DatabaseLogger.java

public class DatabaseLogger implements ILogger {
    @Override
    public void log(String message) {
        //Log to Database here
    }
}

FileLogger.java

public class FileLogger implements ILogger {

    @Override
    public void log(String message) {
        //Log to File here
    }
}

ILogger.java

public interface ILogger {
     void log(String message);
}

MainActivity.java

public class MainActivity extends AppCompatActivity  {

    private ILogger logger = new FileLogger();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        logger.log("onCreate() starts");

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        logger.log("onCreate() ends");
    }
}