ASP.NET中实现封装与策略模式

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
///jisuan 的摘要说明
/// </summary>
public abstract class jisuanqi //抽象类
{
    public abstract int jisuan(int left, int right);//抽象方法
}
public class jia : jisuanqi //加法类继承抽象类
{
    public override int jisuan(int left, int right)//重写抽象方法
    {
        int jieguo = 0;
        jieguo = left + right;
        return jieguo;
    }
}
public class jian : jisuanqi
{
    public override int jisuan(int left, int right)
    {
        int jieguo = 0;
        jieguo = left - right;
        return jieguo;
    }
}
public class cheng : jisuanqi
{
    public override int jisuan(int left, int right)
    {
        int jieguo = 0;
        jieguo = left * right;
        return jieguo;
    }
}
public class chu : jisuanqi
{
    public override int jisuan(int left, int right)
    {
        int jieguo = 0;
        jieguo = left / right;
        return jieguo;
    }
}
public class Context//上下文
{
    private jisuanqi jsq = null;//基类引用对象
    public Context(jisuanqi jsp)
    {
        this.jsq = jsp;   //派生类对象jsp赋给基类对象jsq
    }
    public int jisuan(int left, int right, string fuhao)
    {
        return this.jsq.jisuan(left,right);
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void jisuan_Click(object sender, EventArgs e)
    {
        string fuhao = DropDownList1.SelectedItem.ToString();
        int left = Convert.ToInt32(TextBox1.Text);
        int right = Convert.ToInt32(TextBox2.Text);
        Context contex = null;
        if (DropDownList1.SelectedIndex == 1)
        {
            contex = new Context(new jia()); 
        }
        else if (DropDownList1.SelectedIndex == 2)
        {
            contex = new Context(new jian()); 
        }
        else if (DropDownList1.SelectedIndex == 3) 
        {
            contex = new Context(new cheng());  
        }
        else if (DropDownList1.SelectedIndex == 4) 
        {
            contex = new Context(new chu()); 
        }
        string daan = contex.jisuan(left,right,fuhao).ToString();

        string result = TextBox1.Text + DropDownList1.SelectedItem.ToString() + TextBox2.Text;
        if (TextBox3.Text == daan)     
        {
            Response.Write("回答正确!"); 
        }

        else         
        {
            Response.Write("回答错误!");
        }
    }
}