In object-oriented programming, a class is a programming language construct that is used as a blueprint to create objects. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs A programming language is an Artificial language that can be used to write programs which control the behavior of a machine particularly a Computer. In its simplest embodiment an object is an allocated region of storage This blueprint includes attributes and methods that the created objects all share. In Computing, an attribute is a specification that defines a property of an object element or file In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods
More technically, a class is a cohesive package that consists of a particular kind of metadata. In Computer programming, cohesion is a measure of how strongly-related and focused the various responsibilities of a software module are Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media It describes the rules by which objects behave; these objects are referred to as instances of that class. In its simplest embodiment an object is an allocated region of storage A class has both an interface and a structure. The interface describes how the class and its instances can be interacted with via methods, while the structure describes how the data is partitioned into attributes within an instance. In Computer science, data is anything in a form suitable for use with a Computer. A class is the most specific type of an object in relation to a specific layer. A data type in Programming languages is an attribute of a datum which tells the computer (and the programmer something about the kind of datum it is In Object-oriented design, a layer is a group of classes that have the same set of link-time module dependencies to other modules A class may also have a representation (metaobject) at runtime, which provides runtime support for manipulating the class-related metadata. In Computer science, a metaobject or meta-object is any entity that manipulates creates describes or implements other objects The object that the
Programming languages that support classes all subtly differ in their support for various class-related features. Most support various forms of class inheritance. In Object-oriented programming, inheritance is a way to form new classes (instances of which are called objects using classes that have already been defined Many languages also support features providing encapsulation, such as access specifiers. In Computer science, the principle of information hiding is the hiding of design decisions in a computer program that are most likely to change thus protecting
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Reasons for using classes
Classes, when used properly, can accelerate development by reducing redundant code entry, testing and bug fixing. A software bug (or just “bug” is an error flaw mistake Failure, fault or “undocumented feature” in a Computer program that prevents it If a class has been thoroughly tested and is known to be a solid work, it stands to reason that using that well-tested class or extending it will reduce, if not eliminate, the possibility of bugs propagating into the code. In the case of extension, new code is being added, so it also requires the same level of testing before it can be considered solid.
Another reason for using classes is to simplify the relationships of interrelated data. Rather than writing code to repeatedly call a GUI window drawing subroutine on the terminal screen (as would be typical for structured programming), it is more intuitive to represent the window as an object and tell it to draw itself as necessary. In Computing, a window is a visual area usually rectangular in shape containing some kind of User interface, displaying the output of and allowing input for one Structured programming can be seen as a subset or subdiscipline of Procedural programming, one of the major Programming paradigms It is most famous for removing or With classes, GUI items that are similar to windows (such as dialog boxes) can simply inherit most of their functionality and data structures from the window class. In Computer programming a window class is a structure fundamental to the Microsoft Windows ( Win16 and Win32) Operating systems and The programmer then need only add code to the dialog class that is unique to its operation. Indeed, GUIs are a very common and useful application of classes, and GUI programming is generally much easier with a good class framework.
Instantiation
A class is used to create new instances (objects) by instantiating the class. In its simplest embodiment an object is an allocated region of storage
Instances of a class share the same set of attributes, yet may differ in what those attributes contain. For example, a class "Person" would describe the attributes common to all instances of the Person class. Each person is generally alike, but varies in such attributes as "height" and "weight". The class would list types of such attributes and also define the actions which a person can perform: "run", "jump", "sleep", "walk", etc. One of the benefits of programming with classes is that all instances of a particular class will follow the defined behavior of the class they instantiate.
