實現一個計算器：要求輸入2個數，和運算符，得到結果

package com.pb.demo1;public class Operation {    PRivate double num1;    private double num2;        public double getResult(double num1,double num2){        double result=0;        return result;    }    public double getNum1() {        return num1;    }    public void setNum1(double num1) {        this.num1 = num1;    }    public double getNum2() {        return num2;    }    public void setNum2(double num2) {        this.num2 = num2;    }    }

package com.pb.demo1;/* * 加法 */public class AddOperation extends Operation {    @Override    public double getResult(double num1, double num2) {                return (num1+num2);    }}

package com.pb.demo1;/* * 減法 */public class Substruction extends Operation {    @Override    public double getResult(double num1, double num2) {            return (num1-num2);    }    }

package com.pb.demo1;/* * 乖法 */public class Multiplication extends Operation {    @Override    public double getResult(double num1, double num2) {                return (num1*num2);    }    }

package com.pb.demo1;/* * 除法 */public class Division extends Operation {    @Override    public double getResult(double num1, double num2) {                return (num1/num2);    }    }

package com.pb.demo1;/* * 取余 */public class ModeOperation extends Operation {    @Override    public double getResult(double num1, double num2) {                return (num1%num2);    }    }

package com.pb.demo1;/* * 簡單工廠類 */public class Factory {   //返回類型 為類對象    public Operation getResult(String op){        Operation operation=null;        //根據操作符來聲明對象并返回        switch (op){        case "+":            operation=new AddOperation();            break;        case "-":            operation=new Substruction();            break;        case "*":            operation=new Multiplication();            break;        case "/":            operation=new Division();;            break;        case "%":            operation=new ModeOperation();            break;            default:                System.err.println("輸入運算符不正確!");                break;        }        //返回生成的對象        return operation;    }}

package com.pb.demo1;import java.util.InputMismatchException;import java.util.Scanner;/* * 計算器 */public class Demo1 {    public static void main(String[] args) {        //聲明掃描器類型變量        Scanner  input =new Scanner(System.in);        //聲明工廠對象        Factory fac=new Factory();    try{        System.out.println("請輸入第一個整數:");        double num1=input.nextDouble();        System.out.println("請輸入第二個整數:");        double num2=input.nextDouble();        System.out.println("請輸運算符:+、-、*、/、%");        String op=input.next();        //接收工廠的返回對象 工廠根據操作符生成的對象        Operation operation=fac.getResult(op);        //接收計算結果            double result=operation.getResult(num1, num2);            //顯示計算結果            System.out.println(num1+"與"+num2+"的運行結果:"+result);    }catch(InputMismatchException e){        System.err.println("輸入類型不正確!");        }catch(Exception e){        e.printStackTrace();    }    }}