c#語言-------------型別轉換2（裡式轉換）
阿新 • • 發佈：2019-01-25
一、裡式轉換（在C#中一切類都直接或間接繼承與Object類）
1、子類可以賦值給父類:實質如果一個地方需要一個父類做為引數，我們可以給一個子類代替（一個方法中需要傳進一個子類的物件，子類做實參，我們可以讓父類作為形參接收子類的物件）
2、如果父類中裝的是子類的物件，那麼可以將這個父類轉換為子類物件
**子類物件可以呼叫父類中的成員，但是父類物件只能呼叫自己的成員
3、
is：表示型別轉換，如果轉換成功，則返回一個true，否則返回一個false
as：表示型別轉換，如果能轉換則返回對應的物件，否則返回一個null
裡式轉換法（子類可以賦值給父類）
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace 里氏轉換法1 { class Program { static void Main(string[] args) { //子類可以賦值給父類：實質如果一個地方需要一個父類做為引數，我們可以給一個子類代替（一個方法中需要傳進一個子類的物件，子類做實參，我們可以讓父類作為形參接收子類的物件） Student stu1 = new Student(); Person per1 = stu1;// Person per2 = new Student(); Person per3 = new Teacher(); string str = string.Join("|", new string[] { "1", "2", "3", "4" });//這裡也用到里氏轉換法 Console.WriteLine(str); //如果父類中裝的是子類的物件，那麼可以將這個父類的物件強轉為子類物件 Student st1 = (Student)per1; st1.StudentSayHello(); Student st2 = (Student)per2; st2.StudentSayHello(); Teacher tc3 = (Teacher)per3; tc3.TeacherSayHello(); //Teacher tc4 = (Teacher)per1;//會丟擲異常因為per1中裝的是Student類的物件 Console.ReadKey(); } } public class Person { public void PersonSayHello() { Console.WriteLine("我是父類"); } } public class Student:Person { public void StudentSayHello() { Console.WriteLine("我是學生類"); } } public class Teacher : Person { public void TeacherSayHello() { Console.WriteLine("我是老師類"); } } }
執行結果：
裡式轉換法is的用法
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace 里氏轉換法2之is { class Program { static void Main(string[] args) { //子類可以賦值給父類：實質如果一個地方需要一個父類做為引數，我們可以給一個子類代替（一個方法中需要傳進一個子類的物件，子類做實參，我們可以讓父類作為形參接收子類的物件） Student stu1 = new Student(); Person per1 = stu1;// Person per2 = new Student(); Person per3 = new Teacher(); //如果父類中裝的是子類的物件，那麼可以將這個父類的物件強轉為子類物件 //is的用法 //Student st1 = (Student)per1; //st1.StudentSayHello(); if (per1 is Student) { Student st1 = (Student)per1; st1.StudentSayHello(); } else { Console.WriteLine("轉換失敗"); } //Student st2 = (Student)per2; //st2.StudentSayHello(); if (per2 is Student) { Student st2 = (Student)per2; st2.StudentSayHello(); } else { Console.WriteLine("轉換失敗"); } //Teacher tc3 = (Teacher)per3; //tc3.TeacherSayHello(); if (per3 is Teacher) { Teacher tc3 = (Teacher)per3; tc3.TeacherSayHello(); } else { Console.WriteLine("轉換失敗"); } //Teacher tc4 = (Teacher)per1;//會丟擲異常因為per1中裝的是Student類的物件 if (per1 is Teacher) { Teacher tc4 = (Teacher)per1; tc4.TeacherSayHello(); } else { Console.WriteLine("轉換失敗"); } Console.ReadKey(); } } public class Person { public void PersonSayHello() { Console.WriteLine("我是父類"); } } public class Student : Person { public void StudentSayHello() { Console.WriteLine("我是學生類"); } } public class Teacher : Person { public void TeacherSayHello() { Console.WriteLine("我是老師類"); } } }
執行結果：
裡式轉換法as的使用：
