How do I use custom exception in Java? I've followed the steps but am not getting my catch clauses to work

I've been spending hours trying to figure out what's wrong with my java exception handling. I've followed all the books and sites in creating customs exceptions, throwing them, and attempting to catch them. They're extending RuntimeException (because they're thrown in an ActionEvent) so I don't think the throws clause needs to be declared in the method header. But the catch clauses won't run. Here's the pertinent code:

public void handle(ActionEvent event){
Object selectedButton = event.getSource();
if (selectedButton == b1)
{
String passwordStr1 = password1.getText();
String passwordStr2 = password2.getText();

if(passwordStr1.equals(passwordStr2))


if(PasswordCheckerUtility.isValidPassword(passwordStr1)== true)

Alert validAlert = new Alert(AlertType.INFORMATION);
validAlert.setTitle("Password Status");
validAlert.setHeaderText("Password is valid");
validAlert.showAndWait();



else
try

throw new UnmatchedException("The passwords do not match");

catch(UnmatchedException ue)
Alert unEAlert = new Alert(AlertType.ERROR);
unEAlert.setTitle("Password Status");
unEAlert.setContentText(ue.getMessage());





and

public class UnmatchedException extends RuntimeException

public UnmatchedException(String message)

super(message);





unEAlert.showAndWait()

that's exactly right

2 Answers
2

I tried a more basic example and it seemed to work. Perhaps the issue is with some other aspect of your code. Here's what I used:

A main method:

public static void main(String...args)
handle(null);
//main()


The handle method:

public static void handle(ActionEvent event)
try
throw new UnmatchedException("The passwords do not match");
catch(UnmatchedException ue)
System.out.println(ue.getMessage());




And the custom exception in a separate class:

public class UnmatchedException extends RuntimeException
private static final long serialVersionUID = 1L;

public UnmatchedException(String message)

super(message);




Not really sure why you would throw/catch the Exception in the same method.

Exception processing is relatively expensive and should be avoided if possible. In your simple example you are just attempting to display an Alert message. That could easily be done in the "else statement".

I would typically only throw the Exception when you want the code that invoked the method to handle the Exception.

In any case throwing and catching the Exception in the same method works fine for me:

public class ExceptionTest

public static void main(String args)

validate("hello there");
validate("bye");


public static void validate(String text)

if (text.length() > 7)
System.out.println("everythings good");
else

try

if (text.length() < 8)
throw new StringTooShortException("Must be at least 8 characters");

catch (StringTooShortException e)

System.out.println(e);




static class StringTooShortException extends RuntimeException

public StringTooShortException(String message)

super(message);





When learning a new concept it is easier to start with simple code and get it working and then apply the knowledge to your real application. This problem is likely caused by your validation logic.

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