C#面向对象编程中开闭原则的示例详解

class AreaCalculator
{
    private List<object> _shapes;

    public AreaCalculator(List<object> shapes)
    {
        _shapes = shapes;
    }

    /// <summary>
    /// 计算所有形状的面积总和
    /// </summary>
    /// <returns></returns>
    public double Sum()
    {
        List<double> areas = new List<double>();

        foreach (var item in _shapes)
        {
            if (item is Square s)
            {
                areas.Add(Math.Pow(s.SideLength, 2));
            }
            else if (item is Circle c)
            {
                areas.Add(Math.PI * Math.Pow(c.Radius, 2));
            }
        }

        return areas.Sum();
    }
}

interface IShape
{
    /// <summary>
    /// 计算面积
    /// </summary>
    /// <returns></returns>
    double CalcArea();
}

/// <summary>
/// 正方形
/// </summary>
class Square : IShape
{
    public Square(double length)
    {
        SideLength = length;
    }
    public double SideLength { get; init; }

    public double CalcArea()
    {
        return Math.Pow(SideLength, 2);
    }
}

/// <summary>
/// 圆形
/// </summary>
class Circle : IShape
{
    public Circle(double radius)
    {
        Radius = radius;
    }

    public double Radius { get; init; }

    public double CalcArea()
    {
        return Math.PI * Math.Pow(Radius, 2);
    }
}

class AreaCalculator
{
    private List<IShape> _shapes;

    public AreaCalculator(List<IShape> shapes)
    {
        _shapes = shapes;
    }

    /// <summary>
    /// 计算面积总和
    /// </summary>
    /// <returns></returns>
    public double Sum()
    {
        List<double> areas = new List<double>();

        foreach (var item in _shapes)
        {
            areas.Add(item.CalcArea());
        }

        return areas.Sum();
    }
}

/// <summary>
/// 长方形
/// </summary>
class Rectangle : IShape
{
    public Rectangle(double width, double height)
    {
        Width = width;
        Height = height;
    }

    public double Width { get; init; }
    public double Height { get; init; }

    public double CalcArea()
    {
        return Width * Height;
    }
}

class SumCalculatorOutputter
{
    protected AreaCalculator _calculator;

    public SumCalculatorOutputter(AreaCalculator calculator)
    {
        _calculator = calculator;
    }

    public string String()
    {
        return $"Sum of the areas of provided shapes: {_calculator.Sum()}";
    }

    public string JSON()
    {
        var data = new { Sum = _calculator.Sum() };
        return System.Text.json.JsonSerializer.Serialize(data);
    }
}

static void Main(string[] args)
{
    var shapes = new List<IShape> {
            new Circle(2),
            new Square(5),
            new Rectangle(2,3)
    };

    var areaCalculator = new AreaCalculator(shapes);
    var outputer = new SumCalculatorOutputter(areaCalculator);
    Console.WriteLine(outputer.JSON());
    Console.WriteLine(outputer.String());
}