C#中的继承、重载、覆写

代码1：

using System;
using System.Text;

namespace 继承_重载_覆写
{
    class Program
    {
        static void Main(string[] args)
        {
            Person p = new Person();
            p.selfIntroduction();
            p.selfIntroduction("大家好");
            Console.WriteLine();
            Person p1 = new Person("渣渣辉","male",45);
            p1.selfIntroduction();
            p1.selfIntroduction("搭嘎好");
            Console.WriteLine();

            Student s = new Student();
            s.selfIntroduction();
            s.selfIntroduction("hello");
            Console.WriteLine();
            Student s1 = new Student("zhangsan","male",30,"123");
            s1.selfIntroduction();
            s1.selfIntroduction("hello");
            Console.WriteLine();

            Student s2 = new Student("lisi","male",30,"456");
            Person p2 = s2;//子类赋给父类（不需要强转）
            p2.selfIntroduction();//虽然是以父类的名义调用，但调的仍然是子类的方法
            p2.selfIntroduction("哈哈哈");
            Console.WriteLine();

            //Person p3 = new Person("wangwu","male",30);
            //Student s3 = (Student)p3;//父类赋给子类（需要强转），编译时没有错误，调试时报错
            //s3.selfIntroduction();
            //s3.selfIntroduction("嘿嘿嘿");
            //Console.WriteLine();

            //object obj = "chen";
            //string str = (string)obj;//父类强转子类，调试不报错
            //int n = (int)obj;//父类强转子类，调试报错，有何感想

            Person p4 = new Student("zhaoliu","male",16,"789");
            Student s4 = (Student)p4;//父类强转子类，调试不报错
            s4.selfIntroduction();
            s4.selfIntroduction("啦啦啦");
            Console.WriteLine();

            ForeignStudent fs = new ForeignStudent();
            fs.selfIntroduction();
            fs.selfIntroduction("hihihi");
            Console.WriteLine();
            ForeignStudent fs2 = new ForeignStudent("Tom","xiaoming","male",30,"911");
            fs2.selfIntroduction();
            fs2.selfIntroduction("hehehe");
            Console.WriteLine();

            StringBuilder conclusion = new StringBuilder();
            conclusion.Append("小结：\r\n");
            conclusion.Append("1.覆写不能更改方法签名\r\n");
            conclusion.Append("2.base指的是当前类的父类，不是父类的父类\r\n");
            conclusion.Append("3.父类转子类会报错，如果父类就是用子类实例化的，就不会报错\r\n");
            Console.WriteLine(conclusion.ToString());

            Console.ReadLine();
        }
    }
}

代码2：

using System;

namespace 继承_重载_覆写
{
    class Person
    {
        public string name;
        public string sex;
        public int age;

        #region 构造方法重载
        public Person()
            :this("unknownPerson","unknownPerson",-1)//这个用法仅用于构造方法，在普通方法上不能用
        {
            //Console.WriteLine("这里是默认的Person构造方法");
        }

        public Person(string name, string sex, int age)
        {
            this.name = name;
            this.sex = sex;
            this.age = age;
            //Console.WriteLine("这里是重载的Person构造方法");
        }
        #endregion

        #region 成员方法重载
        public virtual void selfIntroduction()
        {
            Console.WriteLine("Person --- 我是" + name);
        }

        public virtual string selfIntroduction(string greetings = "大家好")
        {
            Console.WriteLine("Person --- " + greetings + ",我是" + name);
            return "";
        }
        #endregion

        public void welcome()
        {
            Console.WriteLine("Person --- welcome " + name);
        }
    }
}

代码3：

using System;

namespace 继承_重载_覆写
{
    class Student : Person
    {
        public string ID;

        #region 构造方法重载
        public Student()
            : this("unknownStudent","unknownStudent",-1,"000000")
        {
            //Console.WriteLine("这里是默认的Student构造方法");
        }

        public Student(string name, string sex, int age, string ID)
            : base(name,sex,age)
        {
            this.ID = ID;
            //Console.WriteLine("这里是重载的Student构造方法");
        }
        #endregion

        public override void selfIntroduction()
        {
            base.selfIntroduction();
            Console.WriteLine("Student --- 我是" + ID);
        }
    }
}

代码4：

using System;

namespace 继承_重载_覆写
{
    class ForeignStudent : Student
    {
        public string englishName;

        public ForeignStudent()
            :this("unknwonForeignStudent", "unknwonForeignStudent", "unknwonForeignStudent",-1,"000000")
        {

        }

        public ForeignStudent(string englishName,string name,string sex,int age,string ID)
            :base(name,sex,age,ID)
        {
            this.englishName = englishName;
        }

        public override void selfIntroduction()
        {
            base.selfIntroduction();
            Console.WriteLine("ForeignStudent --- I am " + englishName);
        }
    }
}

调试结果：