Define Implementation for abstract Object

Question

I am looking for a way to do the following:

A Project : Defines an abstract class that is called when some events happen (event handler if you will) Defines the engine that will fire the events using the event handler above

B Project: Defines the implementation for the abstract class Runs the engine.

How can i register the implementation class and make sure that is the one being called when the engine runs.

EDIT 1: By register i mean i must somehow define which is the implementation that should be called for that given abstract object

Sorry if the question isn't too clear, let me know if you need some more details

As far as I understand (maybe you can give some more clarification e.g. Pesudo Code) you would have to instantiate the actual B Project implementation as a reference to the A Project abstract class. — Daff, Jul 27 '09 at 12:15

score 2 · Answer 1 · edited Jul 27 '09 at 14:26

2

Something like this?

class A implements EventHandlerForB {
...
}

public class B {
  private EventHandlerForB eventHandler;

  public void registerEventHandler(EventHandlerForB eventHandler) {
    this.eventHandler = eventHandler;
  }
...
}

public interface EventHandlerForB {
...
}

edited Jul 27 '09 at 14:26

Tom Hawtin - tackline

145,806
30
211
305

answered Jul 27 '09 at 12:19

palindrom

18,033
1
21
37

Passing it thought the constructor is probably better for unicast. – Tom Hawtin - tackline Jul 27 '09 at 14:24
This solution did require me to code the class that invokes the handler, which i am not doing. using your objects, in my problem class B would be closed and class A would be what i implement. – Nuno Furtado Jul 27 '09 at 17:35

score 1 · Accepted Answer · answered Jul 27 '09 at 14:57

1

At runtime, you can have the name of the implementation passed in your A project (with a properties file or a Java system property). Then you find this class in the classpath with class.forName() and instantiate it with newInstance().

But you'd prefer using a framework like Guice or Spring, that will allow you to glue stuff together in a clean way.

answered Jul 27 '09 at 14:57

fg.

331
1
3
6

The solution i implemented is based on your first sugestion, i had a look at Guice and may end up going for it, but for now this is enough thx – Nuno Furtado Jul 28 '09 at 17:12

score 0 · Answer 3 · answered Jul 27 '09 at 12:21

0

there are several "patterns" that try to address this issue. Using only JDK (6 or above) classes you may want to take a look at java.util.ServiceLoader

answered Jul 27 '09 at 12:21

dfa

114,442
31
189
228

Define Implementation for abstract Object

3 Answers3

Linked