Throwing two exceptions from a method

[ven jovovich]

Hi all,
Please refer to the below code. I am not getting what happens to "exception 1". Seems that the JVM eats up the exception.

import java.io.*;
import java.awt.AWTException;

class C {
	void meth() throws IOException, AWTException {
		try {
			throw new ArrayIndexOutOfBoundsException();
		} catch (ArrayIndexOutOfBoundsException e) {
			System.out.println("array index exception caught");
			throw new Exception(); //exception 1
		} finally {
			System.out.println("in finally");
			throw new AWTException("my AWT ex"); //exception 2
		}
	}
}

class B {
	void methB() {
		try {
			new C().meth();
		} catch (Throwable e) {
			e.printStackTrace();
		}
	}
}

class A {
	public static void main(String[] args) {
		System.out.println("main starts");
		new B().methB();
		System.out.println("main ends");
	}
}

output:

main starts
array index exception caught
in finally
java.awt.AWTException: my AWT ex
        at C.meth(A.java:13)
        at B.methB(A.java:21)
        at A.main(A.java:31)
main ends

I expected the JVM to crash since B.methB() can handle only one exception.
Please help.

Regards,
Ven.

[Campbell Ritchie]

Consider that a finally specifies something which is happens whether or not an Exception is thrown in its preceding try. What you are saying is something like

Whether or not an Exception occurs in the try, I want an AWTException.

So the AWT Exception hides the original Exception. This is normal. You can’t have two Exceptions simultaneously in the same thread. The compiler can tell that if it allows that code to compile without your declaring the Exception.
If you go through the Java Tutorials section, you find you can chain Exceptions together if you want several Exceptions.

[Steve Luke]

The JVM doesn't eat the exception, your code hides it. Only one exception can be thrown from a method. The finally clause will execute regardless of what happens in the try or catch clause. So if the try throws an exception, the finally gets called anyways. Then the finally clause causes an exception. Since the finally clause was called after the try's exception was thrown its exception takes precedence and is thrown to the caller.

You should never do this. Do not let exceptions escaped a finally clause.

[Henry Wong]

ven jovovich wrote:
I expected the JVM to crash since B.methB() can handle only one exception.
Please help.

And did you really expect the JVM to crash? If it was that easy to crash a JVM, you will wind up with very unstable web and app servers.

Henry

[ven jovovich]

Thanks Campbell, Steve and Henry.
Henry, by "crash" I meant that the JVM would spit out the unhandled exception and exit.
BTW, what happens to the

new Exception() 

object created on line 10? Is it just GCed?

Regards,
Ven.

[Winston Gutkowski]

ven jovovich wrote:Is it just GCed?

I imagine so. After all, there aren't any outside references to it.

Winston

[ven jovovich]

Thanks Winston.