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Observer Design Pattern
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, particu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software Design
Software design is the process of conceptualizing how a software system will work before it is implemented or modified. Software design also refers to the direct result of the design process the concepts of how the software will work which consists of both design documentation and undocumented concepts. Software design usually is directed by goals for the resulting system and involves problem-solving and planning including both high-level software architecture and low-level component and algorithm design. In terms of the waterfall development process, software design is the activity of following requirements specification and before coding. General process The design process enables a designer to model various aspects of a software system before it exists. Creativity, past experience, a sense of what makes "good" software, and a commitment to quality are success factors for a competent design. However, the design process is not always a straightforward procedure ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microsoft Windows
Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sectors of the computing industry – Windows (unqualified) for a consumer or corporate workstation, Windows Server for a Server (computing), server and Windows IoT for an embedded system. Windows is sold as either a consumer retail product or licensed to Original equipment manufacturer, third-party hardware manufacturers who sell products Software bundles, bundled with Windows. The first version of Windows, Windows 1.0, was released on November 20, 1985, as a graphical operating system shell for MS-DOS in response to the growing interest in graphical user interfaces (GUIs). The name "Windows" is a reference to the windowing system in GUIs. The 1990 release of Windows 3.0 catapulted its market success and led to various other product families ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Class Diagram
In software engineering, a class diagram in the Unified Modeling Language (UML) is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations (or methods), and the relationships among objects. The class diagram is the main building block of object-oriented modeling. It is used for general conceptual modeling of the structure of the application, and for detailed modeling, translating the models into programming code. Class diagrams can also be used for data modeling Data modeling in software engineering is the process of creating a data model for an information system by applying certain formal techniques. It may be applied as part of broader Model-driven engineering (MDE) concept. Overview Data modeli .... The classes in a class diagram represent both the main elements, interactions in the application, and the classes to be programmed. In the diagram, classes are represented with boxes that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unified Modeling Language
The Unified Modeling Language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system. UML provides a standard notation for many types of diagrams which can be roughly divided into three main groups: behavior diagrams, interaction diagrams, and structure diagrams. The creation of UML was originally motivated by the desire to standardize the disparate notational systems and approaches to software design. It was developed at Rational Software in 1994–1995, with further development led by them through 1996. In 1997, UML was adopted as a standard by the Object Management Group (OMG) and has been managed by this organization ever since. In 2005, UML was also published by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) as the ISO/IEC 19501 standard. Since then the standard has been periodically revised to cover the latest revision of UML. In ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progress Bar
A progress bar is a graphical control element used to visualize the progression of an extended computer operation, such as a download, file transfer, or installation. Sometimes, the graphic is accompanied by a textual representation of the progress in a percent format. The concept can also be regarded to include "playback bars" in Media player (software), media players that keep track of the current location in the duration of a media file. A more recent development is the , which is used in situations where the extent of the task is unknown or the progress of the task cannot be determined in a way that could be expressed as a percentage. This bar uses motion or some other indicator (such as a barber's pole pattern) to show that progress is taking place, rather than using the size of the filled portion to show the total amount of progress, making it more like a throbber than a progress bar. There are also indeterminate progress indicators, which are not bar shaped. History Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weak Reference
In computer programming, a weak reference is a reference that does not protect the referenced object from collection by a garbage collector, unlike a strong reference. An object referenced ''only'' by weak references – meaning "every chain of references that reaches the object includes at least one weak reference as a link" – is considered '' weakly reachable,'' and can be treated as unreachable and so may be collected at any time. Some garbage-collected languages feature or support various levels of weak references, such as C#, Lua, Java, Lisp, OCaml, MATLAB, Perl, Python and PHP since the version 7.4. Uses Weak references have a number of common uses. When using reference counting garbage collection, weak references can break reference cycles, by using a weak reference for a link in the cycle. When one has an associative array (mapping, hash map) whose keys are (references to) objects, for example to hold auxiliary data about objects, using weak references for the keys a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dispose Pattern
In object-oriented programming, the dispose pattern is a design pattern for resource management. In this pattern, a resource is held by an object, and released by calling a conventional method – usually called close, dispose, free, release depending on the language – which releases any resources the object is holding onto. Many programming languages offer language constructs to avoid having to call the dispose method explicitly in common situations. The dispose pattern is primarily used in languages whose runtime environment have automatic garbage collection (see motivation below). Motivation Wrapping resources in objects Wrapping resources in objects is the object-oriented form of encapsulation, and underlies the dispose pattern. Resources are typically represented by handles (abstract references), concretely usually integers, which are used to communicate with an external system that provides the resource. For example, files are provided by the operating system (sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Garbage Collection (computer Science)
In computer science, garbage collection (GC) is a form of automatic memory management. The ''garbage collector'' attempts to reclaim memory that was allocated by the program, but is no longer referenced; such memory is called ''garbage (computer science), garbage''. Garbage collection was invented by American computer scientist John McCarthy (computer scientist), John McCarthy around 1959 to simplify manual memory management in Lisp (programming language), Lisp. Garbage collection relieves the programmer from doing manual memory management, where the programmer specifies what objects to de-allocate and return to the memory system and when to do so. Other, similar techniques include stack-based memory allocation, stack allocation, region inference, and memory ownership, and combinations thereof. Garbage collection may take a significant proportion of a program's total processing time, and affect computer performance, performance as a result. Resources other than memory, such a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lapsed Listener Problem
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. Ethan Henry and Ed Lycklama It originates in the , 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 st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Leak
In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that memory which is no longer needed is not released. A memory leak may also happen when an object is stored in memory but cannot be accessed by the running code (i.e. unreachable memory). A memory leak has symptoms similar to a number of other problems and generally can only be diagnosed by a programmer with access to the program's source code. A related concept is the "space leak", which is when a program consumes excessive memory but does eventually release it. Because they can exhaust available system memory as an application runs, memory leaks are often the cause of or a contributing factor to software aging. Effects Minor leaks If a program has a memory leak and its memory usage is steadily increasing, there will not usually be an immediate symptom. In modern operating systems, normal memory used by an application is releas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Singleton Pattern
In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems in object-oriented software. The pattern is useful when exactly one object is needed to coordinate actions across a system. More specifically, the singleton pattern allows classes to: * Ensure they only have one instance * Provide easy access to that instance * Control their instantiation (for example, hiding the constructors of a class) The term comes from the mathematical concept of a singleton. Common uses Singletons are often preferred to global variables because they do not pollute the global namespace (or their containing namespace). Additionally, they permit lazy allocation and initialization, whereas global variables in many languages will always consume resources. The singleton pattern can also be used as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
