OBSERVER PATTERN
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In software engineering, the mediator pattern defines an object that encapsulates how a set of objects interact. This pattern is considered to be a behavioral pattern due to the way it can alter the program's running behavior. In object-oriented programming, programs often consist of many classes. Business logic and computation are distributed among these classes. However, as more classes are added to a program, especially during maintenance and/or refactoring, the problem of communication between these classes may become more complex. This makes the program harder to read and maintain. Furthermore, it can become difficult to change the program, since any change may affect code in several other classes. With the mediator pattern, communication between objects is encapsulated within a mediator object. Objects no longer communicate directly with each other, but instead communicate through the mediator. This reduces the dependencies between communicating objects, thereby reducing coupling.
In connection with: Mediator pattern
Title combos: Mediator pattern
Description combos: objects pattern classes these affect pattern program an the
In software design and software engineering, the observer pattern is a software design pattern in which an object, called the subject (also known as event source or event stream), maintains a list of its dependents, called observers (also known as event sinks), and automatically notifies them of any state changes, typically by calling one of their methods. The subject knows its observers through a standardized interface and manages the subscription list directly. This pattern creates a one-to-many dependency where multiple observers can listen to a single subject, but the coupling is typically synchronous and direct—the subject calls observer methods when changes occur, though asynchronous implementations using event queues are possible. Unlike the publish-subscribe pattern, there is no intermediary broker; the subject and observers have direct references to each other. It is commonly used to implement event handling systems in event-driven programming, particularly in-process systems like GUI toolkits or MVC frameworks. This makes the pattern well-suited to processing data that arrives unpredictably—such as user input, HTTP requests, GPIO signals, updates from distributed databases, or changes in a GUI model.
In connection with: Observer pattern
Title combos: Observer pattern
Description combos: queues observer single databases when handling distributed the systems
An observer is one who engages in observation or in watching an experiment. Observer may also refer to:
In connection with: Observer
Description combos: Observer watching who is experiment an experiment observer is
In software engineering, behavioral design patterns are design patterns that identify common communication patterns among objects. By doing so, these patterns increase flexibility in carrying out communication.
In connection with: Behavioral pattern
Title combos: Behavioral pattern
Description combos: identify communication in communication behavioral in In software so
In software architecture, the publish–subscribe pattern (pub/sub) is a messaging pattern in which message senders, called publishers, categorize messages into classes (or topics), and send them without needing to know which components will receive them. Message recipients, called subscribers, express interest in one or more classes and only receive messages in those classes, without needing to know the identity of the publishers. This pattern decouples the components that produce messages from those that consume them, and supports asynchronous, many-to-many communication. The publish–subscribe model is commonly contrasted with message queue-based and point-to-point messaging models, where producers send messages directly to consumers. Publish–subscribe is a sibling of the message queue paradigm, and is typically a component of larger message-oriented middleware systems. Many modern messaging frameworks and protocols, such as the Java Message Service (JMS), Apache Kafka, and MQTT, support both the pub/sub and queue-based models. This pattern provides greater network scalability and supports more dynamic topologies, but can make it harder to modify the publisher’s logic or the structure of the published data. Compared to synchronous patterns like RPC and point-to-point messaging, publish–subscribe provides the highest level of decoupling among architectural components. However, it can also lead to semantic or format coupling between publishers and subscribers, which may cause systems to become entangled or brittle over time.
In connection with: Publish–subscribe pattern
Title combos: pattern subscribe Publish subscribe pattern
Description combos: to subscribers architectural with in supports to the of
In computing, reactive programming is a declarative programming paradigm concerned with data streams and the propagation of change. With this paradigm, it is possible to express static (e.g., arrays) or dynamic (e.g., event emitters) data streams with ease, and also communicate that an inferred dependency within the associated execution model exists, which facilitates the automatic propagation of the changed data flow. For example, in an imperative programming setting, a := b + c would mean that a is being assigned the result of b + c at the instant the expression is evaluated, and later, the values of b and c can be changed with no effect on the value of a. On the other hand, in reactive programming, the value of a is automatically updated whenever the values of b or c change, without the program having to explicitly re-state the statement a := b + c to re-assign the value of a. Another example is a hardware description language such as Verilog, where reactive programming enables changes to be modeled as they propagate through circuits. Reactive programming has been proposed as a way to simplify the creation of interactive user interfaces and near-real-time system animation. For example, in a model–view–controller (MVC) architecture, reactive programming can facilitate changes in an underlying model being reflected automatically in an associated view.
In connection with: Reactive programming
Title combos: programming Reactive
Description combos: changes static of to with programming setting effect mean
In computer programming, the lapsed listener problem is a common source of memory leaks for object-oriented programming languages, among the most common ones for garbage collected languages. It originates in the observer pattern, where observers (or listeners) register with a subject (or publisher) to receive events. In basic implementation, this requires both explicit registration and explicit deregistration, as in the dispose pattern, because the subject holds strong references to the observers, keeping them alive. The leak happens when an observer fails to unsubscribe from the subject when it no longer needs to listen. Consequently, the subject still holds a reference to the observer which prevents it from being garbage collected — including all other objects it is referring to — for as long as the subject is alive, which could be until the end of the application. This causes not only a memory leak, but also a performance degradation with an "uninterested" observer receiving and acting on unwanted events. This can be prevented by the subject holding weak references to the observers, allowing them to be garbage collected as normal without needing to be unregistered.
In connection with: Lapsed listener problem
Title combos: problem listener Lapsed listener problem
Description combos: this references end most the computer prevented the other
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