Ben Huang's Blog

subtypes(衍生型別): 類別

base Types(基底型別): 介面、抽象類別、基底類別

LSP的精神:

• 每個衍生類別轉型時都能正確轉為基底類別
• 必須正確實作繼承與多型

第一版：沒有繼承，單純計算矩形面積

using System;

public class Program
{
	public static void Main()
	{
		Rectangle o = new Rectangle();
		o.Width = 40;
		o.Height = 50;
		LSPBehavior.GetArea(o).Dump();
	}
}

public class Rectangle
{
	public int Height
	{
		get;
		set;
	}

	public int Width
	{
		get;
		set;
	}
}

public class LSPBehavior
{
	public static int GetArea(Rectangle s)
	{
		if (s.Width > 20)
		{
			s.Width = 20;
		}

		return s.Width * s.Height;
	}
}

 新增需求，增加 Square 類別 (套用 OCP 原則) 

using System;

public class Program
{
	public static void Main()
	{
		Square o = new Square();
		o.Width = 40;
		// o.Height = 50;
		LSPBehavior.GetArea(o).Dump();

	}
}

public class Rectangle
{
	public virtual int Height
	{
		get;
		set;
	}

	public virtual int Width
	{
		get;
		set;
	}
}

public class LSPBehavior
{
	public static int GetArea(Rectangle s)
	{
		if (s.Width > 20)
		{
			s.Width = 20;
		}

		return s.Width * s.Height;
	}
}

public class Square : Rectangle
{
	private int _height;
	private int _width;
	public override int Height
	{
		get
		{
			return _height;
		}

		set
		{
			_height = _width = value;
		}
	}

	public override int Width
	{
		get
		{
			return _width;
		}

		set
		{
			_width = value;
			_height = value;
		}
	}
}