C# 缺乏多重继承是如何导致需要接口的

C# 缺乏多重继承是如何导致需要接口的？

csharp
// 定义一个接口
public interface IShape
{
    double GetArea();
    double GetPerimeter();
}
// 实现接口的类
public class Rectangle : IShape
{
    private double length;
    private double width;
    public Rectangle(double length, double width)
    {
        this.length = length;
        this.width = width;
    }
    public double GetArea()
    {
        return length * width;
    }
    public double GetPerimeter()
    {
        return 2 * (length + width);
    }
}
// 实现接口的类
public class Circle : IShape
{
    private double radius;
    public Circle(double radius)
    {
        this.radius = radius;
    }
    public double GetArea()
    {
        return Math.PI * radius * radius;
    }
    public double GetPerimeter()
    {
        return 2 * Math.PI * radius;
    }
}
// 使用接口实现多重继承的效果
public class Square : IShape
{
    private double side;
    public Square(double side)
    {
        this.side = side;
    }
    public double GetArea()
    {
        return side * side;
    }
    public double GetPerimeter()
    {
        return 4 * side;
    }
}
// 测试代码
class Program
{
    static void Main(string[] args)
    {
        Rectangle rectangle = new Rectangle(5, 3);
        Console.WriteLine("Rectangle area: " + rectangle.GetArea());
        Console.WriteLine("Rectangle perimeter: " + rectangle.GetPerimeter());
        Circle circle = new Circle(2);
        Console.WriteLine("Circle area: " + circle.GetArea());
        Console.WriteLine("Circle perimeter: " + circle.GetPerimeter());
        Square square = new Square(4);
        Console.WriteLine("Square area: " + square.GetArea());
        Console.WriteLine("Square perimeter: " + square.GetPerimeter());
    }
}