Question

This is exceedingly bad OO, but I am not trying to put this in any kind of code that will be used by anyone but the coders themselves — it can never be called except for testing by coders.

Here is the problem I am facing: I have a series of classes that are defined externally. I cannot modify them in any way (except of course I could subclass or call them). They have a variety of names but they do not extend any superclasses (except Object), or implement any interfaces. However what I know about each of them is that they have a method called ‘call’.

For testing, I am trying to write code that will call any one of these classes’ call methods. But, of course, I cannot just say Object.call() because call is not defined for every Object.

Essentially, this will work:

MyClassOne classOne = new MyClassOne();
MyClassOneInput classOneInput = new MyclassOneInput();

classOne.call(classOneInput);

But this will not:

Object clazz = getClassFromElsewhere();
Object clazzInput = getClassInputFromElsewhere();

clazz.call(clazzInput).

Obviously, since Java is a strongly typed language.

BUT, for the sake of 10x faster testing for every person working on this system, can I get around that somehow and somehow use the ‘call’ method for any Class and any ClassInput? I have no problem if it generates an exception or breaks entirely if the wrong classes are passed.

Please help me violate Object Orientation.

Answer 1

You can use reflection to do this.
Check out the reflection API

Here is a simple example:

MyClassOne classOne = new MyClassOne();
MyClassOneInput classOneInput = new MyClassOneInput();
Method m = classOne.getClass().getMethod("call", MyClassOneInput.class);
m.invoke(classOne, classOneInput);

Note: you can use getDeclaredMethod to get any method, including private and protected ones but you’ll need to call “m.setAccessible(true)” on them if they are private/protected.