Java设计模式——适配器模式

适配器模式充当两个不兼容接口之间的桥梁， 它属于结构模式。
它涉及一个单一的类，负责连接独立或不兼容的接口功能。比如读卡器，它充当存储卡和电脑之间的适配器。我们将存储卡插入读卡器并将读卡器插入电脑，这样就可以通过电脑读取存储卡内容。

下面进行演示说明。
需求：假设我们有一台MP3播放器，但我们又希望它能播放vlc和mp4文件。
步骤：
1、创建接口MediaPlayer（媒体播放），以及一个实现类AudioPlayer（音频播放）
2、创建另外一个接口AdvancedMediaPlayer（高级媒体播放器），以及它的实现类（VLCPlayer、Mp4Player）
3、我们想让 AudioPlayer也能播放vlc和mp4。创建一个适配器类MediaAdapter，它实现了MediaPlayer接口，并使用 AdvancedMediaPlayer对象来播放所需的格式。
4、AudioPlayer 使用适配器类 MediaAdapter，并将媒体文件传递给它，并不需知道实际文件类型。

1、创建接口MediaPlayer、AdvancedMediaPlayer

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public interface MediaPlayer {    public void play(String audioType, String fileName); }   public interface AdvancedMediaPlayer {     public void playVlc(String fileName);    public void playMp4(String fileName); }

2、创建AdvancedMediaPlayer的实现类

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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    } }   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);        } }

3、创建适配器类MediaAdapter，实现接口MediaPlayer

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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);       }    } }

4、创建AudioPlayer类，实现接口MediaPlayer

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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");       }    }   }

5、测试

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public class AdapterPatternDemo {    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");    } }

6、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