C#语言学习--基础部分(十二) －－堆，栈，装箱，拆箱，安全数据类型转换：as, is

Console Demo:

namespace BoxingDemo
{
class Circle
{
int radius;
public Circle(int radius)
{
this.radius = radius;

}
public double Area()
{
return Math.PI * radius * radius;
}
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace BoxingDemo
{
class Program
{
static void Main(string[] args)
{
Circle c = new Circle(5);
Console.WriteLine(c.Area());
int i = 10;
object o = i;//装箱
Console.WriteLine(o.ToString());
int j = (int)o; //拆箱
Console.WriteLine(j);
o = c;
if (o is int) //is 为类型判断
{
int m = (int)o;

}
else if (o is Circle)
{
Circle c2 = (Circle)o;
Console.WriteLine(c2.Area());
}
int?k = o as int?; //int? 允许int为null,默认int不能为null, as为类型转换
if (k != null)
{
Console.WriteLine(k);
}
else
{
Circle c3 = o as Circle;
if (c3 != null)
{
Console.WriteLine(c.Area());
}
}

}
}
}