簡單工廠模式

用一個開發計算器的例子來講解簡單工廠模式，剛開始開發這個計算器的時候程式碼是這樣的；

package out;
import java.util.Scanner;
import java.util.*;
public class SimpleFactoryPattern{

public static void main(String[]args){
        try{
            System.out.println("輸入數字A:");
            Scanner sca = new Scanner(System.in);
            Integer inA = sca.nextInt();
            String strNumberA = Integer.toString(inA);
            // System.out.println(strNumberA);
            System.out.println("輸入運算子:");
            // Scanner optscan = new Scanner(System.in);
            String optstr = sca.next();
            // Println(optstr);
            System.out.println("輸入數字B:");
            // Scanner sc
            Integer intB = sca.nextInt();
            String strNumberB = Integer.toString(intB);
            String result = "";
            Integer re = null;
            switch(optstr){
                case "+":
                re = (Integer.parseInt(strNumberA)+Integer.parseInt(strNumberB));
                result = new String(re.toString());
                System.out.println("輸出結果："+result);
                break;
                case "-":
                re = Integer.parseInt(strNumberA)-Integer.parseInt(strNumberB);
                result = new String(re.toString());
                System.out.println("輸出結果："+result);
                break;
                case "*":
                re = Integer.parseInt(strNumberA)*Integer.parseInt(strNumberB);
                result = new String(re.toString());
                System.out.println("輸出結果："+result);
                break;
                case "/":
                if(strNumberB != "0"){
                    re = Integer.parseInt(strNumberA)/Integer.parseInt(strNumberB);
                    result = new String(re.toString());
                }else{
                    result = "除數不能為0";
                }
                System.out.println("輸出結果："+result);
                break;
            }
        }catch(Exception e){
        }
}