How to define an interface throwing a generic exception type?

Question

I wanna define an interface, like

public interface Visitor <ArgType, ResultType, SelfDefinedException> {
     public ResultType visitProgram(Program prog, ArgType arg) throws SelfDefinedException;
     //...
}

during implementation, selfDefinedException varies. (selfDefinedException as a generic undefined for now) Is there a way to do this?

Thanks

You could have your interface be defined to throw an exception that is the superclass of all the selfDefinedExceptions. — Hunter McMillen, Mar 19 '12 at 23:00

score 15 · Accepted Answer · answered Mar 19 '12 at 23:02

15

You just need to constrain the exception type to be suitable to be thrown. For example:

interface Visitor<ArgType, ResultType, ExceptionType extends Throwable> {
    ResultType visitProgram(String prog, ArgType arg) throws ExceptionType;
}

Or perhaps:

interface Visitor<ArgType, ResultType, ExceptionType extends Exception> {
    ResultType visitProgram(String prog, ArgType arg) throws ExceptionType;
}

answered Mar 19 '12 at 23:02

Jon Skeet

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But you'd want to use a conventional naming convention, right? – Tom Hawtin - tackline Mar 19 '12 at 23:19
1

@TomHawtin-tackline: Yes, although the convention in Java for naming type parameters isn't as clear as it is in .NET... – Jon Skeet Mar 20 '12 at 06:45
@JonSkeet I think there are quite clear: single upper case letter (https://docs.oracle.com/javase/tutorial/java/generics/types.html) But it isn't really satisfying so we don't want to follow them :-) – Juh_ Aug 03 '20 at 12:08

score 6 · Answer 2 · answered Mar 19 '12 at 23:01

6

Your genericized parameter would need to extend Throwable. Something like this:

public class Weird<K, V, E extends Throwable> {

   public void someMethod(K k, V v) throws E {
      return;
   }
}

answered Mar 19 '12 at 23:01

Perception

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It's a kind of shame that `E` can't be a set of exception types. – Tom Hawtin - tackline Mar 19 '12 at 23:19
Indeed, that would be a variadic type parameter, which still does not seem to be supported. – Jesse Glick Aug 10 '15 at 17:05

score 1 · Answer 3 · answered Mar 19 '12 at 23:02

You can do something like

public interface Test<T extends Throwable> {
    void test() throws T;
}

And then, for example

public class TestClass implements Test<RuntimeException> {
    @Override
    public void test() throws RuntimeException {
    }
}

Of course, when you instantiate the class you have to declare the exception that is thrown.

EDIT: Of course, replace Throwable with any of your self defined exceptions that will extend Throwable, Exception or similar.

score -4 · Answer 4 · answered Mar 19 '12 at 23:00

-4

If I understand the question, you can throw

Exception

as it is the parent class.

answered Mar 19 '12 at 23:00

kasavbere

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How to define an interface throwing a generic exception type?

4 Answers4