简单计算器的开发

简单计算器的开发

假设有这么一个问题：请用C++、Java、C#任意一种面向对象程序设计语言实现一个计算器控制台程序，要求输入两个数和运算符号，得到结果。你会怎么写？下面以C#为例说明。

一、看下面一个程序：

class Program

{

static void Main(string[] args)

{

Console.Write("请输入数字A：");

string A = Console.ReadLine();

Console.Write("请选择运算符号(+、-、*、/)：");

string B = Console.ReadLine();

Console.Write("请输入数字B：");

string C = Console.ReadLine();

string D = "";

if (B == "+")

D = Convert.ToString(Convert.ToDouble(A) + Convert.ToDouble(C));

if (B == "-")

D = Convert.ToString(Convert.ToDouble(A) - Convert.ToDouble(C));

if (B == "*")

D = Convert.ToString(Convert.ToDouble(A) * Convert.ToDouble(C));

if (O == "/")

D = Convert.ToString(Convert.ToDouble(A) / Convert.ToDouble(C));

Console.WriteLine("结果是：" + D);

}

}

二、代码是否规范、重构

class Program

{

static void Main(string[] args)

{

try

{

Console.Write("请输入数字A：");

string strNumberA = Console.ReadLine();

Console.Write("请选择运算符号(+、-、*、/)：");

string strOperate = Console.ReadLine();

Console.Write("请输入数字B：");

string strNumberB = Console.ReadLine();

string strResult = "";

switch (strOperate)

{

case "+":

strResult = Convert.ToString

(Convert.ToDouble(strNumberA) + Convert.ToDouble(strNumberB));

break;

case "-":

(Convert.ToDouble(strNumberA) - Convert.ToDouble(strNumberB)); break;

case "*":

strResult = Convert.ToString

(Convert.ToDouble(strNumberA) * Convert.ToDouble(strNumberB)); break;

case "/":

if (strNumberB != "0")

strResult = Convert.ToString

(Convert.ToDouble(strNumberA) / Convert.ToDouble(strNumberB));

else

strResult = "除数不能为0";

break;

}

三、复制、重用

现在要求你再写一个windows的计算器，你现在的代码能不能复用？

应该考虑：这段代码，有哪些是和控制台无关的，而只是和计算器有关的？”

四、封装

class Program

{

static void Main(string[] args)

{

try

{

Console.Write("请输入数字A：");

string strNumberA = Console.ReadLine();

Console.Write("请选择运算符号(+、-、*、/)：");

string strOperate = Console.ReadLine();

Console.Write("请输入数字B：");

string strNumberB = Console.ReadLine();

string strResult = "";

Operation.GetResult(Convert.ToDouble(strNumberA),

Convert.ToDouble(strNumberB), strOperate));

Console.WriteLine("结果是：" + strResult);

Console.ReadLine();

}

catch (Exception ex)

{

Console.WriteLine("您的输入有错：" + ex.Message);

}

}

}

public class Operation

{

public static double GetResult(double numberA, double numberB, string operate) {

double result = 0d;

switch (operate)

{

case "+":

result = numberA + numberB;

break;

case "-":

result = numberA - numberB;

break;

case "*":

result = numberA * numberB;

break;

case "/":

result = numberA / numberB;

break;

}

return result;

}

}

五、体现面向对象思想的完整程序

class Operation

{

private double _numberA = 0;

private double _numberB = 0;

///

/// 数字A

///

public double NumberA

get { return _numberA; }

set { _numberA = value; }

}

///

/// 数字B

///

public double NumberB

{

get { return _numberB; }

set { _numberB = value; }

}

///

/// 得到运算结果

///

///

public virtual double GetResult() {

double result = 0;

return result;

}

}

///

/// 加法类

///

class OperationAdd : Operation {

public override double GetResult() {

double result = 0;

result = NumberA + NumberB;

return result;

}

}

///

/// 减法类

///

class OperationSub : Operation {

public override double GetResult() {

double result = 0;

result = NumberA - NumberB;

return result;

}

}

///

/// 乘法类

///

class OperationMul : Operation

{

public override double GetResult()

{

double result = 0;

result = NumberA * NumberB;

return result;

}

}

///

/// 除法类

///

class OperationDiv : Operation

{

public override double GetResult()

