observer example

import java.util.ArrayList;
import java.util.List;

class Subject<Tp> {
    private Tp state;
    private List<Observer> observers;

    public Subject() {
        observers = new ArrayList<>();
    }

    public Tp getState() {
        return state;
    }

    public void setState(Tp state) {
        this.state = state;
        notifyAllObs();
    }

    public void registerObs(Observer observer) {
        observers.add(observer);
    }

    private void notifyAllObs() {
        for (Observer observer : observers) {
            observer.update();
        }
    }
}

abstract class Observer {
    public Observer(Subject subject) {
        this.subject = subject;
        this.subject.registerObs(this);
    }

    protected Subject subject;
    public abstract void update();
}
//end obs pattern

class Message {
    public String to, title, content;

    public Message(String to, String title, String content) {
        this.to = to;
        this.title = title;
        this.content = content;
    }

    @Override
    public String toString() {
        return "Message{" +
                "to='" + to + '\'' +
                ", title='" + title + '\'' +
                ", content='" + content + '\'' +
                '}';
    }
}

class MailObserver extends Observer {

    public MailObserver(Subject subject) {
        super(subject);
    }

    @Override
    public void update() {
        System.out.println("Mail sent! " + subject.getState().toString());
    }
}

class SmsObserver extends Observer {

    public SmsObserver(Subject subject) {
        super(subject);
    }

    @Override
    public void update() {
        System.out.println("Sms sent! " + subject.getState().toString());
    }
}//*/

public class Main {

    public static void main(String[] args) {
        var subject = new Subject<Message>();

        new MailObserver(subject);
        new SmsObserver(subject);

        subject.setState(new Message("andrew", "hi", "wyd?"));
    }
}