Gradle (Java) cannot find symbol for class in subdirectory of package

It’s been some years since I have programmed Java and I am having trouble with resolving a build issue with not finding a symbol for a class in the same package directory structure.

package com.A.B.C; 
public class Manager {
...
}

The following class is attempting to reference Manager. Note the package declarations for both classes.

package com.A.B;
import com.A.B.C.Manager; // I have also tried omitting this import statement; same result 
public class MyApp extends Application {                                                               
...
  @Override                                                                                            
  public void onCreate() {
...
    registerActivityLifecycleCallbacks(Manager); // cannot find symbol SessionManager
  }
...
}

I am importing com.A.B.C.Manager in other source files and able to reference Manager there but, for this source file, Gradle cannot resolve the symbol.

What am I missing? (This is an Android project by the way, in case that is relevant.)

In advance, thank you.

Answer

That Manager class have to implement Application.ActivityLifecycleCallbacks like this:

package com.A.B.C; 
public class Manager implements Application.ActivityLifecycleCallbacks{
    ...
}  

Also, I guess you missed the new while calling registerActivityLifecycleCallbacks() :

registerActivityLifecycleCallbacks(new Manager());