Creating an Exception for a method

Question

Hello I'm still new to programming and I have recently learned about Exceptions and how it is better to Define a exception than use a generic one. I have researched and I understand the basic idea of Creating exceptions such as using String and Throwable. However when it come to code like this:

public void sendEnvironmentExport(Environment env) throws Exception {

    if (details == null) {
        details = new CurrentUserDetails();
        details.setPrincipal(dao.loadUser(UserServiceImpl.SYSTEM_USERNAME));
    }

    for (String reportDescriptor : env.getExportReports()) {
        // methodName|recipient@address.com
        String[] parts = reportDescriptor.split("\\|");

        if (parts.length == 2) {
            Method m = this.getClass().getMethod(parts[0], String.class);
            m.invoke(this, parts[1]);
        } else {
            logger.warn("Ignoring invalid Environment.getExportReports.report: " + reportDescriptor);
        }
    }

}

I have no clue where to begin with creating and exception. So basically my question is. In these cases is it better to Define and exception or use a generic one?

Sorry if I am asking an unclear question I am simply trying to understand if there is any need to define an exception for methods such as this where there is no clear area if the exception being thrown.

That depends, where you want to break the execution of the method in case of unexpected occurence and why? — Marcos Vasconcelos, Mar 07 '18 at 14:07
Please edit for formatting, typos and clarity. I don't really know what you are asking? — Jan Larsen, Mar 07 '18 at 14:08

score 1 · Accepted Answer · answered Mar 07 '18 at 14:11

In most situations it's nicer to use a specific exception that extends from the closest possible generic exception, unless there is a predefined Java exception that gives exactly the information you would want to give. The reason for using a custom one is that the exception can be handled in a very specific manner. Even if a method can throw multiple similar but still distinct custom exceptions, one can easily handle each one individually or all at once (by handling the superclass exception).

score 0 · Answer 2 · answered Mar 07 '18 at 14:15

0

There are a number of different strategies for handling exceptions. Some developers use only RuntimeExceptions, some developers use only standard exceptions, some developers define a few general exceptions, say one per tier, and others define exceptions for every possible error. It is really a question of preference and stile.

An exception can be created like this:

public class MyException extends RuntimeException{
    private static final long serialVersionUID = 1L;
}

It can be thrown like this:

throw new MyException();

and cought like this:

try {
    throw new MyException();
} catch (MyException e) {
    e.printStackTrace();
}

answered Mar 07 '18 at 14:15

Jan Larsen

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Be careful when you create an Exception which extends `RuntimeException` since this is a [Unchecked Exception](https://docs.oracle.com/javase/tutorial/essential/exceptions/runtime.html) – Mar 07 '18 at 14:20
Yes, RuntimeException is a special case and probably not the best example – Andreas Hartmann Mar 07 '18 at 14:21
That was very deliberate. I think checked exceptions were a mistake. They cause way more confusion and bad code than they cause good. Discussion here: https://stackoverflow.com/questions/613954/the-case-against-checked-exceptions – Jan Larsen Mar 07 '18 at 14:47

Creating an Exception for a method

2 Answers2