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public interface Observer {
    void update(String message);
}

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@AllArgsConstructor
public static class WeiXinUser implements Observer {
    private final String name;
    public void update(String message) {
        System.out.println(name + "观察到-" + message);
    }
}

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public interface Subject {
    void attach(Observer observer);
    void detach(Observer observer);
    void notify(String message);
}

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public static class SubscriptionSubject implements Subject {
    private final List<Observer> weiXinUserList = new ArrayList<>();
    @Override
    public void attach(Observer observer) {
        weiXinUserList.add(observer);
    }
    @Override
    public void detach(Observer observer) {
        weiXinUserList.remove(observer);
    }
    @Override
    public void notify(String message) {
        for (Observer observer : weiXinUserList) {
            observer.update(message);
        }
    }
}

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SubscriptionSubject subject = new SubscriptionSubject();
subject.attach(new WeiXinUser("孙悟空"));
subject.attach(new WeiXinUser("猪悟能"));
subject.attach(new WeiXinUser("沙悟净"));
subject.notify("师父被抓走了！！！");

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孙悟空观察到-师父被抓走了！！！
猪悟能观察到-师父被抓走了！！！
沙悟净观察到-师父被抓走了！！！