Verify consistency of method contracts between classes of java

Question

We have a huge application in our company that was bought with its source code (almost all source code actually) and we have been working adapting it to our needs, fixes etc... The way someone a long time ago decided that it would be a good to compile the project was to have the precompiled jars of the original company and only edit or add the classes we needed in an Override folder that we get from some zip files with the original source code. So when we compile we only compile our edited classes, use the original jar in the Classpath and then join our new or edited classes with the original jar to create a new Jar.

The issue seems to be that people are changing method contracts, editing interfaces and adding abstract methods to abstract classes. When we compile we don't recompile the complete source code, only ours so the compiler only checks contract consistency of our Overrided source code. I have started to notice that thing seem to be breaking because old classes are trying to call a method that doesn't exists any more, or classes that call methods of classes that implement what really is just a partial version of the interface.

I cannot that simply join the original source code with our overrided source code because some classes and java files are autogenerated at build time so i could accidentaly fix something that really isnt broken. (I tried, thats why i know)

Is there a way to validate contract consistency between classes of various compiled jars automatically? After fixing those inconcesties i will be able merge both source directories together and avoid this issues in the future.

Answer 1

Why not compile everything? (you do have the source code) That way you will at least get compile errors.

I assume you don't have any tests to verify things still work. Maybe you should start writing those too. A good place to start is to test the new code that is written that has broken before. That way you focus on testing the parts that are changing.