动机:
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了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,但是将它们组合在一起的算法却欲相对稳定。
如何应对这种变化?如何提供一种“封闭机制”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:
将一个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。
出自:《设计模式》GoF
Builder模式的几个要点:
1、Builder模式主要用于“分步骤构建一个复杂的对象”。在这其中“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。
2、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。
3、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模式通常和Composite模式组合使用。
稳定部分:
public abstract class Builder
{
public abstract void BuildDoor();
public abstract void BuildWall();
public abstract void BuildFloor();
public abstract void BuildWindows();
public abstract void BuildHouseCeiling();
public abstract House GetHouse();
}
public abstract class Door
{
}
public abstract class Wall
{
}
public abstract class Windows
{
}
public abstract class Floor
{
}
public abstract class HouseCeiling
{
}
public class GameManager
{
Builder builder;
public GameManager(Builder builder)
{
this.builder = builder;
}
public static House CreateHouse()
{
builder.BuildDoor();
builder.BuildDoor();
builder.BuildWall();
builder.BuildWall();
builder.BuildWindows();
builder.BuildWindows();
builder.BuildFloor();
builder.BuildHouseCeiling();
return builder.GetHouse();
}
}
{
public abstract void BuildDoor();
public abstract void BuildWall();
public abstract void BuildFloor();
public abstract void BuildWindows();
public abstract void BuildHouseCeiling();
public abstract House GetHouse();
}
public abstract class Door
{
}
public abstract class Wall
{
}
public abstract class Windows
{
}
public abstract class Floor
{
}
public abstract class HouseCeiling
{
}
public class GameManager
{
Builder builder;
public GameManager(Builder builder)
{
this.builder = builder;
}
public static House CreateHouse()
{
builder.BuildDoor();
builder.BuildDoor();
builder.BuildWall();
builder.BuildWall();
builder.BuildWindows();
builder.BuildWindows();
builder.BuildFloor();
builder.BuildHouseCeiling();
return builder.GetHouse();
}
}
变化部分:
public class DoorA : Door
{
}
public class WallA : Wall
{
}
public class WindowsA : Windows
{
}
public class FloorA : Floor
{
}
public class HouseCeilingA : HouseCeiling
{
}
public class HouseBuilderA : Builder
{
public override void BuildDoor()
{
}
public override void BuildWallr()
{
}
public override void BuildWindows()
{
}
public override void BuildFloor()
{
}
public override void BuildHouseCeiling()
{
}
public override House GetHouse()
{
}
}
{
}
public class WallA : Wall
{
}
public class WindowsA : Windows
{
}
public class FloorA : Floor
{
}
public class HouseCeilingA : HouseCeiling
{
}
public class HouseBuilderA : Builder
{
public override void BuildDoor()
{
}
public override void BuildWallr()
{
}
public override void BuildWindows()
{
}
public override void BuildFloor()
{
}
public override void BuildHouseCeiling()
{
}
public override House GetHouse()
{
}
}
主程序:
//应用于构建一个对象过程是稳定的
public static void Main()
{
//变化点
GameManager g = new GameManager(new HouseBuilderA());
//GameManager g = new GameManager(new HouseBuilderB());
House h = GameManager.CreateHouse();
}
public static void Main()
{
//变化点
GameManager g = new GameManager(new HouseBuilderA());
//GameManager g = new GameManager(new HouseBuilderB());
House h = GameManager.CreateHouse();
}