23种设计模式 UML 类图及对应示例代码 (三)

21.DoFactory.GangOfFour.Strategy.Structural

　　Strategy：定义一系列的算法，把他们封装起来，并可以相互替换，使算法独立于客户。

策略模式：策略模式针对一组算法，将每一个算法封装到具有共同接口的独立的类中，从而使得它们可以相互替换。策略模式使得算法可以在不影响到客户端的情况下发生变化。策略模式把行为和环境分开。环境类负责维持和查询行为类，各种算法在具体的策略类中提供。由于算法和环境独立开来，算法的增减，修改都不会影响到环境和客户端。

Code
using System;
using System.Collections;

namespace DoFactory.GangOfFour.Visitor.Structural
{
/// <summary>
/// MainApp startup class for Structural
/// Visitor Design Pattern.
/// </summary>
class MainApp
{
static void Main()
{
// Setup structure
ObjectStructure o = new ObjectStructure();
o.Attach(new ConcreteElementA());
o.Attach(new ConcreteElementB());

// Create visitor objects
ConcreteVisitor1 v1 = new ConcreteVisitor1();
ConcreteVisitor2 v2 = new ConcreteVisitor2();

// Structure accepting visitors
o.Accept(v1);
o.Accept(v2);

// Wait for user
Console.Read();
}
}

// "Visitor"

abstract class Visitor
{
public abstract void VisitConcreteElementA(
ConcreteElementA concreteElementA);
public abstract void VisitConcreteElementB(
ConcreteElementB concreteElementB);
}

// "ConcreteVisitor1"

class ConcreteVisitor1 : Visitor
{
public override void VisitConcreteElementA(
ConcreteElementA concreteElementA)
{
Console.WriteLine("{0} visited by {1}",
concreteElementA.GetType().Name, this.GetType().Name);
}

public override void VisitConcreteElementB(
ConcreteElementB concreteElementB)
{
Console.WriteLine("{0} visited by {1}",
concreteElementB.GetType().Name, this.GetType().Name);
}
}

// "ConcreteVisitor2"

class ConcreteVisitor2 : Visitor
{
public override void VisitConcreteElementA(
ConcreteElementA concreteElementA)
{
Console.WriteLine("{0} visited by {1}",
concreteElementA.GetType().Name, this.GetType().Name);
}

public override void VisitConcreteElementB(
ConcreteElementB concreteElementB)
{
Console.WriteLine("{0} visited by {1}",
concreteElementB.GetType().Name, this.GetType().Name);
}
}

// "Element"

abstract class Element
{
public abstract void Accept(Visitor visitor);
}

// "ConcreteElementA"

class ConcreteElementA : Element
{
public override void Accept(Visitor visitor)
{
visitor.VisitConcreteElementA(this);
}

public void OperationA()
{
}
}

// "ConcreteElementB"

class ConcreteElementB : Element
{
public override void Accept(Visitor visitor)
{
visitor.VisitConcreteElementB(this);
}

public void OperationB()
{
}
}

// "ObjectStructure"

class ObjectStructure
{
private ArrayList elements = new ArrayList();

public void Attach(Element element)
{
elements.Add(element);
}

public void Detach(Element element)
{
elements.Remove(element);
}

public void Accept(Visitor visitor)
{
foreach (Element e in elements)
{
e.Accept(visitor);
}
}
}
}

设计原则及分类介绍:

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