里氏轉換
- 子類可以賦值給父類
- 如果父類中裝的是子類物件，那麼可以將這個父類強轉為子類物件。
1.子類可以賦值給父類
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| Student s = new Student();
Person p = s;
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所以也可以這樣寫：
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| Person p = new Student();
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例如：string.Join 也是 子類 賦值給父類的
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| string str = string.Join("|", new string[] { "1", "2", "3", "4", "5" });
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2.如果父類中裝的是子類物件，那麼可以將這個父類強轉為子類物件。
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| Person p = new Student();
Student s = (Student)p; //父類強轉為子類物件
//Teacher t = (Teacher)p; //執行會報錯，因為父類裝的是student
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is as 類型轉換
- is：表示類型轉換，轉換成功true，失敗false
- as：表示類型轉換
is 的用法
is 會用在判斷，轉換成功回傳 true, 失敗false
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| Person p = new Student(); //父類Person裝子類Student物件
//轉換失敗，因為p裝的是Student
if (p is Teacher) {
Teacher t = (Teacher)p;
t.TeacherSayHello();
} else {
Console.WriteLine("轉換失敗");
}
//轉換成功，因為p裝的是Student
if (p is Student) {
Student student = (Student)p;
student.StudentSayHello();
} else {
Console.WriteLine("轉換失敗");
}
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as 的用法
as 如果能轉換，則返回一個「對應的物件」，否則回傳null
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| Student? s = p as Student; //轉換成功，返回Student物件
s.StudentSayHello();
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| Teacher? t = p as Teacher; //null，因為p裝的是Student
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練習：創建10個物件，通過一個迴圈，去調用他們各自打招呼的方法
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| Person[] persons = new Person[10]; //宣告父類陣列
Random rnd = new Random(); //宣告產生隨機數物件
//for循環目的：通過隨機數去給每個陣列賦值(子類的物件)
for (int i = 0; i < persons.Length; i++)
{
int num = rnd.Next(1, 6); //產生隨機數1-5的數字
switch (num)//1-5
{
case 1:
persons[i] = new Student(); //子類可以賦值給父類
break;
case 2:
persons[i] = new Teacher();
break;
case 3:
persons[i] = new Men();
break;
case 4:
persons[i] = new Women();
break;
case 5:
persons[i] = new Person();
break;
}
}
//調用每個元素打招呼
for (int i = 0; i < persons.Length; i++)
{
//如果父類中裝的是子類物件，那麼可以將這個父類強轉為子類物件。
if (persons[i] is Student) //如果父類可以轉換Student成功
{
((Student)persons[i]).StudentSayHello(); //調用Student的方法
} else if (persons[i] is Teacher)
{
((Teacher)persons[i]).TeacherSayHello();
} else if (persons[i] is Men)
{
((Men)persons[i]).MenSayHello();
} else if (persons[i] is Women)
{
((Women)persons[i]).WomenSayHello();
} else
{
persons[i].SayHello(); //調用Person自己的方法
}
}
Console.ReadKey();
//父類
public class Person
{
public void SayHello()
{
Console.WriteLine("我是人類");
}
}
//子類
public class Student : Person
{
public void StudentSayHello()
{
Console.WriteLine("我是學生");
}
}
public class Teacher : Person
{
public void TeacherSayHello()
{
Console.WriteLine("我是老師");
}
}
public class Men : Person
{
public void MenSayHello()
{
Console.WriteLine("我是男人");
}
}
public class Women : Person
{
public void WomenSayHello()
{
Console.WriteLine("我是女人");
}
}
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