|
Circular Dependency
In software engineering, a circular dependency is a relation between two or more modules which either directly or indirectly depend on each other to function properly. Such modules are also known as mutually recursive. Overview Circular dependencies are natural in many domain models where certain objects of the same domain depend on each other. However, in software design, circular dependencies between larger software modules are considered an anti-pattern because of their negative effects. Despite this, such circular (or cyclic) dependencies have been found to be widespread among the source files of real-world software. Mutually recursive modules are, however, somewhat common in functional programming, where inductive and recursive definitions are often encouraged. Problems Circular dependencies can cause many unwanted effects in software programs. Most problematic from a software design point of view is the ''tight coupling'' of the mutually dependent modules which reduces o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software Engineering
Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' programmer'' is sometimes used as a synonym, but may also lack connotations of engineering education or skills. Engineering techniques are used to inform the software development process which involves the definition, implementation, assessment, measurement, management, change, and improvement of the software life cycle process itself. It heavily uses software configuration management which is about systematically controlling changes to the configuration, and maintaining the integrity and traceability of the configuration and code throughout the system life cycle. Modern processes use software versioning. History Beginning in the 1960s, software engineering was seen as its own type of engineering. Additionally, the development of s ... [...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 which was allocated by the program, but is no longer referenced; such memory is called '' garbage''. Garbage collection was invented by American computer scientist John McCarthy around 1959 to simplify manual memory management in 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 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 performance as a result. Resources other than memory, such as network sockets, database handles, windows, file descriptors, and device descriptors, are not typically handled by garbage collection, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dependency Hell
Dependency hell is a colloquial term for the frustration of some software users who have installed software packages which have dependencies on specific versions of other software packages. The dependency issue arises when several packages have dependencies on the same ''shared'' packages or libraries, but they depend on different and incompatible versions of the shared packages. If the shared package or library can only be installed in a single version, the user may need to address the problem by obtaining newer or older versions of the dependent packages. This, in turn, may break other dependencies and push the problem to another set of packages. Problems Dependency hell takes several forms: ; Many dependencies : An application depends on many libraries, requiring lengthy downloads, large amounts of disk space, and being very portable (all libraries are already ported enabling the application itself to be ported easily). It can also be difficult to locate all the dependencie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acyclic Dependencies Principle
The acyclic dependencies principle (ADP) is a software design principle defined by Robert C. Martin that states that "''the dependency graph of packages or components should have no cycles''". This implies that the dependencies form a directed acyclic graph. Example In this UML package diagram, package ''A'' depends on packages ''B'' and ''C''. Package ''B'' in turn depends on package ''D'', which depends on package ''C'', which in turn depends on package ''B''. The latter three dependencies create a cycle, which must be broken in order to adhere to the acyclic dependencies principle. Types of dependencies Software dependencies can either be explicit or implicit. Examples of explicit dependencies includes: * Include statements, such as #include in C/C++, using in C# and import in Java. * Dependencies stated in the build system (e.g. dependency tags in Maven configuration). Examples of implicit dependencies includes: * Relying on specific behaviour that is not well-defined by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observer Pattern
In software design and engineering, the observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is often used for implementing distributed event-handling systems in event-driven software. In such systems, the subject is usually named a "stream of events" or "stream source of events" while the observers are called "sinks of events." The stream nomenclature alludes to a physical setup in which the observers are physically separated and have no control over the emitted events from the subject/stream source. This pattern thus suits any process by which data arrives from some input that is not available to the CPU at startup, but instead arrives seemingly at random ( HTTP requests, GPIO data, user input from peripherals, distributed databases and blockchains, etc.). Most modern programming languages ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Patterns
''Design Patterns: Elements of Reusable Object-Oriented Software'' (1994) is a software engineering book describing software design patterns. The book was written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, with a foreword by Grady Booch. The book is divided into two parts, with the first two chapters exploring the capabilities and pitfalls of object-oriented programming, and the remaining chapters describing 23 classic software design patterns. The book includes examples in C++ and Smalltalk. It has been influential to the field of software engineering and is regarded as an important source for object-oriented design theory and practice. More than 500,000 copies have been sold in English and in 13 other languages. The authors are often referred to as the Gang of Four (GoF). History The book started at a birds of a feather (BoF) session at OOPSLA '90, "Towards an Architecture Handbook", run by Bruce Anderson, where Erich Gamma and Richard Helm met a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Callback (computer Programming)
