Android database Management---upgrade database

Package com.example.databasetest;

Import Android.content.Context;
Import Android.database.sqlite.SQLiteDatabase;
Import Android.database.sqlite.SQLiteDatabase.CursorFactory;
Import Android.database.sqlite.SQLiteOpenHelper;
Import Android.widget.Toast;

/**
* Created by Administrator on 2016/3/4.
*/
public class Databasehelper extends sqliteopenhelper{

public static final String Create_book = "CREATE table book (ID integer primary key autoincrement, author Text,price real,p Ages integer,name text) ";
public static final String create_category= "CREATE table CATEGORY (ID integer primary key autoincrement,category_name text , Category_code integer) ";
Private Context Mcontext;

Public Databasehelper (Context context, String name, Cursorfactory factory, int version) {
Super (context, name, Factory, version);
Mcontext = context;
}

@Override
public void OnCreate (Sqlitedatabase db) {
Db.execsql (Create_book);
Db.execsql (create_category);
Toast.maketext (Mcontext, "created successfully", Toast.length_short). Show ();
}

@Override
public void Onupgrade (sqlitedatabase db, int oldversion, int newversion) {
Db.execsql ("drop table if exists book");
Db.execsql ("drop table if exists Category");
OnCreate (DB);
}


}

Package com.example.datebasetest;

Import android.support.v7.app.AppCompatActivity;
Import Android.os.Bundle;
Import Android.view.View;
Import Android.widget.Button;

public class Mainactivity extends Appcompatactivity {

    Private Button btn;
    Private Databasehelper DBHelper;

    @Override
    protected void OnCreate (Bundle savedinstancestate) {
        Super.oncreate (savedinstancestate);
        Setcontentview (R.layout.activity_main);

        BTN = (Button) Findviewbyid (r.id.create_database);
        DBHelper = new Databasehelper (This, "bookstore", null,2);

        Btn.setonclicklistener (New View.onclicklistener () {
            @Override
            public void OnClick (View v) {
                Dbhelper.getwritabledatabase ();
            }
        });
    }
}

Android database Management---upgrade database