{

double result = 0;

if (NumberB == 0)

throw new Exception("除数不能为0。");

result = NumberA / NumberB;

return result;

}

}

class OperationFactory

{

public static Operation createOperate(string operate) {

Operation oper = null;

switch (operate)

{

case "+":

{

oper = new OperationAdd();

break;

}

case "-":

{

oper = new OperationSub();

break;

}

case "*":

oper = new OperationMul(); break;

}

case "/":

{

oper = new OperationDiv(); break;

}

}

return oper;

}

}

依据前面内容写出JAVA计算器

由uml图可以看出Client依赖OprationFactory类，而OprationFactory类调用的是Opration接口，

当我们想给计算器增加功能时，修改客户端，增加相应的子类和在OprationFactory类的switch语句中增加相应的case语句即可，

不会影响其他的子类。

使用设计模式主要是提高代码的复用率，通过解耦合，使OprationFactory和Opration类能以后复用。

客户端界面（Java代码）

package simpleFactory.operation002;

import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.awt.event.WindowAdapter;

import java.awt.event.WindowEvent;

/**

*

* @author haiyusimon 通过继承和多态来实现各种运算的松耦合，实现通过简单工厂来产生实例

*

*/

public class Client extends Frame {

private static final long serialVersionUID = -4397773431585170565L;

TextField var_a = new TextField(10);

TextField var_b = new TextField(10);

TextField var_r = new TextField(20);

Button jia = new Button("加");

Button jian = new Button("减");

Button cheng = new Button("乘");

Button chu = new Button("除");

public static void main(String args[]) {

new Client().launchFrame("计算器");

}

/**

* @param s

*/

public void launchFrame(String s) {

setTitle(s);

setBounds(10, 10, 200, 300);

setLayout(new FlowLayout(FlowLayout.LEFT, 10, 10)); add(new Label("第一个数："));

add(var_a);

add(new Label("第二个数："));

add(var_b);

add(new Label("运算?"));

add(jia);

add(jian);

add(cheng);

add(chu);

add(new Label("结果："));

add(var_r);

pack();

setVisible(true);

addWindowListener(new WindowAdapter() {

public void windowClosing(WindowEvent e) {

System.exit(0);

}

});

jia.addActionListener(new ClientMonitor('+'));

jian.addActionListener(new ClientMonitor('-'));

cheng.addActionListener(new ClientMonitor('*'));

chu.addActionListener(new ClientMonitor('/'));

}

private class ClientMonitor implements ActionListener { char coperator = '+'; // 用来判断是哪个按钮

public ClientMonitor(char operator) {

this.coperator = operator;

}

public void actionPerformed(ActionEvent e) {

double var_aa = Double.parseDouble(var_a.getText());

double var_ab = Double.parseDouble(var_b.getText());

double r = OperationFactory.createOperation(coperator, var_aa, var_ ab);

var_r.setText("" + r);

}

}

}

工厂类：

package simpleFactory;

/**

*

* @author haiyusimon

*将由工厂类产生相应的运算类实例

*/

public class OperationFactory {

public static double createOperation(char operator,double var_aa,double var _ab) {

double r = 0.0;

Operation operation = new OprationAdd(); //使用接口，把类隐藏在接口下 switch (operator) {

case '+':

operation = new OprationAdd();

break; //最后必需有break;语句，不然将逐一运行各种情况

case '-':

operation = new OprationSub();

break;

case '*':

operation = new OprationMul();

break;

case '/':

operation = new OprationDiv();

break;

}

r = operation.getResult(var_aa, var_ab);

return r;

}

}

运算接口：

package simpleFactory;

public interface Operation {

public double getResult(double a,double b);

}

加法运算（继承运算接口）：

package simpleFactory;

public class OprationAdd implements Operation {

@Override

public double getResult(double a, double b) { return a + b;

}

}

减法运算）：

package simpleFactory;

public class OprationSub implements Operation {

@Override

public double getResult(double a, double b) { return a - b;

}

}

乘法运算（继承运算接口）：

package simpleFactory;

public class OprationMul implements Operation {

@Override

public double getResult(double a, double b) { return a * b;

}

}

除法运算：

package simpleFactory;

public class OprationDiv implements Operation {

@Override

public double getResult(double a, double b) { return a / b;

}