解释下C#中的语句，有追加分

public static void main()
{
colleague colleague1=new colleague();//实例化一个colleague对象
colleague1.m_name="yang"; //colleague的name属性赋值
colleague1.m_telephone="111111";//colleague的telephone属性赋值
if(colleague1 is contact) //colleague1 是否为contact类型
{
contact contact1=(contact) colleague1;//如果是强制转换为contact类型
contact1.dialnumber(); //调用contact1的dialnumber方法
}
else
console.writeline("fail;",colleague1.m_name //出处转化失败
);
contact contact2 =new contact(); //类似上面colleague的实例
if (contact2 is colleague)
{
colleague colleague2=(colleague) contact2;
colleague2.sendfax("Hello");
}
else
console.writeline("lsdfjlsdfjsdflkj",contact2.m_name);
}

}

这样解释应该清楚了吧

colleague是用户自己定义的一个类
colleague1.m_name和colleague1.m_telephone是这个类的属性
colleague2.sendfax是这个类的方法
contact contact1=(contact) colleague1