In computer programming, a callback or callback function is any reference to executable code that is passed as an argument to another piece of code; that code is expected to ''call back'' (execute) the callback function as part of its job. This execution may be immediate as in a synchronous callback, or it might happen at a later point in time as in an asynchronous callback. Programming languages support callbacks in different ways, often implementing them with subroutines, lambda expressions, blocks, or function pointers. Design There are two types of callbacks, differing in how they control data flow at runtime: ''blocking callbacks'' (also known as ''synchronous callbacks'' or just ''callbacks'') and ''deferred callbacks'' (also known as ''asynchronous callbacks''). While blocking callbacks are invoked before a function returns (as in the C example below), deferred callbacks may be invoked after a function returns. Deferred callbacks are often used in the context of I/ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Java (software Platform)
Java is a set of computer software and specifications developed by James Gosling at Sun Microsystems, which was later acquired by the Oracle Corporation, that provides a system for developing application software and deploying it in a cross-platform computing environment. Java is used in a wide variety of computing platforms from embedded devices and mobile phones to enterprise servers and supercomputers. Java applets, which are less common than standalone Java applications, were commonly run in secure, sandboxed environments to provide many features of native applications through being embedded in HTML pages. Writing in the Java programming language is the primary way to produce code that will be deployed as byte code in a Java virtual machine (JVM); byte code compilers are also available for other languages, including Ada, JavaScript, Python, and Ruby. In addition, several languages have been designed to run natively on the JVM, including Clojure, Groovy, and Scal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reference Counting
In computer science, reference counting is a programming technique of storing the number of references, pointers, or handles to a resource, such as an object, a block of memory, disk space, and others. In garbage collection algorithms, reference counts may be used to deallocate objects that are no longer needed. Advantages and disadvantages The main advantage of the reference counting over tracing garbage collection is that objects are reclaimed ''as soon as'' they can no longer be referenced, and in an incremental fashion, without long pauses for collection cycles and with clearly defined lifetime of every object. In real-time applications or systems with limited memory, this is important to maintain responsiveness. Reference counting is also among the simplest forms of memory management to implement. It also allows for effective management of non-memory resources such as operating system objects, which are often much scarcer than memory (tracing garbage collection systems ... [...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. Consequences A memory leak reduces the performance of the computer by reducing the amount of available memory. Eventually, in the worst case, too much of the available memory may become allocated and all or part of the syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mutual Recursion
In mathematics and computer science, mutual recursion is a form of recursion where two mathematical or computational objects, such as functions or datatypes, are defined in terms of each other. Mutual recursion is very common in functional programming and in some problem domains, such as recursive descent parsers, where the datatypes are naturally mutually recursive. Examples Datatypes The most important basic example of a datatype that can be defined by mutual recursion is a tree, which can be defined mutually recursively in terms of a forest (a list of trees). Symbolically: f: .html"_;"title="[1">[1_...,_t[k _t:_v_f A_forest_''f''_consists_of_a_list_of_trees,_while_a_tree_''t''_consists_of_a_pair_of_a_value_''v''_and_a_forest_''f''_(its_children)._This_definition_is_elegant_and_easy_to_work_with_abstractly_(such_as_when_proving_theorems_about_properties_of_trees),_as_it_expresses_a_tree_in_simple_terms:_a_list_of_one_type,_and_a_pair_of_two_types._Further,_it_matches_many_al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Domino Effect
A domino effect or chain reaction is the cumulative effect generated when a particular event triggers a chain of similar events. This term is best known as a mechanical effect and is used as an analogy to a falling row of dominoes. It typically refers to a linked sequence of events where the time between successive events is relatively small. It can be used literally (an observed series of actual collisions) or metaphorically (causal linkages within systems such as global finance or politics). The term ''domino effect'' is used both to imply that an event is inevitable or highly likely (as it has already started to happen), and conversely to imply that an event is impossible or highly unlikely (the one domino left standing). Demonstration of the effect The domino effect can easily be visualized by placing a row of dominoes upright, each separated by a small distance. Upon pushing the first domino, the next domino in line will be knocked over, and so on, thus firing a linear ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
