Caused by: java.lang.IllegalStateException: Call `Realm.init(Context)` before calling this method.

        at io.realm.Realm.getDefaultInstance(Realm.java:402)

        at com.example.imoocmusicdemo.helps.RealmHelper.<init>(RealmHelper.java:29)

        at com.example.imoocmusicdemo.activities.MainActivity.initData(MainActivity.java:38)

        at com.example.imoocmusicdemo.activities.MainActivity.onCreate(MainActivity.java:33)