Figure 15 shows a first example of content-based publish/subscribe. We suppose here that Bob is only interested in what a particular participant, Alice, publishes on topic /Chat/Insomnia. Bob defines a corresponding condition. The null argument in the condition initialization denotes a set of empty argument lists. A subscription is viewed as an interest in future elements, and is expressed by a call to the contains() method.
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/* connect */
DASet myChat = new DAStrongSet("/Chat/Insomnia");
/* create condition */
Condition onlyAlice =
new Equals("/getSender", null, "Alice");
/* create callback object and subscribe */
Notifiable n = new ChatNotifiable();
myChat.contains(n, onlyAlice);
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