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace 里氏轉換法3之as { class Program { static void Main(string[] args) { //子類可以賦值給父類：實質如果一個地方需要一個父類做為引數，我們可以給一個子類代替（一個方法中需要傳進一個子類的物件，子類做實參，我們可以讓父類作為形參接收子類的物件） Student stu1 = new Student(); Person per1 = stu1;// Person per2 = new Student(); Person per3 = new Teacher(); //如果父類中裝的是子類的物件，那麼可以將這個父類的物件強轉為子類物件 //as的用法 Student st1 = per1 as Student; st1.StudentSayHello(); Student st2 = per2 as Student; st2.StudentSayHello(); Teacher tc1 = per3 as Teacher; tc1.TeacherSayHello(); Teacher tc2 = per1 as Teacher;//tc2中是null Console.WriteLine("======分割線======"); Console.WriteLine(st1); Console.WriteLine(st2); Console.WriteLine(tc1); Console.WriteLine(tc2); Console.WriteLine("上面的tc2裡面是空即什麼也打印不出來"); Console.WriteLine("下面的t也為空即在下面的兩個分割線內什麼也打印不出來"); Console.WriteLine("======分割線======"); Teacher t = null; Console.WriteLine(t); Console.WriteLine("======分割線======"); Console.WriteLine("結束"); Console.ReadKey(); } } public class Person { public void PersonSayHello() { Console.WriteLine("我是父類"); } } public class Student : Person { public void StudentSayHello() { Console.WriteLine("我是學生類"); } } public class Teacher : Person { public void TeacherSayHello() { Console.WriteLine("我是老師類"); } } }
執行結果：
里氏轉換法的練習：每次顯示的結果都是隨機的
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace 里氏轉換法4之練習
{
class Program
{
static void Main(string[] args)
{
Person[] pers = new Person[10];//宣告一個Person型別的陣列來存Person類的物件（里氏轉換法可知也可存Person的子類）
Random r = new Random();
for (int i = 0; i < pers.Length; i++)//作用：通過隨機數給給我們的陣列賦值
{
int rNum = r.Next(1, 8);
switch (rNum)
{
case 1:pers[i] = new Chinese();
break;
case 2: pers[i] = new Person();
break;
case 3: pers[i] = new English();
break;
case 4: pers[i] = new American();
break;
case 5: pers[i] = new Russian();
break;
case 6: pers[i] = new French();
break;
case 7: pers[i] = new German();
break;
}
}
for (int i = 0; i < pers.Length; i++)
{
if (pers[i] is Chinese)
{
((Chinese)pers[i]).ChineseSay();
}
else if (pers[i] is English)
{
((English)pers[i]).EnglishSay();
}
else if (pers[i] is American)
{
((American)pers[i]).AmericanSay();
}
else if (pers[i] is French)
{
((French)pers[i]).FrenchSay();
}
else if (pers[i] is Russian)
{
((Russian)pers[i]).RussianSay();
}
else if (pers[i] is German)
{
((German)pers[i]).GermanSay();
}
else
{
pers[i].PersonSay();
}
}
Console.ReadKey();
}
}
public class Person
{
public void PersonSay()
{
Console.WriteLine("我是人類");
}
}
public class Chinese : Person
{
public void ChineseSay()
{
Console.WriteLine("我是中國人");
}
}
public class English : Person
{
public void EnglishSay()
{
Console.WriteLine("我是英國人");
}
}
public class American : Person
{
public void AmericanSay()
{
Console.WriteLine("我是美國人");
}
}
public class Russian : Person
{
public void RussianSay()
{
Console.WriteLine("我是俄羅斯人");
}
}
public class German : Person
{
public void GermanSay()
{
Console.WriteLine("我是德國人");
}
}
public class French : Person
{
public void FrenchSay()
{
Console.WriteLine("我是法國人");
}
}
}執行結果：
