GOF之构建器模式

动机(Motivation)

在软件系统中，有时候面临着“一个复杂对象”的创建工作，其通常由各个部分的子对象用一定的算法构成;由于需求的变化，这个复杂对象的各个部分经常面临着剧烈的变化，但是将他们组合在一起的算法却相对稳定。

如何应对这种变化》如何提供一种“封装机制”来隔离出“复杂对象的各个部分”的变化，从而保持系统中的“稳定构建算法”不随着需求改变而改变？

意图(Intent)

将一个复杂复杂对象的构建与其表示相分离，使得同样的构建过程可以创建不同的表示。

结构(Structure)

代码实现

对应Builder部分 
public abstract class Builder
    {
        public abstract Door BuildeDoor();
        public abstract Window BuildeWindow();
        public abstract Floor BuildeFloor();

        public abstract House GetHouse();
    }
    public abstract class House
    {
        private Door door;

        public Door Door
        {
            get { return door; }
            set { door = value; }
        }
        private Window window;

        public Window Window
        {
            get { return window; }
            set { window = value; }
        }
        private Floor floor;

        public Floor Floor
        {
            get { return floor; }
            set { floor = value; }
        }
        public abstract void SayHello();
    }
    public abstract class Door
    {
        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }
    public abstract class Window
    {
        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }
    public abstract class Floor
    {
        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
    }

对应ConcreteBuilder部分
public class ModenBuilder : Builder
    {
        private Door door;
        private Window window;
        private Floor floor;
        public override Door BuildeDoor()
        {
            door = new ClassicDoor("古典的门");
            return door;
        }

        public override Window BuildeWindow()
        {
            window = new ModenWindow("摩登的窗");
            return window;
        }

        public override Floor BuildeFloor()
        {
            floor = new ModenFloor("摩登的楼");
            return floor;
        }

        public override House GetHouse()
        {
            return new ModenHouse(door,window,floor);
        }
    }
    public class ClassicDoor : Door
    {
        public ClassicDoor(string name)
        {
            this.Name = name;
        }
    }
    public class ModenWindow : Window
    {
        public ModenWindow(string name)
        {
            this.Name = name;
        }
    }
    public class ModenFloor : Floor
    {
        public ModenFloor(string name)
        {
            this.Name = name;
        }
    }
    public class ModenHouse:House
    {
        public ModenHouse(Door door, Window window, Floor floor)
        {
            this.Door = door;
            this.Window = window;
            this.Floor = floor;
        }
        public override void SayHello()
        {
            Console.WriteLine("{0}-----{1}---------{2}",this.Door.Name,this.Window.Name,this.Floor.Name);
        }
    }

对应Director部分
 public class Manager
    {
        public static House GetHouse(Builder builder)
        {
            builder.BuildeDoor();
            builder.BuildeWindow();
            builder.BuildeFloor();

            return builder.GetHouse();
        }
    }

主函数的调用
 static void Main(string[] args)
        {
            House house = Manager.GetHouse(new ModenBuilder());
            house.SayHello();
            Console.ReadKey();

        }

Builder模式的几个要点

Builder模式主要用于“分步骤构建一个复杂的对象”。在其中“分步骤”是一个稳定的算法，而复杂对象的各个部分则经常变化。

变化点在哪里，封装哪里---Builder模式主要在于应对“复杂对象各个部分”的频繁需求变动。其缺点在于难以应对“分步骤构建算法”的需求变动。

Abstract Factory模式解决“系列对象”的需求变化，Builder模式解决“对象部分”的需求变化。Builder模式通常个Composite模式组合使用。