In most languages, the structures as defined by the class determine how the memory used by its instances will be laid out. This technique is known as the cookie-cutter model. The alternative to the cookie-cutter model is that of for example Python, where objects are structured as associative key-value containers. Python is a general-purpose High-level programming language. Its design philosophy emphasizes programmer productivity and code readability In such models, objects that are instances of the same class could contain different instance variables, as state can be dynamically added to the object. This may resemble prototype-based languages in some ways, but it is not equivalent. Prototype-based programming is a style of Object-oriented programming in which classes are not present and behavior reuse (known as inheritance in class-based
Interfaces and methods
Note: the term "interface" here isn't referring to a Java interface, although the two are closely related. Interface generally refers to an abstraction that an entity provides of itself to the outside In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods An interface in the Java programming language is an Abstract type that is used to specify an interface (in the generic sense of the term that classes
Objects define their interaction with the outside world through the methods that they expose. A method, or instance method, is a subroutine (function) with a special property that it has access to data stored in an object (instance). In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger Methods that manipulate the data of the object and perform tasks are sometimes described as behavior. Behavior or behaviour (see spelling differences) refers to the actions or Reactions of an object or Organism, usually
Methods form the object's interface with the outside world; the buttons on the front of your television set, for example, are the interface between you and the electrical wiring on the other side of its plastic casing. You press the "power" button to toggle the television on and off. In this example, the television is the instance, each method is represented by a button, and all the buttons together comprise the interface. In its most common form, an interface is a specification of a group of related methods without any associated implementation of the methods.
Every class implements (or realizes) an interface by providing structure (i. e. data and state) and method implementations (i. e. providing code that specifies how methods work). There is a distinction between the definition of an interface and the implementation of that interface. In most languages, this line is usually blurred, because a class declaration both defines and implements an interface. Some languages, however, provide features that help separate interface and implementation. For example, an abstract class can define an interface without providing implementation, and in the Dylan language, class definitions do not even define interfaces. The Dylan Programming language is a multi-paradigm language that includes support for functional
Interfaces may also be defined to include a set of auxiliary functions called static methods or class methods. Static methods, like instance methods, are exclusively associated with the class. They differ with instance methods in that they do not work with instances of the class; that is, static methods neither require an instance of the class nor can access the data of such an instance. For example, getting the total number of televisions in existence could be a static method of the television class. This method is clearly associated with the class, yet is outside the domain of each individual instance of the class. Another example is a static method that finds a particular instance out of the set of all television sets.
Languages that support class inheritance also allow classes to inherit interfaces from the classes that they are derived from. In languages that support access specifiers, the interface of a class is considered to be the set of public members of the class, including both methods and attributes (via implicit getter and setter methods); any private members or internal data structures are not intended to be depended on by client code and thus are not part of the interface. In Computer science, a mutator method is a method used to control changes to a variable
The object-oriented programming methodology is designed in such a way that the operations of any interface of a class are usually chosen to be independent of each other. It results in a client-server (or layered) design where servers do not depend in any way on the clients. The client-server Software architecture model distinguishes client systems from server systems which communicate over a Computer network An interface places no requirements for clients to invoke the operations of one interface in any particular order. This approach has the benefit that client code can assume that the operations of an interface are available for use whenever the client holds a valid reference to the object.
Structure of a class
Along with having an interface, a class contains a description of structure of data stored in the instances of the class. Unified Modeling Language ( UML) is a standardized general-purpose Modeling language in the field of Software engineering. In Computer science, data is anything in a form suitable for use with a Computer. The data is partitioned into attributes (or properties, fields, data members). Going back to the television set example, the myriad attributes, such as size and whether it supports color, together comprise its structure. A class represents the full description of a television, including its attributes (structure) and buttons (interface).
The state of an instance's data is stored in some resource, such as memory or a file. In Computer science and Automata theory, a state is a unique configuration of information in a program or machine The storage is assumed to be located in a specific location, such that it is possible to access the instance through references to the identity of the instances. In Computer science, a reference is an object containing information which refers to data stored elsewhere as opposed to containing the data itself An identity in Object-oriented programming, Object-oriented design and Object-oriented analysis describes the property of objects that distinguishes However, the actual storage location associated with an instance may change with time. In such situations, the identity of the object does not change. The state is encapsulated and every access to the state occurs through methods of the class.
