设计模式—适配器模式

介绍

代码

接口

定义媒体播放器接口 MediaPlayer，其中 play 方法用于播放媒体文件

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

定义高级播放器接口 AdvancedMediaPlayer，规定指定类型媒体的播放方法

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

    public void playMp4(String fileName);
}

适配器类

引入适配器类 MediaAdapter，实现 MediaPlayer 接口， 包含成员 AdvancedMediaPlayer。这样在调用 MediaPlayer 的 play 方法的时候，可以转接到 AdvancedMediaPlayer 的 playVlc 方法和 playMp4 方法，这就是适配器类的作用：表面上 A 类的行为，用户不知道调用的实际是 B 类，也就是适配器类完成了两个类行为的对接

public class MediaAdapter implements MediaPlayer {
    AdvancedMediaPlayer advancedMediaPlayer;

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

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

实体类

实体类 AudioPlayer 实现 MediaPlayer 接口

public class AudioPlayer implements MediaPlayer {
    MediaPlayer mediaPlayer;

    @Override
    public void play(String audioType, String fileName) {
        if(audioType.equalsIgnoreCase("mp3")){
            System.out.println("Playing mp3 file. Name: " + fileName);
        } else if(audioType.equalsIgnoreCase("vlc") || audioType.equalsIgnoreCase("mp4")) {
            mediaPlayer = new MediaAdapter(audioType);
            mediaPlayer.play(audioType, fileName);
        }else{
            System.out.println("Invalid media.");
        }
    }
}

AdvancedMediaPlayer 接口的两个实现类 Mp4Player、VlcPlayer

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);
    }
}

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
    }
}

测试

public class AdapterTest {
    @Test
    void test() {
        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");
    }
}