Adapter

// ── OBJECT ADAPTER (preferred — uses composition) ──────────────────

// Target — what the client expects
public interface MediaPlayer {
    void play(String filename);
}

// Adaptee — existing class with incompatible interface
public class VLCPlayer {
    public void playVLC(String file) {
        System.out.println("VLC playing: " + file);
    }
}
public class MP4Player {
    public void playMP4(String file) {
        System.out.println("MP4 playing: " + file);
    }
}

// Adapter — wraps adaptee, exposes Target interface
public class MediaAdapter implements MediaPlayer {
    private VLCPlayer vlc;
    private MP4Player mp4;

    public MediaAdapter(String type) {
        if (type.equals("vlc"))  vlc = new VLCPlayer();
        if (type.equals("mp4"))  mp4 = new MP4Player();
    }

    public void play(String filename) {
        if (vlc != null) vlc.playVLC(filename);
        if (mp4 != null) mp4.playMP4(filename);
    }
}

// Client — only knows MediaPlayer
public class AudioPlayer implements MediaPlayer {
    public void play(String filename) {
        String ext = filename.substring(filename.lastIndexOf('.') + 1);
        if (ext.equals("mp3")) {
            System.out.println("Playing MP3: " + filename);
        } else if (ext.equals("vlc") || ext.equals("mp4")) {
            new MediaAdapter(ext).play(filename); // delegates via adapter
        } else {
            System.out.println("Unsupported format");
        }
    }
}

// ── CLASS ADAPTER (uses multiple inheritance — Java: extend + implement) ─
public class ClassAdapter extends VLCPlayer implements MediaPlayer {
    public void play(String filename) {
        playVLC(filename); // inherited from VLCPlayer directly
    }
}

// Client usage
AudioPlayer player = new AudioPlayer();
player.play("song.mp3");
player.play("movie.vlc");
player.play("video.mp4");

// ❌ BREAKING — leaking the adaptee
public class LeakyAdapter implements MediaPlayer {
    private VLCPlayer vlc = new VLCPlayer();
    public VLCPlayer getVLC() { return vlc; } // ❌ exposes internals
    public void play(String f) { vlc.playVLC(f); }
}
// Client now calls getVLC().playVLC() — adapter is useless

// ✅ FIX — no getter, adaptee strictly private
public class SafeAdapter implements MediaPlayer {
    private final VLCPlayer vlc; // private, final, no getter
    public SafeAdapter(VLCPlayer vlc) { this.vlc = vlc; }
    public void play(String f) { vlc.playVLC(f); }
}

// ❌ BREAKING — silent no-op on unimplemented method
public class BrokenAdapter implements MediaPlayer {
    public void play(String f)   { /* TODO — nothing happens! */ }
}

// ✅ FIX — fail fast with UnsupportedOperationException
public void play(String f) {
    throw new UnsupportedOperationException(
        "play() not supported by this adapter");
}