How to solve build error for product flavor, when a referenced but unnecessary source/resource not found?

Question

I have a project and it has 2 product flavors with their own directories:

build.gradle:

android {
    ...
    productFlavors {
            free {
                applicationId "com.sample.free"
                 buildConfigField "boolean", "free", "true"
            }
            paid {
                applicationId "com.sample"
                buildConfigField "boolean", "free", "false"
            }
    }
}

And I have a class (such as PaidOperationClass) which is only used at paid flavor. So, I put that class under src/paid/java directory. And I have another class(such as CommonClass) which is used by both flavors. So I put that under src/main/java directory:

src/main/  --> has CommonClass
src/free/
src/paid/  --> has PaidOperationClass

In CommonClass I have a method such as:

if(!BuildConfig.FREE) {
    PaidOperationClass.doSomeStuff();
}

So the PaidOperationClass is referenced(has an import) but never used by free build.

If I build the application for paid flavor everything works perfect. But if I try to build it for free flavor, it fails because referenced but unnecessary class is not found. How do you solve this without code (class/method) replication (such as putting a dummy PaidOperationClass under free flavor)? Are there any gradle options which ignores this kind of build errors while building?

Edit: I need a gradle solution which won't need code replication. An annotation based custom script maybe, which removes unnecessary code for product flavors at compile time.

Answer 1

You can't do it, because the import statement is inside the CommonClass and it is not able to resolve PaidOperationClass in the free flavor.

One way to achieve it is:

Create an empty class in Free flavor:

public class PaidOperationClass{

  public static void doSomeStuff(){
      //do nothing..    
  }
}

Answer 2

The easiest solution might be to create a class: IPaidOperations that is housed in the /src/main directory that the PaidOperationClass implements. Then just use the interface in the CommonClass.