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Virtual Function
In object-oriented programming, in languages such as C++, and Object Pascal, a virtual function or virtual method is an inheritable and overridable function or method for which dynamic dispatch is facilitated. This concept is an important part of the (runtime) polymorphism portion of object-oriented programming (OOP). In short, a virtual function defines a target function to be executed, but the target might not be known at compile time. Most programming languages, such as JavaScript, PHP and Python, treat all methods as virtual by default and do not provide a modifier to change this behavior. However, some languages provide modifiers to prevent methods from being overridden by derived classes (such as the ''final'' keyword in Java and PHP). Purpose The concept of the virtual function solves the following problem: In object-oriented programming, when a derived class inherits from a base class, an object of the derived class may be referred to via a pointer or r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object-oriented Programming
Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of procedures (often known as '' methods''). A common feature of objects is that procedures (or methods) are attached to them and can access and modify the object's data fields. In this brand of OOP, there is usually a special name such as or used to refer to the current object. In OOP, computer programs are designed by making them out of objects that interact with one another. OOP languages are diverse, but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types. Many of the most widely used programming languages (such as C++, Java, Python, etc.) are multi-paradigm and they support object-oriented programming to a greater or lesser degree, typically in combination with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Method Implementation
In object-oriented programming, a class implementation file is often used to contain the implementation code for the method(s) of a class. Programming languages like C and C++ make use of these implementation files so as to separate the interface and implementation of these methods. Motivation Using this structure, a class definition file containing the declaration of the class and its members is also created. If the class definition has been included and the implementation file for its methods is available, the user can instantiate an object of the class. The purpose of this structure is to keep the implementation code hidden, but allow the user to view the design. Users make use of the public interface of an object so as to make creating objects as simple as possible, ensuring that client code does not distract the user with unnecessary details of the class's implementation. This allows the user the information needed to use the class effectively, but prevents him or her ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Static Dispatch
In computing, static dispatch is a form of polymorphism fully resolved during compile time. It is a form of ''method dispatch,'' which describes how a language or environment will select which implementation of a method or function to use. Examples are templates in C++, and generic programming in other languages, in conjunction with function overloading (including operator overloading). Code is said to be monomorphised, with specific data types deduced and traced through the call graph, in order to instantiate specific versions of generic functions, and select specific function calls based on the supplied definitions. This contrasts with dynamic dispatch, which is based on runtime information (such as vtable pointers and other forms of run time type information). Static dispatch is possible because there is a guarantee of there only ever being a single implementation of the method in question. Static dispatch is typically faster than dynamic dispatch which by nature ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abstract Factory Pattern
The abstract factory pattern provides a way to encapsulate a group of individual factories that have a common theme without specifying their concrete classes. In normal usage, the client software creates a concrete implementation of the abstract factory and then uses the generic interface of the factory to create the concrete objects that are part of the theme. The client does not know (or care) which concrete objects it gets from each of these internal factories, since it uses only the generic interfaces of their products. This pattern separates the details of implementation of a set of objects from their general usage and relies on object composition, as object creation is implemented in methods exposed in the factory interface. An example of this would be an abstract factory class DocumentCreator that provides interfaces to create a number of products (e.g., createLetter() and createResume()). The system would have any number of derived concrete versions of the DocumentCreator c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Pattern (computer Science)
In software engineering, a software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into source or machine code. Rather, it is a description or template for how to solve a problem that can be used in many different situations. Design patterns are formalized best practices that the programmer can use to solve common problems when designing an application or system. Object-oriented design patterns typically show relationships and interactions between classes or objects, without specifying the final application classes or objects that are involved. Patterns that imply mutable state may be unsuited for functional programming languages. Some patterns can be rendered unnecessary in languages that have built-in support for solving the problem they are trying to solve, and object-oriented patterns are not necessarily suitable for non-object-oriented lan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Runtime (program Lifecycle Phase)
