reg activity

package com.example.myapplication;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import org.json.JSONArray;
import org.json.JSONObject;
import org.json.JSONException;

public class RegisterActivity extends AppCompatActivity {
    private EditText edtUsername, edtPassword;
    private Button btnRegister;

    private void registerUser(String user, String pass) {
        SharedPreferences pref = getSharedPreferences("AppPrefs", MODE_PRIVATE);
        String jsonString = pref.getString("user_list", "[]");

        try {
            JSONArray jsonArray = new JSONArray(jsonString);
            JSONObject newUser = new JSONObject();
            newUser.put("username", user);
            newUser.put("password", pass);

            jsonArray.put(newUser);
            pref.edit().putString("user_list", jsonArray.toString()).apply();
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    protected void onCreate(Bundle saveInstanceState) {
        super.onCreate(saveInstanceState);
        setContentView(R.layout.activity_register);

        edtUsername = findViewById(R.id.editRegUsername);
        edtPassword = findViewById(R.id.editRegPassword);

        btnRegister = findViewById(R.id.regButton2);
        btnRegister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String user = edtUsername.getText().toString().trim();
                String pass = edtPassword.getText().toString().trim();

                if (user.isEmpty() || pass.isEmpty()) {
                    Toast.makeText(RegisterActivity.this, "Please enter all the information!", Toast.LENGTH_SHORT).show();
                    return;
                }

                registerUser(user, pass);

                Toast.makeText(RegisterActivity.this, "Register success !", Toast.LENGTH_SHORT).show();
                finish();
            }
        });
    }
}