Why does this demo implement DJISDKManager.SDKManagerCallback twice in ConnectionActivity.java and DemoApplication.java?

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[timelikeswind]

ConnectionActivity.java

public class ConnectionActivity extends Activity implements View.OnClickListener {
    private void startSDKRegistration() {
        DJISDKManager.getInstance().registerApp(getApplicationContext(), new DJISDKManager.SDKManagerCallback() {
        }
    }
}

DemoApplication.java

public class DemoApplication extends Application {
    @Override
    public void onCreate() {
        DJISDKManager.SDKManagerCallback mDJISDKManagerCallback = new DJISDKManager.SDKManagerCallback() {
        }
    }
}