设计模式之适配器模式

Adapter Design Pattern

definition Convert the interface of a class into another interface clients expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces. Frequency of use:   medium high

UML class diagram

participants

    The classes and/or objects participating in this pattern are:

• Target   (ChemicalCompound)
  • defines the domain-specific interface that Client uses.
• Adapter   (Compound)
  • adapts the interface Adaptee to the Target interface.
• Adaptee   (ChemicalDatabank)
  • defines an existing interface that needs adapting.
• Client   (AdapterApp)
  • collaborates with objects conforming to the Target interface.

sample code in C#

This structural code demonstrates the Adapter pattern which maps the interface of one class onto another so that they can work together. These incompatible classes may come from different libraries or frameworks.

// Adapter pattern -- Structural example

using System; namespace DoFactory.GangOfFour.Adapter.Structural {    // Mainapp test application    class MainApp   {      static void Main()     {        // Create adapter and place a request       Target target = new Adapter();       target.Request();        // Wait for user       Console.Read();     }   }    // "Target"    class Target   {      public virtual void Request()     {       Console.WriteLine("Called Target Request()");     }   }    // "Adapter"    class Adapter : Target   {      private Adaptee adaptee = new Adaptee();      public override void Request()     {        // Possibly do some other work        // and then call SpecificRequest       adaptee.SpecificRequest();     }   }    // "Adaptee"    class Adaptee   {      public void SpecificRequest()     {       Console.WriteLine("Called SpecificRequest()");     }   } }

Output Called SpecificRequest()

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This real-world code demonstrates the use of a legacy chemical databank. Chemical compound objects access the databank through an Adapter interface.

// Adapter pattern -- Real World example

using System; namespace DoFactory.GangOfFour.Adapter.RealWorld {    // MainApp test application    class MainApp   {      static void Main()     {        // Non-adapted chemical compound       Compound stuff = new Compound("Unknown");       stuff.Display();               // Adapted chemical compounds       Compound water = new RichCompound("Water");       water.Display();       Compound benzene = new RichCompound("Benzene");       benzene.Display();       Compound alcohol = new RichCompound("Alcohol");       alcohol.Display();        // Wait for user       Console.Read();     }   }    // "Target"    class Compound   {      protected string name;      protected float boilingPoint;      protected float meltingPoint;      protected double molecularWeight;      protected string molecularFormula;      // Constructor      public Compound( string name)     {        this.name = name;     }      public virtual void Display()     {       Console.WriteLine("/nCompound: {0} ------ ", name);     }   }    // "Adapter"    class RichCompound : Compound   {      private ChemicalDatabank bank;      // Constructor      public RichCompound( string name) : base(name)     {     }      public override void Display()     {        // Adaptee       bank = new ChemicalDatabank();       boilingPoint = bank.GetCriticalPoint(name, "B");       meltingPoint = bank.GetCriticalPoint(name, "M");       molecularWeight = bank.GetMolecularWeight(name);       molecularFormula = bank.GetMolecularStructure(name);        base.Display();       Console.WriteLine(" Formula: {0}", molecularFormula);       Console.WriteLine(" Weight : {0}", molecularWeight);       Console.WriteLine(" Melting Pt: {0}", meltingPoint);       Console.WriteLine(" Boiling Pt: {0}", boilingPoint);     }   }    // "Adaptee"    class ChemicalDatabank   {      // The Databank 'legacy API'      public float GetCriticalPoint( string compound, string point)     {        float temperature = 0.0F;        // Melting Point        if (point == "M")       {          switch (compound.ToLower())         {            case "water" : temperature = 0.0F; break;            case "benzene" : temperature = 5.5F; break;            case "alcohol" : temperature = -114.1F; break;         }       }        // Boiling Point        else       {          switch (compound.ToLower())         {            case "water" : temperature = 100.0F; break;            case "benzene" : temperature = 80.1F; break;            case "alcohol" : temperature = 78.3F; break;         }       }        return temperature;     }      public string GetMolecularStructure( string compound)     {        string structure = "";        switch (compound.ToLower())       {          case "water" : structure = "H20"; break;          case "benzene" : structure = "C6H6"; break;          case "alcohol" : structure = "C2H6O2"; break;       }        return structure;     }      public double GetMolecularWeight( string compound)     {        double weight = 0.0;        switch (compound.ToLower())       {          case "water" : weight = 18.015; break;          case "benzene" : weight = 78.1134; break;          case "alcohol" : weight = 46.0688; break;       }        return weight;     }   } }

Output Compound: Unknown ------ Compound: Water ------  Formula: H20  Weight : 18.015  Melting Pt: 0  Boiling Pt: 100 Compound: Benzene ------  Formula: C6H6  Weight : 78.1134  Melting Pt: 5.5  Boiling Pt: 80.1 Compound: Alcohol ------  Formula: C2H6O2  Weight : 46.0688  Melting Pt: -114.1  Boiling Pt: 78.3