繼承中的構(gòu)造方法：
1、創(chuàng)建子類對象時，一定會先創(chuàng)建父類對象
2、如果調(diào)用的子類構(gòu)造方法沒有使用base，就會自動調(diào)用父類無參的構(gòu)造方法，
?? 如果父類沒有無參的構(gòu)造方法就會報錯
3、如果調(diào)用的子類構(gòu)造方法使用了base，就會根據(jù)base后面的參數(shù)調(diào)用父類對應(yīng)的構(gòu)造方法

注意：如果類中有定義有參的構(gòu)造方法，建議把無參的構(gòu)造方法也寫出來

里氏替換原理：子類對象能替換父類對象，父類對象不能替換子類對象

is:判斷類型是否匹配、兼容
as:對引用類型進行類型轉(zhuǎn)換（特點：轉(zhuǎn)換失敗不會報異常，而是返回一個null）
強制轉(zhuǎn)換：轉(zhuǎn)換失敗會拋出異常

?

　　/// <summary>
??? /// 父類
??? /// </summary>
??? class Person
??? {
??????? //姓名
??????? public string Name { get; set; }
??????? //年齡
??????? public int Age { get; set; }
??????? //職業(yè)
??????? public string Job { get; set; }

??????? //注意：如果類中有定義有參的構(gòu)造方法，建議把無參的方法也寫出來
??????? public Person() { Console.WriteLine("Person的無參構(gòu)造方法被調(diào)用了！"); }

??????? public Person(string name, int age,string job)
??????? {
??????????? this.Name = name;
??????????? this.Age = age;
??????????? this.Job = job;
??????????? Console.WriteLine("Person帶3個參數(shù)的構(gòu)造方法被調(diào)用！");
??????? }

??????? public void Eat()
??????? {
??????????? Console.WriteLine("吃飯");
??????? }

??????? public void Sleep()
??????? {
??????????? Console.WriteLine("睡覺");
??????? }
??? }

?

//子類

class Student:Person
??? {
??????? //特長
??????? public string Special { get; set; }
??????? //學習
??????? public void Study()
??????? {
??????????? Console.WriteLine("學習");
??????? }
??? }

class Teacher:Person
??? {
??????? //教齡
??????? public int TeachYear { get; set; }

??????? public Teacher()
??????? {
??????????? Console.WriteLine("Teacher無參構(gòu)造方法被調(diào)用！");
??????? }

??????? public Teacher(string name,int age,string job,int teachYear):base(name,age,job)
??????? {
??????????? this.TeachYear = teachYear;
??????????? Console.WriteLine("Teacher帶四個參數(shù)的構(gòu)造方法被調(diào)用！");
??????? }

??????? public new void Eat()
??????? {
??????????? Console.WriteLine("老師吃飯");
??????? }

??????? public void Teach()
??????? {
??????????? Console.WriteLine("教書");
??????? }
??? }

//使用

?class Program
??? {
??????? //繼承中的構(gòu)造方法
??????? //static void Main(string[] args)
??????? //{
??????? //??? //Teacher teacher = new Teacher();
??????? //??? Teacher teacher = new Teacher("張三",23,"程序員",2);
??????? //??? teacher.Eat();
??????? //}

??????? //is:判斷類型是否匹配、兼容
??????? //static void Main(string[] args)
??????? //{
??????? //??? Student stu = new Student();
??????? //??? Console.WriteLine(stu is Student);//true
??????? //??? Console.WriteLine(stu is Teacher);//false
??????? //??? Console.WriteLine(stu is Person);//true
??????? //}

??????? //里氏替換原理
??????? //static void Main(string[] args)
??????? //{
??????? //??? Person p1 = new Person();
??????? //??? Person p2 = new Teacher();//正確，子類對象替換父類對象
??????? //??? Teacher t = new Teacher();
??????? //??? Teacher t2 = new Person();//錯誤，父類對象不能替換子類對象
??????? //}

??????? //as：對引用類型進行類型轉(zhuǎn)換（特點：轉(zhuǎn)換失敗不會報異常，而是返回一個null）
??????? static void Main(string[] args)
??????? {
??????????? Person p = new Teacher();
??????????? //Console.WriteLine(p.TeachYear);//出錯，因為p無法訪問TeachYear(因為編譯器認為p為Person類型)
??????????? Console.WriteLine((p as Teacher).TeachYear);//正確，因為p已經(jīng)轉(zhuǎn)換為了Teacher

??????????? Console.WriteLine(p as Student);//轉(zhuǎn)換失敗，結(jié)果為null
??????????? Console.WriteLine((Student)p);//轉(zhuǎn)換失敗，出現(xiàn)異常
??????? }
??? }

?

轉(zhuǎn)載于:https://www.cnblogs.com/danmao/p/3871787.html

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