Connection DataBase Sqlite android

DbConnection.java

package com.cco.statrt.service;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import java.util.ArrayList;

/**
 * Created by HP on 21/06/2016.
 */
public class DbConnection extends SQLiteOpenHelper {

    public static final String DbName="student.db";
     public static final int version=1;

    //Constants for identifying table and columns
    public static final String TABLE_NOTES = "notes";
    public static final String NOTE_ID = "_id";
    public static final String NOTE_TEXT = "noteText";
    public static final String NOTE_CREATED = "noteCreated";

    SQLiteDatabase db;


    //SQL to create table
    private static final String TABLE_CREATE =
            "CREATE TABLE " + TABLE_NOTES + " (" +
                    NOTE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                    NOTE_TEXT + " TEXT, " +
                    NOTE_CREATED + " TEXT default CURRENT_TIMESTAMP" +
                    ")";

    public DbConnection(Context context) {
        super(context, DbName, null, version);
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
    sqLiteDatabase.execSQL(TABLE_CREATE);
    }

    @Override
        public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
            sqLiteDatabase.execSQL("DROP TABLE IF NOT EXISTS '"+TABLE_NOTES+"'");
        }

    public void InsertNotes(String text){
        db=getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put(NOTE_TEXT,text);
        db.insert(TABLE_NOTES,null,cv);

    }

    public void UpdateNotes(int id,String text){
        db=getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put(NOTE_TEXT,text);
        db.update(TABLE_NOTES,cv,NOTE_ID+" = ?",new String[]{Integer.toString(id)});

    }

    public void DeleteNotes(int id){
        db=getWritableDatabase();
        db.delete(TABLE_NOTES,NOTE_ID+" = ?",new String[]{Integer.toString(id)});

    }

    public ArrayList SelectNotes(){
        ArrayList array_list =new ArrayList();
        SQLiteDatabase db=this.getReadableDatabase();
        Cursor cr=db.rawQuery("select * from "+TABLE_NOTES, null);
        cr.moveToFirst();
        while(cr.isAfterLast()==false){
            array_list.add(cr.getString(cr.getColumnIndex(NOTE_ID))+":"+
                    cr.getString(cr.getColumnIndex(NOTE_TEXT)).substring(0,25)+"...");
            cr.moveToNext();
        }

        return array_list;

    }
}

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