A class also describes a set of invariants that are preserved by every method in the class. This article is about class invariants in Computer programming, for use of the term in Mathematics, see Equivalence class and Invariant An invariant is a constraint on the state of an object that should be satisfied by every object of the class. The main purpose of the invariants is to establish what objects belong to the class. An invariant is what distinguishes data types and classes from each other; that is, a class does not allow use of all possible values for the state of the object, and instead allows only those values that are well-defined by the semantics of the intended use of the data type. A data type in Programming languages is an attribute of a datum which tells the computer (and the programmer something about the kind of datum it is The set of supported (public) methods often implicitly establishes an invariant. Some programming languages support specification of invariants as part of the definition of the class, and enforce them through the type system. Encapsulation of state is necessary for being able to enforce the invariants of the class.
Some languages allow an implementation of a class to specify constructor and destructor methods that allow creation and destruction of objects of the class. In Object-oriented programming, a constructor (sometimes shortened to ctor) in a class is a special block of statements called when an object is created In Object-oriented programming, a destructor (sometimes shortened to dtor) is a method which is automatically invoked when the object is destroyed A constructor that takes arguments can be used to create an object from data. The main purpose of a constructor is to establish the invariant of the class, failing if the invariant isn't valid. The main purpose of a destructor is to destroy the identity of the object, invalidating any references in the process. In some languages, a destructor can return a value which can then be used to obtain a public representation (transfer encoding) of an object of a class and simultaneously destroy the copy of the object stored in current thread's memory. Constructors and destructors are also sometimes used to reserve and release, respectively, resources associated with the object. Constructors and destructors are sometimes specified as static methods.
A class may also contain static attributes or class attributes, which contain data that are specific to the class yet are common to all instances of the class. If the class itself is treated as an instance of a hypothetical metaclass, static attributes and static methods would be instance attributes and instance methods of that metaclass. In object-oriented programming, a metaclass is a class whose instances are classes
Run-time representation of classes
As a data type, a class is usually considered as a compile-time construct. A language may also support prototype or factory metaobjects that represent run-time information about classes, or even represent metadata that provides access to reflection facilities and ability to manipulate data structure formats at run-time. A prototype is an original type form or instance of something serving as a typical example basis or standard for other things of the same category The factory method pattern is an Object-oriented design pattern. In Computer science, a metaobject or meta-object is any entity that manipulates creates describes or implements other objects The object that the In Computer science, reflection is the process by which a Computer program can observe and modify its own structure and behavior Many languages distinguish this kind of run-time type information about classes from a class on the basis that the information is not needed at run-time. In programming RTTI ( Run-Time Type Information, or Run-Time Type Identification) refers to a C++ system that keeps information about an object's Some dynamic languages do not make strict distinctions between run-time and compile-time constructs, and therefore may not distinguish between metaobjects and classes.
For example: if Human is a metaobject representing the class Person, then instances of class Person can be created by using the facilities of the Human metaobject. In Computer science, a metaobject or meta-object is any entity that manipulates creates describes or implements other objects The object that the In Computer science, a metaobject or meta-object is any entity that manipulates creates describes or implements other objects The object that the
Information hiding and encapsulation
Many languages support the concept of information hiding and encapsulation, typically with access specifiers for class members. In Computer science, the principle of information hiding is the hiding of design decisions in a computer program that are most likely to change thus protecting Access specifiers specify constraints on who can access which class members. Some access specifiers may also control how classes inherit such constraints. Their primary purpose is to separate the interface of a class with its implementation.
A common set of access specifiers that many object-oriented languages support is:
- Private restricts the access to the class itself. Only methods that are part of the same class can access private members.
- Protected allows the class itself and all its subclasses to access the member.
- Public means that all clients can access the member by its name.
Note that although many languages support these access specifiers, the semantics of them may subtly differ in each.
A common usage of access specifiers is to separate the internal data structures of a class from its interface; that is, the internal data structures are private. Public accessor methods can be used to inspect or alter such private data. In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods The various object-oriented programming languages enforce this to various degrees. For example, the Java language does not allow client code to access the private data of a class at all, whereas in languages like Objective-C or Perl client code can do whatever it wants. Objective-C is a reflective, object-oriented Programming language which adds Smalltalk -style messaging to C. NOTES FOR EDITORS "Perl" is not an acronym (read the "Name" section below In C++ language, private methods are visible but not accessible in the interface; however, they are commonly made invisible by explicitly declaring fully abstract classes that represent the interfaces of the class. C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language.
