered by calling thread.setUncaughtExceptionHandler(handler)), then it will be notified in the event of an uncaught exception on the thread stack ... before the thread exits. (In fact, the behaviour is a bit more complicated than this; see the javadocs.)

Why Java Exception handling designed in this way.

Can you suggest a better way?