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Patterns In Java

TiGERTiAN — Thu, 11 Oct 2007 04:40:00 GMT

http://www.jdon.com/designpatterns/

TiGERTiAN 2007-10-11 12:40 发表评论

Abstract Factory Pattern

TiGERTiAN — Thu, 26 Apr 2007 13:11:00 GMT

provide an interface for creating families of related or dependent objects without specifying their concrete classes
--Gamma, E., Helm, R., Johnson, R., Vlissides, J. Design Patterns: Elements of Reusable Object-Oriented Software, Boston: Addison-Wesley, 1995, p.87

讲白�?ji��n)，��是面向抽象接口�~�程�Q�每一�l�对象都实现同一个接�?nbsp;

abstract class ResFactory {
   abstract public DisplayDriver getDispDrvr();
   abstract public PrintDriver getPrtDrvr();
}

class LowResFact extends ResFactory {
   public DisplayDriver getDispDrvr() {
      return new LRDD();
   }
   public PrintDriver getPrtDrvr() {
      return new LRPD();
   }
}

class HighResFact extends ResFactory {
   public DisplayDriver getDispDrvr() {
      return new HRDD();
   }
   public PrintDriver getPrtDrvr() {
      return new HRPD();
  }
}

比如说我需要一个显卡驱动和打印机驱动，高档机和低档机驱动都不一��P��但我不想用很多switch来选择�Q�这样很�ȝ��(ch��)�Q�而且扩展更麻�?ch��)。那我就定义一个抽象类�Q�将我需要调用的资源全部攑֜�里面�Q�初始化�cȝ��时候我们可以先声明一�?br>ResFactory factory;
当我们需要��用高档机的时候就
factory=new HighResFact();
使用低档机的时候就
factory=new LowResFact();

�q�样�Q�就可以很方便的调用自己惌��用的对象�Q�而且不用考虑有没有提供相应方法，在扩展和修改的时候更加方便，因�ؓ(f��)抽象和实现全部分开�?ji��n)，�q�也是我们在�q�_��~�程当中需要注意的�?br>

TiGERTiAN 2007-04-26 21:11 发表评论

Bridge Pattern

TiGERTiAN — Sun, 08 Apr 2007 06:27:00 GMT

桥接模式�Q�引�?#8220;四�h帮的�?#8221;��是 “decouple an abstraction from its implementation so that the two can vary independently”�Q�抽象与行�ؓ(f��)分离�?br>
说个例子

客户想画图，��M��U�圆和矩形，每种矩�Ş都要调用特别的划�U�（draw_a_line()�Q�方法，每一�U�圆也是。如果像上面那样�Q�是不是感觉混�ؕ�?ji��n)点�Q�看看下面的呢�?br>
�q�个是不是舒服点�Q�的��，囑�Ş和画法都存在一一对应的关�p�，我们完全可以把图形这个抽象和��L��q�个行�ؓ(f��)分离�Q�而不需要一个画法对应多个抽象，如上面那个�?br>

public abstract class Shape
{
    public abstract void draw();
}

//�ȝ��和圆的方�?/span>
public abstract class ShapeDrawing
{
    public abstract void draw_a_line();
    public abstract void draw_a_circle();
}

public class ShapeDrawingSingleton
{
    private static ShapeDrawing shapedrawingSingleton;

    public ShapeDrawingSingleton(ShapeDrawing shapedrawing)
    {
        shapedrawingSingleton=shapedrawing;
    }

    public static ShapeDrawing getShapeDrawing()
    {
        return shapedrawingSingleton;
    }
}

//��d��Ҏ(gu��)��基类
public class VShape extends Shape
{
    public ShapeDrawing shapedrawing;

    public void setShapeDrawing()
    {
        this.shapedrawing=ShapeDrawingSingleton.getShapeDrawing();
    }

    public ShapeDrawing getShapeDrawing()
    {
        return this.shapedrawing;
    }
}

public class V1Circle extends VShape
{
    public Circle(){setShapeDrawing();}

    public void draw()
    {
        //用shapedrawing��d��
        //shapedrawing.draw_a_circle()
    }
}

//
//V1Rectangle和V2�p�d��参照上面�?br>//

public class DP1ShapeDrawing extends ShapeDrawing
{
    public void draw_a_line(){};
    public void draw_a_circle(){};
}

public class DP2ShapeDrawing extends ShapeDrawing
{
    public void draw_a_line(){};
    public void draw_a_circle(){};
}

