public class Sql  extends SQLiteOpenHelper{
    //继承SQLiteOpenHelper
    //第二个参数是数据库名，第三个null，第四个是版本号
    public Sql(Context context) {
        super(context, "user", null, 1);

    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table user(id Integer primary key autoincrement,url Varchar(200),json TEXT)");
    }

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

    }
}

public class Dao {

    //

    public Dao(Context context) {
        Sql sql = new Sql(context);
        SQLiteDatabase writableDatabase = sql.getWritableDatabase();
    }



}