Adapter Pattern in Design Pattern

Posted on In Views:
Let's begin to learn what's Adapter 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

1
2
3
4
5
6
7
8
9
10
11
12
13
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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");

    }
}
1
2
3
4
AudioPlayer.play: MP3 is playing.
Mp4Player.playMp4
VlcPlayer.playVlc
AudioPlayer.play: Invalid Media [ avi ], the format is not supported.