Calling a class not included in your application package

Hi all,

I hope I can explain this clearly and that someone can assist me with this issue.

I have an application that needs to call a class from a dependant application.   However, I need to alleviate the need of having the dependant code included in the applications release package, yet still compile as though it were there.

I was instructed to create an interface for the class that I will be dependant on, and have that class implement the interface of my application.  Then store the class name in a property file and use that property to instantiate the class name in my code and call the necessary methods at that time.

So, there are two problems I have.  One, is the interface design.  The dependant package has relatively simple public methods, but there is one method that is dependant on another class in that package. i.e., the dependant classes are similar to this:

class Test1 {
 public void addMethod() {
  // they have code here
 }

 public void testMethod () {
  //they have code here
 }

 public void exampleMethod () {
   //again code here
 }

 public Test2 createMethod () {
  //code here that uses another class
}
}

class Test2 {
 Test2 () { //constructor which I call }
 //additional code
}

Now I'm supposed to create an interface for Test1 for the exampleMethod and the createMethod...but like I said the createMethod references another class.  Do I need to create an interface for the Test2 class?  How do I do that, if you can't put constructors in interfaces?

Then in my code, I need to reference my interfaces and instantiate the Test1 class via the classname defined in the properties file, then call the methods defined in the interface:

//get property value
//instantiate the object
Test1 test1 = new Test1();
test1.exampleMethod();
Test2 test2 = test1.createMethod();

Hopefully that made sense!  Can anyone help me using the example above to show me how the code would look and work correctly?

Thanks