应用程序类返回nullpointer

Question

我的AplicationClass ==＆gt;

Date

当从其他类调用internetAktif函数时==＆gt;

@Override
public void onCreate() {
    super.onCreate();
    mydRef = FirebaseDatabase.getInstance().getReference();
    tipDondur();
}

public static Context context() {
    return app.getApplicationContext();
}

public boolean internetAktif() {
    final ConnectivityManager connectivityManager = ((ConnectivityManager) app
            .getApplicationContext()
            .getSystemService(Context.CONNECTIVITY_SERVICE));
    return connectivityManager.getActiveNetworkInfo() != null &&
            connectivityManager.getActiveNetworkInfo().isConnected();
}

发送错误==＆gt;

引起：com.example.ercana.yemekevdefb.App.internetAktif（App.java:38）中的java.lang.NullPointerException：com.example.ercana.yemekevdefb.Splash.onCreate（Splash.java:31）< / p> 这是什么意思？我是如何解决这个问题的？