本专栏将从基础开始，循序渐进，由浅入深讲解常见的设计模式，希望大家都能够从中有所收获，也请大家多多支持。
专栏地址:设计模式实战
所有代码地址:代码地址
如果文章知识点有错误的地方，请指正！大家一起学习，一起进步。

1 适配器模式

适配器模式：使用另一个类将接口根据不同类型实例化成不同类，使用一个类进行封装，需要什么类型就适配什么类型，然后执行对应的方法。本章通过以下例子来演示适配器模式的使用，UML图如下：

在这个例子中，AdvancedMediaPlayer接口有两个抽象函数，分别是playVlc()和playMp4。AdvancedMediaPlayer接口有两个实现类VlcPlayer和Mp4Player，VlcPlayer类实现了playVlc函数()，Mp4Player类实现了playMp4()。MediaAdapter类和AudioPlayer类实现了接口MedeiaPlayer的play()函数，MediaAdaper适配器中中含有接口AdvancedMediaPlayer类的对象，该类的构造函数会根据不同类型实例化AdvancedMediaPlayer，在AudioPlayer类中含有适配器对象mediaAdapter,当AudioPlayer调用play方法时会给适配器MediaAdaper传递不同的参数，适配器根据不同的参数调用不同的实例方法。

• MediaPlayer.java

public interface MediaPlayer {
    
    
   public void play(String audioType, String fileName);
}

• AdvancedMediaPlayer.java

public interface AdvancedMediaPlayer {
    
    	
   public void playVlc(String fileName);
   public void playMp4(String fileName);
}

• VlcPlayer.java

public class VlcPlayer implements AdvancedMediaPlayer{
    
    
   @Override
   public void playVlc(String fileName) {
    
    
      System.out.println("Playing vlc file. Name: "+ fileName);		
   }

   @Override
   public void playMp4(String fileName) {
    
    
      //do nothing
   }
}

• Mp4Player.java

public class Mp4Player implements AdvancedMediaPlayer{
    
    

   @Override
   public void playVlc(String fileName) {
    
    
      //do nothing
   }

   @Override
   public void playMp4(String fileName) {
    
    
      System.out.println("Playing mp4 file. Name: "+ fileName);		
   }
}

• MediaAdapter.java

public class MediaAdapter implements MediaPlayer {
    
    

   AdvancedMediaPlayer advancedMusicPlayer;

   public MediaAdapter(String audioType){
    
    
   
      if(audioType.equalsIgnoreCase("vlc") ){
    
    
         advancedMusicPlayer = new VlcPlayer();			
         
      }else if (audioType.equalsIgnoreCase("mp4")){
    
    
         advancedMusicPlayer = new Mp4Player();
      }	
   }

   @Override
   public void play(String audioType, String fileName) {
    
    
   
      if(audioType.equalsIgnoreCase("vlc")){
    
    
         advancedMusicPlayer.playVlc(fileName);
      }
      else if(audioType.equalsIgnoreCase("mp4")){
    
    
         advancedMusicPlayer.playMp4(fileName);
      }
   }
}

• AudioPlayer.java

public class AudioPlayer implements MediaPlayer {
    
    
   MediaAdapter mediaAdapter; 

   @Override
   public void play(String audioType, String fileName) {
    
    		

      //inbuilt support to play mp3 music files
      if(audioType.equalsIgnoreCase("mp3")){
    
    
         System.out.println("Playing mp3 file. Name: " + fileName);			
      } 
      
      //mediaAdapter is providing support to play other file formats
      else if(audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")){
    
    
         mediaAdapter = new MediaAdapter(audioType);
         mediaAdapter.play(audioType, fileName);
      }
      
      else{
    
    
         System.out.println("Invalid media. " + audioType + " format not supported");
      }
   }   
}

• AdapterPatternDemo.java

package com.cgw;

public class AdapterPatternDemo {
    
    
    public static void main(String[] args) {
    
    
        AudioPlayer audioPlayer = new AudioPlayer();

        audioPlayer.play("mp3", "media1.mp3");
        audioPlayer.play("mp4", "media2.mp4");
        audioPlayer.play("vlc", "media3.vlc");
        audioPlayer.play("avi", "media4.avi");
    }
}

输出结果：

Playing mp3 file. Name: beyond the horizon.mp3
Playing mp4 file. Name: alone.mp4
Playing vlc file. Name: far far away.vlc
Invalid media. avi format not supported

2 桥接模式（以组合代替继承，把需要桥接的对象放入抽象类中）

public class BridgeTest
{
    
    
    public static void main(String[] args)
    {
    
    
        Implementor imple=new ConcreteImplementorA();
        Abstraction abs=new RefinedAbstraction(imple);
        abs.Operation(); 
    }
}
//实现化角色
interface Implementor
{
    
    
    public void OperationImpl();
}
//具体实现化角色
class ConcreteImplementorA implements Implementor
{
    
    
    public void OperationImpl()
    {
    
    
        System.out.println("具体实现化(Concrete Implementor)角色被访问" );
    }
}
//抽象化角色
abstract class Abstraction
{
    
    
    protected Implementor imple;
    protected Abstraction(Implementor imple)
    {
    
    
        this.imple=imple;
    }
    public void Operation(){
    
    
        imple.OperationImpl();
    }
}
//扩展抽象化角色
class RefinedAbstraction extends Abstraction
{
    
    
    protected RefinedAbstraction(Implementor imple)
    {
    
    
        super(imple);
    }
    public void Operation()
    {
    
    
        System.out.println("扩展抽象化(Refined Abstraction)角色被访问" );
        super.Operation();
    }
}