Realization

1// Interface defining the contract
2public interface Notifier {
3    void send(String message, String recipient);
4    boolean isAvailable();
5}
6
7// Realization: EmailNotifier realizes Notifier
8public class EmailNotifier implements Notifier {
9    private String smtpServer;
10    
11    public EmailNotifier(String smtpServer) {
12        this.smtpServer = smtpServer;
13    }
14    
15    @Override
16    public void send(String message, String recipient) {
17        System.out.println("Sending email to " + recipient + ": " + message);
18        // Email-specific implementation
19    }
20    
21    @Override
22    public boolean isAvailable() {
23        return smtpServer != null && !smtpServer.isEmpty();
24    }
25}
26
27// Realization: SMSNotifier realizes Notifier
28public class SMSNotifier implements Notifier {
29    private String apiKey;
30    
31    public SMSNotifier(String apiKey) {
32        this.apiKey = apiKey;
33    }
34    
35    @Override
36    public void send(String message, String recipient) {
37        System.out.println("Sending SMS to " + recipient + ": " + message);
38        // SMS-specific implementation
39    }
40    
41    @Override
42    public boolean isAvailable() {
43        return apiKey != null && !apiKey.isEmpty();
44    }
45}
46
47// Realization: PushNotifier realizes Notifier
48public class PushNotifier implements Notifier {
49    @Override
50    public void send(String message, String recipient) {
51        System.out.println("Sending push notification to " + recipient);
52    }
53    
54    @Override
55    public boolean isAvailable() {
56        return true;
57    }
58}
59
60// Client works with interface
61public class NotificationService {
62    private List<Notifier> notifiers;
63    
64    public NotificationService() {
65        this.notifiers = new ArrayList<>();
66    }
67    
68    public void addNotifier(Notifier notifier) {
69        notifiers.add(notifier);
70    }
71    
72    public void notifyAll(String message, String recipient) {
73        for (Notifier notifier : notifiers) {
74            if (notifier.isAvailable()) {
75                notifier.send(message, recipient);
76            }
77        }
78    }
79}
80
81// Usage
82public class Main {
83    public static void main(String[] args) {
84        NotificationService service = new NotificationService();
85        
86        // All realizations of Notifier interface
87        service.addNotifier(new EmailNotifier("smtp.example.com"));
88        service.addNotifier(new SMSNotifier("api-key-123"));
89        service.addNotifier(new PushNotifier());
90        
91        service.notifyAll("Hello!", "user@example.com");
92    }
93}