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public virtual double Area()
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{
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return x * y;
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}
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调用虚方法时,将为重写成员检查该对象的运行时类型。将调用大部分派生类中的该重写成员,如果没有派生类重写该成员,则它可能是原始成员。
默认情况下,方法是非虚拟的。不能重写非虚方法。
virtual 修饰符不能与 static、abstract 和 override 修饰符一起使用。
除了声明和调用语法不同外,虚拟属性的行为与抽象方法一样。
-
在静态属性上使用 virtual 修饰符是错误的。
-
通过包括使用 override 修饰符的属性声明,可在派生类中重写虚拟继承属性。
在该示例中,Dimensions
类包含 x
和 y
两个坐标和 Area()
虚方法。不同的形状类,如 Circle
、Cylinder
和 Sphere
继承 Dimensions
类,并为每个图形计算表面积。每个派生类都有各自的 Area()
重写实现。根据与此方法关联的对象,通过调用正确的 Area()
实现,该程序为每个图形计算并显示正确的面积。
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// cs_virtual_keyword.cs
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using System;
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class TestClass
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{
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public class Dimensions
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{
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public const double PI = Math.PI;
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protected double x, y;
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public Dimensions()
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{
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}
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public Dimensions(double x, double y)
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{
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this.x = x;
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this.y = y;
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}
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public virtual double Area()
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{
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return x * y;
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}
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}
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public class Circle : Dimensions
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{
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public Circle(double r) : base(r, 0)
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{
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}
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public override double Area()
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{
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return PI * x * x;
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}
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}
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class Sphere : Dimensions
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{
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public Sphere(double r) : base(r, 0)
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{
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}
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public override double Area()
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{
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return 4 * PI * x * x;
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}
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}
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class Cylinder : Dimensions
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{
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public Cylinder(double r, double h) : base(r, h)
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{
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}
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public override double Area()
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{
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return 2 * PI * x * x + 2 * PI * x * y;
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}
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}
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static void Main()
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{
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double r = 3.0, h = 5.0;
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Dimensions c = new Circle(r);
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Dimensions s = new Sphere(r);
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Dimensions l = new Cylinder(r, h);
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// Display results:
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Console.WriteLine("Area of Circle = {0:F2}", c.Area());
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Console.WriteLine("Area of Sphere = {0:F2}", s.Area());
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Console.WriteLine("Area of Cylinder = {0:F2}", l.Area());
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}
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}
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