override java final methods via reflection or other means?

Question

This question arise while trying to write test cases. Foo is a class within the framework library which I dont have source access to.

public class Foo{
  public final Object getX(){
  ...
  }
}

my applications will

public class Bar extends Foo{
  public int process(){
    Object value = getX();
    ...
  }
}

The unit test case is unable to initalize as I can't create a Foo object due to other dependencies. The BarTest throws a null pointer as value is null.

public class BarTest extends TestCase{
  public testProcess(){
    Bar bar = new Bar();        
    int result = bar.process();
    ...
  }
}

Is there a way i can use reflection api to set the getX() to non-final? or how should I go about testing?

Answer 1

If your unit test case can't create Foo due to other dependencies, that might be a sign that you're not making your unit test right in the first place.

Unit tests are meant to test under the same circumstances a production code would run, so I'd suggest recreating the same production environment inside your tests. Otherwise, your tests wouldn't be complete.

Answer 2

Seb is correct, and just to ensure that you get an answer to your question, short of doing something in native code (and I am pretty sure that would not work) or modifying the bytecode of the class at runtime, and creating the class that overrides the method at runtime, I cannot see a way to alter the "finalness" of a method. Reflection will not help you here.

Answer 3

you could create another method which you could override in your test:

public class Bar extends Foo {
  protected Object doGetX() {
    return getX();
  }
  public int process(){
    Object value = doGetX();
    ...
  }
}

then, you could override doGetX in BarTest.

Answer 4

If the variable returned by getX() is not final you can use the technique explained in What’s the best way of unit testing private methods? for changing the value of the private variable through Reflection.

Answer 5

public class Bar extends Foo{
  public int process(){
    Object value = getX();
    return process2(value);
  }
  public int process2(Object value){
  ...
  }
}

public class BarTest extends TestCase{
  public testProcess(){
    Bar bar = new Bar();   
    Mockobj mo = new Mockobj();     
    int result = bar.process2(mo);
    ...
  }
}

what i did eventually was the above. it is a bit ugly... James solution is definitely much better than this...