ShapeDrawingSingleton shapedrawingSingleton=new ShapeDrawingSingleton(new DP1ShapeDrawing());

V1Circle v1circle=new V1Circle();
v1circle.draw();

//其他的类��g��上面�?/span>

TiGERTiAN 2007-04-08 14:27 发表评论

Strategy Pattern

TiGERTiAN — Sat, 07 Apr 2007 09:23:00 GMT

�?Strategy Pattern中，当一个�Q务控制器需要处理某��事物的时候，它可以命令他所控制的事务读取一个configuration file�Q�然后根据这个file��一些配�|�信息传递给一个接口从而调用相应的信息�Q�而这个接口可能是一个Aggregation的接口，�q�个Aggregation可能是一�l�规则或者内容不一��P��但具有相同的�c�d��或者特点的事务�Q�可以用一个Abstract class让他们��承，
�q�样�l�一��对象交�l�固定接口，而外部只要调用这个接口即可�?br>以下�?#8220;四�h�?#8221;的说法�?br>

Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.[6]

public class TaskController {
  public void process () {
     // this code is an emulation of a
     // processing task controller
     // . . .
     // figure out which country you are in
     CalcTax myTax;
     myTax= getTaxRulesForUS();
     SalesOrder mySO= new SalesOrder();
     mySO.process( myTax);// 当然你还可以让myTax=getTaxRulesForCan();�q�样mySo.process(myTax)��׃��(x��)按照加拿大的�E�率处理
  }
  private CalcTax getTaxRulesForUS() {
     // In real life, get the tax rules based on
     // country you are in.  You may have the
     // logic here or you may have it in a
     // configuration file
     // Here, just return a USTax so this
     // will compile.
     return new USTax();
  }
}

public class SalesOrder {
   public void process (CalcTax taxToUse) {
      long itemNumber= 0;
      double price= 0;

      // given the tax object to use

      // . . .

      // calculate tax
      double tax=
         taxToUse.taxAmount( itemNumber, price);
   }
}

public abstract class CalcTax {
   abstract public double taxAmount(
      long itemSold, double price);
}

public class CanTax extends CalcTax {
   public double taxAmount(
      long itemSold, double price) {
      // in real life, figure out tax according to
      // the rules in Canada and return it
      // here, return 0 so this will compile
      return 0.0;
   }
}
public class USTax extends CalcTax {
   public double taxAmount(
      long itemSold, double price) {
      // in real life, figure out tax according to
      // the rules in the US and return it
      // here, return 0 so this will compile
      return 0.0;
   }
}

实际整个Strategy的核�?j��)部分就是抽象类的��?使用Strategy模式可以在用户需要变化时,修改量很��?而且快�?

Strategy和Factory有一定的�c�M��,Strategy相对��单容易理�?�q�且可以在运行时刻自由切换。Factory重点是用来创建对象�?/p>

Strategy适合下列场合:

1.以不同的格式保存文�g;

2.以不同的��法压羃文�g;

3.以不同的��法截获图象;

4.以不同的格式输出同样数据的图�?比如曲线或框图bar�{?/p>

TiGERTiAN 2007-04-07 17:23 发表评论

Facade Pattern

TiGERTiAN — Thu, 05 Apr 2007 14:40:00 GMT

如果有一个很复杂的系�l�，但你只想用里面的一部分功能�Q�怎么办？
用Facade Pattern思想�Q�把一些复杂的功能模块分分清楚�Q�然后重新写一个功能接口来�l�织你想要的�q�些功能�Q�这样就可以很方便的�q�行调用�Q�如此方便清楚，何乐而不为呢�Q�嘿�?/p>

TiGERTiAN 2007-04-05 22:40 发表评论

Adapter Pattern

TiGERTiAN — Thu, 05 Apr 2007 14:32:00 GMT

class Circle extends Shape {

private XXCircle myXXCircle;

public Circle () {
myXXCircle= new XXCircle();
}

void public display() {
myXXCircle.displayIt();
}

}

某�h写了(ji��n)一个XXCircle�c�，和我��要写的Circle�c�d��能相同，但他没有�l�承Shape�c�，我如何��用它的类而不用重写呢�Q�试用Adapter Pattern�Q�如上所�C�，��他的方法变为我的Circle�cȝ��一个成员变量，�q�样��尽可以调用它的�Ҏ(gu��)��?ji��n)。。哈�?

TiGERTiAN 2007-04-05 22:32 发表评论