简单工厂模式？？

今天看了大话设计模式的简单工厂模式，不知道写的算不算，希望看到的朋友给说一下，谢谢。。。/** * @author Bo年再无木小白 * @date 2013-11-7 */import java.util.Scanner;public class Caculator {public static void main(String[] args) {Cal cal = new Cal();double num1;double num2;String mark;Scanner sc =  new Scanner(System.in);System.out.println("请输入第一个数：");num1 = sc.nextDouble();System.out.println("请输入运算符号：(+,-,*,/)");mark = sc.next();System.out.println("请输入第二个数：");num2= sc.nextInt();if(mark.equals("+")){cal.add(num1, num2);}else if(mark.equals("-")){cal.sub(num1, num2);}else if(mark.equals("*")){cal.mul(num1, num2);}else if(mark.equals("/")){cal.div(num1, num2);}else{System.out.println("您的输入有错！请检查运算符号是否书写正确！");}}}class Cal{//加法运算public  double add(double num1,double num2){double sum = 0;sum= num1+num2;System.out.println(sum);return sum;}//减法运算public  double sub(double num1,double num2){double sum = 0;sum= num1-num2;System.out.println(sum);return sum;}//乘法运算public  double mul(double num1,double num2){double sum = 0;sum= num1*num2;System.out.println(sum);return sum;}//除法运算public  double div(double num1,double num2){double sum = 0;sum= num1/num2;System.out.println(sum);return sum;}}