mainactivity and error

package com.example.mysqlexampleproject;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.content.Intent;
import android.content.res.Resources;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Adapter;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;

import org.json.JSONArray;

import java.sql.Array;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

public class MainActivity extends AppCompatActivity {

        //googleBtn.setOnClickListener(new View.OnClickListener() {
//
  //          @Override
    //        public void onClick(View v) {
      //          //String google = "https://www.google.com";
        //        //Uri webaddress = Uri.parse(google);

                //Intent gotoGoogle = new Intent(Intent.ACTION_VIEW, webaddress);
                //if (gotoGoogle.resolveActivity(getPackageManager()) != null) {
                //    startActivity(gotoGoogle);
                //}
   //         }
    //    });

    //}

    ArrayAdapter ArrayAdapter;
    // Construct the data source
    ArrayList<user> arrayOfUsers = new ArrayList<user>();
    // Create the adapter to convert the array to views
    UsersAdapter adapter = new UsersAdapter(this, arrayOfUsers);
    // Attach the adapter to a ListView
    ListView listView = (ListView) findViewById(R.id.myListView);
    //listView.setAdapter(ArrayAdapter);
    Context thisContext;
    ListView myListView;
    TextView progressTextView;
    Integer resource;
    //Map<Integer, String> usersMap = new LinkedHashMap<Integer, String>(); //A Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value.
    //String[][] userList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Attempts to launch an activity within our own app
        //Button secondActivityBtn = (Button)findViewById(R.id.loginBtn);
        //secondActivityBtn.setOnClickListener(new View.OnClickListener() {

        //    @Override
        //    public void onClick(View v_) {
        //        Intent startIntent = new Intent(getApplicationContext(), loginScreen.class);
        //        //show how to pass info to another activity
        //        startIntent.putExtra("com.example.mysqlexampleproject.NAME", "TEST");
        //        startActivity(startIntent);
        //    }
        //});

        //Attempt to launch an activity outside our app
        //Button googleBtn = (Button)findViewById(R.id.signUpBtn);

        Resources res = getResources();
        myListView = (ListView) findViewById(R.id.myListView);
        progressTextView = (TextView) findViewById(R.id.progressTextView);
        thisContext = this;
        listView.setAdapter(adapter);

        progressTextView.setText("");
        Button btn = (Button) findViewById(R.id.getDataButton);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                GetData retrieveData = new GetData();
                retrieveData.execute("");
            }
        });
    }

    private class GetData extends AsyncTask<String,String,String> {

        Integer flag = 0;
        //Integer user = 0;
        String msg = "";
        //JDBC driver name and database URL
        static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        // Example: 10.20.30.40:3306
        static final String DB_URL = "jdbc:mysql://" + DBStrings.DATABASE_URL + "/" + DBStrings.DATABASE_NAME;

        @Override
        protected void onPreExecute() {
            progressTextView.setText("Connecting to database...");
        }

        @Override
        protected String doInBackground(String... params) {

            Connection conn = null;
            Statement stmt = null;

            try {

                flag = 1;
                Class.forName(JDBC_DRIVER);
                conn = DriverManager.getConnection(DB_URL, DBStrings.USERNAME, DBStrings.PASSWORD);
                //conn = DriverManager.getConnection(DB_URL);

                flag = 2;
                stmt = conn.createStatement();
                String sql = "SELECT * FROM users";
                ResultSet rs = stmt.executeQuery(sql);

                //lets hope this works
                ArrayList<user> users = new ArrayList<>();

                /*
                // Add item to adapter
                User newUser = new User("Nathan", "San Diego");
                adapter.add(newUser);
// Or even append an entire new collection
// Fetching some data, data has now returned
// If data was JSON, convert to ArrayList of User objects.
                JSONArray jsonArray = ...;
                ArrayList<User> newUsers = User.fromJson(jsonArray)
                adapter.addAll(newUsers);
                */


                flag = 3;
                while (rs.next()) {
                    Integer userID = rs.getInt("userID");
                    String firstName = rs.getString("firstName");
                    String surname = rs.getString("surname");
                    String username = rs.getString("username");
                    user newUser = new user(username, userID);
                    newUser.user_id = userID;
                    newUser.username = username;
                    //UsersAdapter.add(newUser);
                    adapter.add(newUser);
                    //Double price = rs.getDouble("price");
                    //userList[user][0] = firstName;
                    //userList[user][1] = surname;
                    //userList[user][2] = username;
                    //usersMap.put(userID, firstName);
                    //usersMap.put(name, price);
                    //user += 1;
                    flag = 4;
                }

                msg = "Process complete.";

                rs.close();
                stmt.close();
                conn.close();


                //milbs recommends you create static array list of users in user class (or new class)
                //ArrayList<user> users = new ArrayList<>();
                //user newUser = new user();
                //newUser.user_id = 5;
                //newUser.username = "TJM4";
                //users.add(newUser);

                //users.contains(newUser);


                //milbs recommends you dont use these
                //HashMap<String, user> newHashmap = new HashMap<>();
                //newHashmap.put("new user string", newUser);

                //user userfromhashmap = newHashmap.get("new user string");



            } catch (SQLException connError) {
                msg = "An exception was thrown for JDBC.\nFlag: " + flag.toString();
                connError.printStackTrace();
            } catch (ClassNotFoundException e) {
                msg = "A class not found exception was thrown.";
                e.printStackTrace();
            } finally {

                try {
                    if (stmt != null) {
                        stmt.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }

                try {
                    if (conn != null) {
                        conn.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }

            }

            return null;
        }

        @Override
        protected void onPostExecute(String msg) {

            progressTextView.setText(this.msg);

            //if (userList.length() > 0) {
              //  itemAdapter = new ItemAdapter(thisContext, userList);
                //myListView.setAdapter(itemAdapter);
            //}

            //if (usersMap.size() > 0) {
            if (arrayOfUsers.size() > 0) {

                //itemAdapter = new ItemAdapter(thisContext, usersMap);
                ArrayAdapter = new ArrayAdapter(thisContext, resource);
                myListView.setAdapter(ArrayAdapter);
            }
        }
    }

} //END OF MAINACTIVITY

//////ERROR//////
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mysqlexampleproject, PID: 7036
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.mysqlexampleproject/com.example.mysqlexampleproject.MainActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
        at android.app.Activity.getSystemService(Activity.java:5915)
        at android.view.LayoutInflater.from(LayoutInflater.java:229)
        at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:210)
        at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:204)
        at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:190)
        at com.example.mysqlexampleproject.UsersAdapter.<init>(UsersAdapter.java:18)
        at com.example.mysqlexampleproject.MainActivity.<init>(MainActivity.java:52)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1174)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2669)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Process 7036 terminated.