Exception Handling in JApplet

[cantene]

I wish to ask one more question on Java. I want to implment some error
handling mechanisms in my assignment. Say if the result of calculation is too
long
to display within 8 digits, I would like to throw a self-defined exception for
the
error handler to catch it and display the corresponding message.

My code structure is like:

import java.*;
public class BinaryCalculator extends JApplet implements ActionListener {

   :
   :
   public void init() {...}

   public void actionPerformed(ActionEvent e) throws BinaryCalculatorException
{
      try { ... 
         if certain_condition then throw new Overflow();
      }
      catch (BinaryCalculatorException err) {
         if (err instanceof Overflow) {
	    System.out.println("Overflow");
	 }
      }
   }
}

class BinaryCalculatorException extends Exception {};
	
class Overflow extends BinaryCalculatorException {};

When I compile the program, the following message shows in the command prompt:

BinaryCalculator.java:19: actionPerformed(java.awt.event.ActionEvent) in
BinaryC
alculator cannot implement actionPerformed(java.awt.event.ActionEvent) in
java.a
wt.event.ActionListener; overridden method does not throw
BinaryCalculatorExcept
ion
public class BinaryCalculator extends JApplet implements ActionListener {
^
1 error

I can't root this out unless I remove the "throws
BinaryCalculatorException"
statement. This is just to declare what exceptions this method can thow. So why

not I can't write this down? What's wrong with throwing exception in overridden

method and how should I tackle this?

Thank you for your kind attention.

You do one of two things in exception handling:
Either declare that it throws your (Custom) Exception(s) (which you cannot do when extending a class that doesn't already throw this exception or parent exception)
or use a try/catch block.
So in your case, remove the "throws BinaryCalculatorException" part.

I asume you know this: Beyond the above, you need to remove ":", "...", import appropriate classes and instantiate your class to get to the "System.out.println("Overflow");" part.