In computer science, runtime, run time, or execution time is the final phase of a computer programs life cycle, in which the code is being executed on the computer's central processing unit (CPU) as machine code. In other words, "runtime" is the running phase of a program. A runtime error is detected after or during the execution (running state) of a program, whereas a compile-time error is detected by the compiler before the program is ever executed. Type checking, register allocation, code generation, and code optimization are typically done at compile time, but may be done at runtime depending on the particular language and compiler. Many other runtime errors exist and are handled differently by different programming languages, such as division by zero errors, domain errors, array subscript out of bounds errors, arithmetic underflow errors, several types of underflow and overflow errors, and many other runtime errors generally considered as software bugs which may or may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Runtime System
In computer programming, a runtime system or runtime environment is a sub-system that exists both in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile time and runtime division from compiled languages, which similarly distinguishes the computer processes involved in the creation of a program (compilation) and its execution in the target machine (the run time). Most programming languages have some form of runtime system that provides an environment in which programs run. This environment may address a number of issues including the management of application memory, how the program accesses variables, mechanisms for passing parameters between procedures, interfacing with the operating system, and otherwise. The compiler makes assumptions depending on the specific runtime system to generate correct code. Typically the runtime system will have some responsibility for setting up and managing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Link Time
In computer science, link time refers to the period of time, during the creation of a computer program, in which a linker is being applied to that program. Link time occurs after compile time and before runtime (when a program is executed). It is common to speak of ''link time operations'' (the operations performed by a linker) or ''link time requirements'' (programming language requirements that must be met by compiled source code for it to be successfully linked). Link time operations The operations performed at link time usually include fixing up the addresses of externally referenced objects and functions, various kinds of cross module checks (e.g. type checks on externally visible identifiers and in some languages instantiation of templates). Some optimizing compilers delay code generation until link time because it is here that information about a complete program is available to them. Resolving external variables in a program is also done at link time. The link-time ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Compile Time
In computer science, compile time (or compile-time) describes the time window during which a computer program is compiled. The term is used as an adjective to describe concepts related to the context of program compilation, as opposed to concepts related to the context of program execution ( runtime). For example, ''compile-time requirements'' are programming language requirements that must be met by source code before compilation and ''compile-time properties'' are properties of the program that can be reasoned about during compilation. The actual length of time it takes to compile a program is usually referred to as ''compilation time''. Compile time/Early binding vs Run time The determination of execution model have been set during the compile time stage. Run time- the method of execution and allocation - have been set during the run time and are based on the run time dynamicity. Overview Most compilers have at least the following compiler phases (which therefore occur at c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Undefined Behavior
In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. This is different from unspecified behavior, for which the language specification does not prescribe a result, and implementation-defined behavior that defers to the documentation of another component of the platform (such as the ABI or the translator documentation). In the C community, undefined behavior may be humorously referred to as "nasal demons", after a comp.std.c post that explained undefined behavior as allowing the compiler to do anything it chooses, even "to make demons fly out of your nose". Overview Some programming languages allow a program to operate differently or even have a different control flow than the source code, as long as it exhibits the same user-visible side effects, ''if undefined behavior never happens during program execution''. Undefined beha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Destructor (computer Science)
In object-oriented programming, a destructor (sometimes abbreviated dtor) is a method which is invoked mechanically just before the memory of the object is released. It can happen when its lifetime is bound to scope and the execution leaves the scope, when it is embedded in another object whose lifetime ends, or when it was allocated dynamically and is released explicitly. Its main purpose is to free the resources (memory allocations, open files or sockets, database connections, resource locks, etc.) which were acquired by the object during its life and/or deregister from other entities which may keep references to it. Use of destructors is needed for the process of Resource Acquisition Is Initialization (RAII). With most kinds of automatic garbage collection algorithms, the releasing of memory may happen a long time after the object becomes unreachable, making destructors (called finalizers in this case) unsuitable for most purposes. In such languages, the freeing of resource ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Constructor (computer Science)
In class-based, object-oriented programming, a constructor (abbreviation: ctor) is a special type of subroutine called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables. A constructor resembles an instance method, but it differs from a method in that it has no explicit return type, it is not implicitly inherited and it usually has different rules for scope modifiers. Constructors often have the same name as the declaring class. They have the task of initializing the object's data members and of establishing the invariant of the class, failing if the invariant is invalid. A properly written constructor leaves the resulting object in a ''valid'' state. Immutable objects must be initialized in a constructor. Most languages allow overloading the constructor in that there can be more than one constructor for a class, with differing parameters. Some languages take consideration of som ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
