public class Settings extends AppCompatActivity {

    private static final String TAG = "SettingsActivity";
    private RelativeLayout layout;
    private SharedPreferences preferences;
    private Bundle savedInstanceState;

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

        assert getSupportActionBar() != null;
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        Spinner spinner = findViewById(DarkMode);

        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                Log.e(TAG, "onItemSelected: " + position);
                handleNightMode(position);
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
                Log.e(TAG, "onNothingSelected: ");
            }
        });

    }

    private void handleNightMode(int position) {

        switch (position) {
            case 0:
                Log.e(TAG, "Nothing Selected");
                break;
            case 1:
                Log.e(TAG, "FOLLLOW_SYSTEM");
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
                getDelegate().applyDayNight();
                break;
            case 2:
                Log.e(TAG, "YES");
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
                getDelegate().applyDayNight();
                break;
            case 3:
                Log.e(TAG, "NO");
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);
                getDelegate().applyDayNight();
                break;
            case 4:
                Log.e(TAG, "AUTO");
                AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_AUTO_BATTERY);
                getDelegate().applyDayNight();
                break;
            default:
                Log.e(TAG, "FOLLLOW_SYSTEM");
                break;
        }

        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
        String NightMode = preferences.getString("prefTheme", "NO");
        if (NightMode.equals("YES"))
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);
        if (NightMode.equals("NO"))
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_AUTO_BATTERY);
        else if (NightMode.equals("AUTO"))
            AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_AUTO_BATTERY);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.graphics.Paint;
import android.graphics.pdf.PdfDocument;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.Button;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import static android.Manifest.permission.READ_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;

public class MainActivity extends AppCompatActivity {

    mySQLiteDBHandler sqlLiteDBHandler;
    EditText editTextSerialNumberInsert;
    EditText editTextSerialNumberFetch;
    EditText editTextInsert;
    TextView textViewDisplay;
    Button btnInsertUpdate;

    SQLiteDatabase sqLiteDatabase;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sqlLiteDBHandler = new mySQLiteDBHandler(null,null,null,1);
        ActivityCompat.requestPermissions(this,new String[]{READ_EXTERNAL_STORAGE, WRITE_EXTERNAL_STORAGE}, PackageManager.PERMISSION_GRANTED);

        sqLiteDatabase = sqlLiteDBHandler.getWritableDatabase();

        editTextSerialNumberInsert = findViewById(R.id.editText1);
        editTextInsert = findViewById(R.id.editText2);
        editTextSerialNumberFetch = findViewById(R.id.editText3);
        textViewDisplay = findViewById(R.id.textView1);
        btnInsertUpdate = findViewById(R.id.btn_insert);
        InsertUpdateData();
    }
    
    public void InsertUpdateData() {
        btnInsertUpdate.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        boolean isUpdate = sqlLiteDBHandler.insertUpdateData(editTextSerialNumberInsert.getText().toString(),
                                editTextInsert.getText().toString());
                        if(isUpdate == true)
                            Toast.makeText(MainActivity.this,"Data Updated",Toast.LENGTH_LONG).show();
                        else
                            Toast.makeText(MainActivity.this,"Something went wrong!",Toast.LENGTH_LONG).show();
                    }
                }
        );
    }
    
    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    public void CreatePDF(View view){
        String query = "Select Text from PDFTable where SerialNumber=" + editTextSerialNumberFetch.getText().toString();
        Cursor cursor = sqLiteDatabase.rawQuery(query,null);
        try{
            cursor.moveToFirst();
            textViewDisplay.setText(cursor.getString(0));
        }
        catch (Exception e){
            e.printStackTrace();
            textViewDisplay.setText("uh-oh..");
            return;
        }

        PdfDocument pdfDocument = new PdfDocument();
        PdfDocument.PageInfo pageInfo = new PdfDocument.PageInfo.Builder(300,600,1).create();
        PdfDocument.Page page = pdfDocument.startPage(pageInfo);

        page.getCanvas().drawText(cursor.getString(0),10,25, new Paint());
        pdfDocument.finishPage(page);

        String filePath = Environment.getExternalStorageDirectory().getPath()+"/Download/"+editTextSerialNumberFetch.getText().toString()+".pdf";
        File file = new File(filePath);

        try {
            pdfDocument.writeTo(new FileOutputStream(file));
        } catch (IOException e) {
            e.printStackTrace();
        }
        pdfDocument.close();
    }
}

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import androidx.annotation.Nullable;
import static android.content.ContentValues.*;

public class mySQLiteDBHandler extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "PDFDatabase.db";
    public static final String TABLE_NAME = "PDFTable";
    public static final String COL_1 = "SerialNumber";
    public static final String COL_2 = "Text";

    public mySQLiteDBHandler(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
       super(context, name, factory, 1);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table " + TABLE_NAME +" (SERIALNUMBER TEXT,TEXT TEXT)");

    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }

    public boolean insertUpdateData(String serialnumber,String text) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COL_1,serialnumber);
        contentValues.put(COL_2,text);
        db.update(TABLE_NAME, contentValues, "SERIALNUMBER = ?", new String[] {serialnumber});
        return true;
    }
}