什么是里氏替换原则以及如何在 C# 中实现？

派生类型必须完全可替代其基类型。

定义：

我们应该能够将子类视为父类。本质上，这意味着所有派生类都应保留其父类的功能，并且不能替换父类提供的任何功能。

在 Liskov 替换之前

public class Ellipse {
public double MajorAxis { get; set; }
public double MinorAxis { get; set; }

public virtual void SetMajorAxis(double majorAxis){
this.MajorAxis = majorAxis;
}
public virtual void SetMinorAxis(double minorAxis){
this.MajorAxis = minorAxis;
}
public virtual double Area() {
return MajorAxis * MinorAxis * Math.PI;
}
}
public class Circle : Ellipse {
public override void SetMajorAxis(double majorAxis) {
base.SetMajorAxis(majorAxis);
this.MinorAxis = majorAxis; //In a cirle, each axis is identical
}
}

public class Result {
public void Method1() {
Circle circle = new Circle();
circle.SetMajorAxis(5);
circle.SetMinorAxis(4);
var area = circle.Area(); //5*4 = 20, but we expected 5*5 = 25
}
}

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利斯科夫替换后

internal class Program {
private static void Main() {
}
}
public class Ellipse {
public double MajorAxis { get; set; }
public double MinorAxis { get; set; }

public virtual void SetMajorAxis(double majorAxis) {
MajorAxis = majorAxis;
}
public virtual void SetMinorAxis(double minorAxis) {
MajorAxis = minorAxis;
}
public virtual double Area() {
return MajorAxis * MinorAxis * Math.PI;
}
}
public class Circle : Ellipse {
public override void SetMajorAxis(double majorAxis) {
base.SetMajorAxis(majorAxis);
this.MinorAxis = majorAxis; //In a cirle, each axis is identical
}
public override void SetMinorAxis(double minorAxis) {
base.SetMinorAxis(minorAxis);
this.MajorAxis = minorAxis;
}
public override double Area() {
return base.Area();
}
}

public class Circle1 {
public double Radius { get; set; }
public void SetRadius(double radius) {
this.Radius = radius;
}
public double Area() {
return this.Radius * this.Radius * Math.PI;
}
}

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