RollNumber.java

package com.darshanbshah.odsystem;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.annotation.MainThread;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;
import java.util.List;

public class RollNumber extends AppCompatActivity implements AdapterView.OnItemSelectedListener{

    private FirebaseAuth mAuth = FirebaseAuth.getInstance();
    private EditText rollNumber;
    private Spinner advisors;

    FirebaseDatabase database = FirebaseDatabase.getInstance();

    DatabaseReference root;
    DatabaseReference student;
    DatabaseReference adv;
    DatabaseReference id;
    DatabaseReference roll_no;
    DatabaseReference email;
    DatabaseReference advisor;

    List<String> list = new ArrayList<String>();
    List<String> lst = new ArrayList<String>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        root = database.getReference();
        student = root.child("Student");
        adv = root.child("Advisors");
        id = student.child(mAuth.getCurrentUser().getUid());
        roll_no = id.child("RollNumber");
        email = id.child("Email");
        advisor = id.child("Advisor");

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_roll_number);
        rollNumber = (EditText)findViewById(R.id.rollNumberEditText);
        advisors = (Spinner)findViewById(R.id.spinner);




        adv.addValueEventListener(new ValueEventListener() {