JAVA 1st file for android database

package com.example.database;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    EditText edit1;
    EditText edit2;
    Button but1;
    Button but2;
    Button but3;
    SQLiteDatabase db;
    String nam,coll;


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

        edit1 = (EditText) findViewById(R.id.e1);
        edit2 = (EditText) findViewById(R.id.e2);
        but1 = (Button) findViewById(R.id.bu1);
        but2 = (Button) findViewById(R.id.bu2);
        but3 = (Button) findViewById(R.id.bu3);
        db = openOrCreateDatabase("Mydb",MODE_PRIVATE,null);
        db.execSQL("CREATE TABLE IF NOT EXISTS student(name VARCHAR,college VARCHAR);");

        but1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                nam = edit1.getText().toString();
                coll= edit2.getText().toString();
                db.execSQL("INSERT INTO student VALUES('"+nam+"','"+coll+"');");
                Toast.makeText(getApplicationContext(),"Row Inserted",Toast.LENGTH_SHORT).show();
            }
        });

        but2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                System.exit(0);

            }
        });

        but3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent a = new Intent(MainActivity.this, Database2.class);
                startActivity(a);
                finish();
            }
        });
    }
}