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Decorator Pattern
In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object, dynamically, without affecting the behavior of other objects from the same class. The decorator pattern is often useful for adhering to the Single Responsibility Principle, as it allows functionality to be divided between classes with unique areas of concern as well as to the Open-Closed Principle, by allowing the functionality of a class to be extended without being modified. Decorator use can be more efficient than subclassing, because an object's behavior can be augmented without defining an entirely new object. Overview The ''decorator'' design pattern is one of the twenty-three well-known ''design patterns''; these describe how to solve recurring design problems and design flexible and reusable object-oriented software—that is, objects which are easier to implement, change, test, and reuse. What problems can it solve? * Responsibilities sh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Facade Pattern
The facade pattern (also spelled ''façade'') is a software-design pattern commonly used in object-oriented programming. Analogous to a facade in architecture, a facade is an object that serves as a front-facing interface masking more complex underlying or structural code. A facade can: * improve the readability and usability of a software library by masking interaction with more complex components behind a single (and often simplified) API * provide a context-specific interface to more generic functionality (complete with context-specific input validation) *serve as a launching point for a broader refactor of monolithic or tightly-coupled systems in favor of more loosely-coupled code Developers often use the facade design pattern when a system is very complex or difficult to understand because the system has many interdependent classes or because its source code is unavailable. This pattern hides the complexities of the larger system and provides a simpler interface to the cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Python Syntax And Semantics
The syntax of the Python programming language is the set of rules that defines how a Python program will be written and interpreted (by both the runtime system and by human readers). The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages. Design philosophy Python was designed to be a highly readable language. It has a relatively uncluttered visual layout and uses English keywords frequently where other languages use punctuation. Python aims to be simple and consistent in the design of its syntax, encapsulated in the mantra , from the Zen of Python. This mantra is deliberately opposed to the Perl and Ruby mantra, "there's more than one way to do it". Keywords Python has 35 keywords or ''reserved words''; they cannot be used as identifiers. *and *as *assert *async *await *break *class *continue *def *del *elif *else *except *False *finally *for *from *global *if *import *in *is *lambda *None * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Java Platform, Standard Edition
Java Platform, Standard Edition (Java SE) is a computing platform for development and deployment of portable code for desktop and server environments. Java SE was formerly known as Java 2 Platform, Standard Edition (J2SE). The platform uses Java programming language and is part of the Java software-platform family. Java SE defines a range of general-purpose APIs—such as Java APIs for the Java Class Library—and also includes the Java Language Specification and the Java Virtual Machine Specification. OpenJDK is the official reference implementation since version 7. Nomenclature, standards and specifications The platform was known as ''Java 2 Platform, Standard Edition'' or ''J2SE'' from version 1.2, until the name was changed to ''Java Platform, Standard Edition'' or ''Java SE'' in version 1.5. The "SE" is used to distinguish the base platform from the Enterprise Edition (Java EE) and Micro Edition (Java ME) platforms. The "2" was originally intended to emphasize the maj ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polymorphism (computer Science)
In programming language theory and type theory, polymorphism is the provision of a single interface to entities of different types or the use of a single symbol to represent multiple different types.: "Polymorphic types are types whose operations are applicable to values of more than one type." The concept is borrowed from a principle in biology where an organism or species can have many different forms or stages. The most commonly recognized major classes of polymorphism are: * ''Ad hoc polymorphism'': defines a common interface for an arbitrary set of individually specified types. * ''Parametric polymorphism'': not specifying concrete types and instead use abstract symbols that can substitute for any type. * ''Subtyping'' (also called ''subtype polymorphism'' or ''inclusion polymorphism''): when a name denotes instances of many different classes related by some common superclass. History Interest in polymorphic type systems developed significantly in the 1960s, with practica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adapter Pattern
In software engineering, the adapter pattern is a software design pattern (also known as wrapper, an alternative naming shared with the decorator pattern) that allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code. An example is an adapter that converts the interface of a Document Object Model of an XML document into a tree structure that can be displayed. Overview The adapter design pattern is one of the twenty-three well-known Gang of Four design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse. The adapter design pattern solves problems like: * How can a class be reused that does not have an interface that a client requires? * How can classes that have incompatible interfaces work together? * How can an alternative interfa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visitor Pattern
In object-oriented programming and software engineering, the visitor design pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying the structures. It is one way to follow the open/closed principle. In essence, the visitor allows adding new virtual functions to a family of classes, without modifying the classes. Instead, a visitor class is created that implements all of the appropriate specializations of the virtual function. The visitor takes the instance reference as input, and implements the goal through double dispatch. Overview The Visitor design pattern is one of the twenty-three well-known '' Gang of Four design patterns'' that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse. What ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adapter Pattern
