C# Keyword(base,protected, override,....)
(1)protected
The protected keyword is a member access modifier. A protected member is accessible from within the class in which it is declared, and from within any class derived from the class that declared this member.
//proteted修饰的方法 (本类 和 派生类 内部可访问)
class A { protected int x = 123; } class B : A { void F() { A a = new A(); B b = new B(); a.x = 10; // Error b.x = 10; // OK } }
(2)base
The base keyword is used to access members of the base class from within a derived class:
- Call a method on the base class that has been overridden by another method.
- Specify which base-class constructor should be called when creating instances of the derived class.
(用于访问基类的成员,仅限于在派生类内部. base.方法名())
A base class access is permitted only in a constructor, an instance method, or an instance property accessor.
(只可在派生类(derived class)的 构造函数,实例方法,实例属性 中用base访问基类)
// keywords_base.cs // Accessing base class members using System; public class Person { protected string ssn = "444-55-6666"; protected string name = "John L. Malgraine"; public virtual void GetInfo() { Console.WriteLine("Name: {0}", name); Console.WriteLine("SSN: {0}", ssn); } } class Employee: Person { public string id = "ABC567EFG"; public override void GetInfo() { // Calling the base class GetInfo method: base.GetInfo(); Console.WriteLine("Employee ID: {0}", id); } } class TestClass { public static void Main() { Employee E = new Employee(); E.GetInfo(); } }
结果:
Name:John L. Malgraine
SSN:444-55-6666
Employee ID:ABC567EFG
(3) virtual -overrid (必配套使用)
基类中用virtual修饰的方法,在派生类中可用override重写
class TestClass { public class Shape { public const double PI = Math.PI; protected double x, y; public Shape() { } public Shape(double x, double y) { this.x = x; this.y = y; } public virtual double Area() { return x * y; } } public class Circle : Shape { public Circle(double r) : base(r, 0) { } public override double Area() { return PI * x * x; } } class Sphere : Shape { public Sphere(double r) : base(r, 0) { } public override double Area() { return 4 * PI * x * x; } } class Cylinder : Shape { public Cylinder(double r, double h) : base(r, h) { } public override double Area() { return 2 * PI * x * x + 2 * PI * x * y; } } static void Main() { double r = 3.0, h = 5.0; Shape c = new Circle(r); Shape s = new Sphere(r); Shape l = new Cylinder(r, h); // Display results: Console.WriteLine("Area of Circle = {0:F2}", c.Area()); Console.WriteLine("Area of Sphere = {0:F2}", s.Area()); Console.WriteLine("Area of Cylinder = {0:F2}", l.Area()); } } /* Output: Area of Circle = 28.27 Area of Sphere = 113.10 Area of Cylinder = 150.80 */