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Adapter Pattern in Design Pattern

适配器模式

Overview

适配器模式(Adapter Pattern)是作为两个不兼容的接口之间的桥梁。

这种类型的设计模式属于结构型模式,它结合了两个独立接口的功能。

这种模式涉及到一个单一的类,该类负责加入独立的或不兼容的接口功能。

主要解决

主要解决在软件系统中,常常要将一些”现存的对象”放到新的环境中,而新环境要求的接口是现对象不能满足的。

何时使用

  • 系统需要使用现有的类,而此类的接口不符合系统的需要。
  • 想要建立一个可以重复使用的类,用于与一些彼此之间没有太大关联的一些类,包括一些可能在将来引进的类一起工作,这些源类不一定有一致的接口。
  • 通过接口转换,将一个类插入另一个类系中。(比如老虎和飞禽,现在多了一个飞虎,在不增加实体的需求下,增加一个适配器,在里面包容一个虎对象,实现飞的接口。)

应用实例

  • 美国电器 110V,中国 220V,就要有一个适配器将 110V 转化为 220V
  • 在 LINUX 上运行 WINDOWS 程序
  • Java中JDBC

优点

  • 可以让任何两个没有关联的类一起运行
  • 提高了类的复用
  • 增加了类的透明度
  • 灵活性好

实现

Adapter Pattern

Player Interface

Media Player

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public interface MediaPlayer {
/**
* play a media resource
* @param audioType audio type
* @param filename file name
*/
void play(String audioType, String filename);
}

Advanced Media Player

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public interface AdvancedMediaPlayer {
/**
* play a vlc resource
*
* @param filename file name
*/
void playVlc(String filename);

/**
* play a mp4 resource
*
* @param filename file name
*/
void playMp4(String filename);
}

Player Implementation

MP4 Player

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public class Mp4Player implements AdvancedMediaPlayer {
@Override
public void playVlc(String filename) {

}

@Override
public void playMp4(String filename) {
System.out.println("Mp4Player.playMp4");
}
}

VLC Player

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public class VlcPlayer implements AdvancedMediaPlayer {
@Override
public void playVlc(String filename) {
System.out.println("VlcPlayer.playVlc");
}

@Override
public void playMp4(String filename) {

}
}

Adapter

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public class MediaAdapter implements MediaPlayer {

public AdvancedMediaPlayer advancedMediaPlayer;

public MediaAdapter(String audioType) {
audioType = audioType.toLowerCase();
switch (audioType) {
case "vlc":
advancedMediaPlayer = new VlcPlayer();
break;
case "mp4":
advancedMediaPlayer = new Mp4Player();
break;
default:
break;
}
}

@Override
public void play(String audioType, String filename) {
audioType = audioType.toLowerCase();
switch (audioType) {
case "vlc":
advancedMediaPlayer.playVlc(filename);
break;
case "mp4":
advancedMediaPlayer.playMp4(filename);
break;
default:
break;
}
}
}

Audio Player

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public class AudioPlayer implements MediaPlayer {

public MediaPlayer mediaAdapter;

@Override
public void play(String audioType, String filename) {
audioType = audioType.toLowerCase();
switch (audioType) {
case "mp3":
System.out.println("AudioPlayer.play: MP3 is playing.");
break;
case "vlc":
case "mp4":
mediaAdapter = new MediaAdapter(audioType);
mediaAdapter.play(audioType, filename);
break;
default:
System.out.println("AudioPlayer.play: Invalid Media [ " + audioType + " ], the format is not supported.");
break;
}
}
}

Tester

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package individual.cy.learn.pattern.structural.adapter;

/**
* @author mystic
*/
public class AdapterPatternTester {
public static void main(String[] args) {
AudioPlayer audioPlayer = new AudioPlayer();

audioPlayer.play("mp3", "beyond the horizon.mp3");
audioPlayer.play("mp4", "alone.mp4");
audioPlayer.play("vlc", "far far away.vlc");
audioPlayer.play("avi", "mind me.avi");

}
}

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AudioPlayer.play: MP3 is playing.
Mp4Player.playMp4
VlcPlayer.playVlc
AudioPlayer.play: Invalid Media [ avi ], the format is not supported.