Exception handling help (newbie)

[DHS1]

Hey guys. I have a lab that is due in two weeks, but I wanted to start on it now. Problem is, I'm at home during christmas break so I can't ask my professors. Here's my problem:

I am given a very fragile program and I have to add the exception handling and error checking and pretty much make it uncrashable.

I will show just one small step in this lab. If you can answer it, I think I'll be able to do the rest. I just need to get headed in the right direction because my Java book and online tutorials aren't helping.

I need to do what the TODO says. This is a Constructor method. The length it's talking about has to be 10. Here's the code:

	public DateStringConverter(String startDate, String endDate ){
//TODO make sure that both text fields contain text; generate an Exception if NULL strings or invalid length;
//TODO In the Exception, specify the reason: exactly which field (Start or End Date) contained the error.
		
		parseDateStrings( startDate, endDate );
	}

I'm then supposed to catch the exceptions (that I made in that constructor) in this code (remember Im just showing a small secion)

// prompt for input
		String startDate = JOptionPane.showInputDialog("Enter a start date as mm/dd/yyyy.");
		String endDate = JOptionPane.showInputDialog("Enter an end date as mm/dd/yyyy");

		//TODO catch Exceptions thrown from within DateStringConverter; report errors on exceptions,
		//TODO report EXACTLY the cause of the error in a message dialog, and loop to repeat the previous prompts
		DateStringConverter dsc = new DateStringConverter(startDate, endDate);

I tried putting exception handling in the constructor method I showed you earlier, and this is what it looked like:

	public DateStringConverter(String startDate, String endDate ) throws Exception{
//TODO make sure that both text fields contain text; generate an Exception if NULL strings or invalid length;
//TODO In the Exception, specify the reason: exactly which field (Start or End Date) contained the error.
		if((startDate==null)||(startDate.length()>10||startDate.length()<10)){
			Exception start = new Exception("If start date is null or too short/long");
			throw start;
		}
		if((endDate==null)||(endDate.length()>10||endDate.length()<10)){
			Exception end = new Exception("If end date is null or too short/long");
			throw end;
		}
		parseDateStrings( startDate, endDate );

But when I went to the main method (second block of code I showed you) I couldn't figure out how to catch the exception named "start" that I threw.

So can anyone tell me how I could do this? The TODO:'s in the code are what I need to do in case you didn't read this whole thing. Thanks, and let me know if you need to see more of the code.

[Twey]

A method that throws an exception of type SomeException looks like this:

void someMethod() throws SomeException {
    throw new SomeException();
}

And to catch that exception, one would do:

try {
    someMethod();
} catch (SomeException e) {
    // Handle the exception (which object is available as 'e')
}

The types are specified because you can throw and handle multiple types of exception at once:

void someMethod() throws SomeException, SomeOtherException {
    throw someCondition ? new SomeException() : new SomeOtherException();
}

try {
    someMethod();
} catch (SomeException e) {
    // handle a SomeException
} catch (SomeOtherException e) {
    // handle a SomeOtherException
}