In software engineering, the adapter pattern is a software design pattern (also known as wrapper, an alternative naming shared with the decorator pattern) that allows the interface of an existing class to be used as another interface. It is often used to make existing classes work with others without modifying their source code. An example is an adapter that converts the interface of a Document Object Model of an XML document into a tree structure that can be displayed. Overview The adapter design pattern is one of the twenty-three well-known Gang of Four design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse. The adapter design pattern solves problems like: * How can a class be reused that does not have an interface that a client requires? * How can classes that have incompatible interfaces work together? * How can an alternative interfa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flyweight Pattern
In computer programming, the flyweight software design pattern refers to an object that minimizes memory usage by sharing some of its data with other similar objects. The flyweight pattern is one of twenty-three well-known '' GoF design patterns''. These patterns promote flexible object-oriented software design, which is easier to implement, change, test, and reuse. In other contexts, the idea of sharing data structures is called hash consing. The term was first coined, and the idea extensively explored, by Paul Calder and Mark Linton in 1990 to efficiently handle glyph information in a WYSIWYG document editor. Similar techniques were already used in other systems, however, as early as 1988. Overview The flyweight pattern is useful when dealing with large numbers of objects with simple repeated elements that would use a large amount of memory if individually stored. It is common to hold shared data in external data structures and pass it to the objects temporarily when the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
State Pattern
The state pattern is a behavioral software design pattern that allows an object to alter its behavior when its internal state changes. This pattern is close to the concept of finite-state machines. The state pattern can be interpreted as a strategy pattern, which is able to switch a strategy through invocations of methods defined in the pattern's interface. The state pattern is used in computer programming to encapsulate varying behavior for the same object, based on its internal state. This can be a cleaner way for an object to change its behavior at runtime without resorting to conditional statements and thus improve maintainability. Overview The state design pattern is one of twenty-three design patterns documented by the Gang of Four that describe how to solve recurring design problems. Such problems cover the design of flexible and reusable object-oriented software, such as objects that are easy to implement, change, test, and reuse. The state pattern is set to solve two ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Command Pattern
In object-oriented programming, the command pattern is a behavioral design pattern in which an object is used to encapsulate all information needed to perform an action or trigger an event at a later time. This information includes the method name, the object that owns the method and values for the method parameters. Four terms always associated with the command pattern are ''command'', ''receiver'', ''invoker'' and ''client''. A ''command'' object knows about ''receiver'' and invokes a method of the receiver. Values for parameters of the receiver method are stored in the command. The receiver object to execute these methods is also stored in the command object by aggregation. The ''receiver'' then does the work when the execute() method in ''command'' is called. An ''invoker'' object knows how to execute a command, and optionally does bookkeeping about the command execution. The invoker does not know anything about a concrete command, it knows only about the command ''interface' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scrollbar
A scrollbar is an interaction technique or widget in which continuous text, pictures, or any other content can be scrolled in a predetermined direction (up, down, left, or right) on a computer display, window, or viewport so that all of the content can be viewed, even if only a fraction of the content can be seen on a device's screen at one time. It offers a solution to the problem of navigation to a known or unknown location within a two-dimensional information space. It was also known as a handle in the very first GUIs. They are present in a wide range of electronic devices including computers, graphing calculators, mobile phones, and portable media players. The user interacts with the scrollbar elements using some method of direct action, the scrollbar translates that action into scrolling commands, and the user receives feedback through a visual updating of both the scrollbar elements and the scrolled content. Although scrollbar designs differ throughout their history, they ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scrolling
In computer displays, filmmaking, television production, and other kinetic displays, scrolling is sliding text, images or video across a monitor or display, vertically or horizontally. "Scrolling," as such, does not change the layout of the text or pictures but moves ( pans or tilts) the user's view across what is apparently a larger image that is not wholly seen. A common television and movie special effect is to scroll credits, while leaving the background stationary. Scrolling may take place completely without user intervention (as in film credits) or, on an interactive device, be triggered by touchscreen or a keypress and continue without further intervention until a further user action, or be entirely controlled by input devices. Scrolling may take place in discrete increments (perhaps one or a few lines of text at a time), or continuously (smooth scrolling). Frame rate is the speed at which an entire image is redisplayed. It is related to scrolling in that changes to text a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
