android在SD卡中创建数据库

public class MyDBOpenHelper extends SQLiteOpenHelper {    PRivate Context mContext;    //db文件路径,保存在sd卡中    public static final String DB_PATH = Environment.getExternalStorageDirectory().getPath()            + File.separator + "mydata" + File.separator;    //数据库名    public static final String DB_NAME ;    //数据库版本    public static final int VERSION = 1;    static{        //判断sd卡是否正常挂载        if(! Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){            DB_NAME = "test.db";//sd卡未正常挂载,则数据库还保存在默认位置        }else{            DB_NAME = DB_PATH + "test.db";            File dbFolder = new File(DB_PATH);            // 目录不存在则自动创建目录            if (!dbFolder.exists()){                dbFolder.mkdirs();            }        }    }    public MyDBOpenHelper(Context context) {        super(context, DB_NAME, null, VERSION);//*; dbname;*;dbversion        this.mContext = context;    }    @Override    public void onCreate(SQLiteDatabase db) {        System.out.println("create");        //建表               System.out.println("create over");    }    @Override    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {        System.out.println("update");        // db.execSQL("ALTER TABLE person ADD phone VARCHAR(12) NULL");        System.out.println("update over");    }  }经过测试,当程序卸载时,数据库并不清空,重新安装程序时,onCreate()方法不执行,数据库数据依然存在.