Access specifiers do not necessarily control visibility, in that even private members may be visible to client code. In some languages, an inaccessible but visible member may be referred to at run-time (e. g. pointer to it can be returned from member functions), but all attempts to use it by referring to the name of the member from client code will be prevented by the type checker. Object-oriented design uses the access specifiers in conjunction with careful design of public method implementations to enforce class invariants. Access specifiers are intended to protect against accidental use of members by clients, but are not suitable for run-time protection of object's data.
In addition, some languages, such as C++, support a mechanism where a function explicitly declared as friend of the class may access the members designated as private or protected.
Associations between classes
In object-oriented design and in UML, an association between two classes is a type of a link between the corresponding objects. In Object-oriented programming, Association defines a relationship between classes of objects which allows one object instance to cause another to perform an action on its behalf Object-oriented design is part of OO methodology and it forces programmers to think in terms of objects, rather than procedures when they plan their code Unified Modeling Language ( UML) is a standardized general-purpose Modeling language in the field of Software engineering. A (two-way) association between classes A and B describes a relationship between each object of class A and some objects of class B, and vice versa. Associations are often named with a verb, such as "subscribes-to".
An association role type describes the role type of an instance of a class when the instance participates in an association. An association role type is related to each end of the association. A role describes an instance of a class from the point of view of a situation in which the instance participates in the association. Role types are collections of role (instance)s grouped by their similar properties. For example, a "subscriber" role type describes the property common to instances of the class "Person" when they participate in a "subscribes-to" relationship with the class "Magazine". Also, a "Magazine" has the "subscribed magazine" role type when the subscribers subscribe-to it.
Association role multiplicity describes how many instances correspond to each instance of the other class(es) of the association. Common multiplicities are "0. . 1", "1. . 1", "1. . *" and "0. . *", where the "*" specifies any number of instances.
There are some special kinds of associations between classes.
Composition
Composition between class A and class B describes a "part-of" relationship where instances of class B have shorter lifetime than the lifetime of the corresponding instances of the enclosing class. In Computer science, object composition (not to be confused with function composition) is a way and practice to combine simple objects or In Computer science, the object lifetime (or life cycle) of an object in Object-oriented programming is the time between an object's creation Class B is said to be a part of class A. This is often implemented in programming languages by allocating the data storage of instances of class A to contain a representation of instances of class B.
Aggregation is a variation of composition that describes that instances of a class are part of instances of the other class, but the constraint on lifetime of the instances is not required. The implementation of aggregation is often via a pointer or reference to the contained instance. In both cases, method implementations of the enclosing class can invoke methods of the part class. A common example of aggregation is a list class. When a list's lifetime is over, it does not necessarily mean the lifetimes of the objects within the list are also over.
Inheritance
Another type of class association is inheritance, which involves subclasses and superclasses, also known respectively as child classes (or derived classes) and parent classes (or base classes). In Object-oriented programming, inheritance is a way to form new classes (instances of which are called objects using classes that have already been defined In Computer science, a superclass is a class from which other classes are derived In Object-oriented programming, a subclass is a class that inherits some properties from its superclass. If [car] was a class, then [station wagon] and [mini-van] might be two subclasses. If [Button] is a subclass of [Control], then all buttons are controls. Subclasses usually consist of several kinds of modifications (customizations) to their respective superclasses: addition of new instance variables, addition of new methods and overriding of existing methods to support the new instance variables. Method overriding, in Object oriented programming, is a language feature that allows a subclass to provide a specific implementation of a method that is
Conceptually, a superclass should be considered as a common part of its subclasses. This factoring of commonality is one mechanism for providing reuse. Reuse is using an item more than once This includes conventional reuse where the item is used again for the same function and new-life reuse where it is used for a new function Thus, extending a superclass by modifying the existing class is also likely to narrow its applicability in various situations. In object-oriented design, careful balance between applicability and functionality of superclasses should be considered. Subclassing is different from subtyping in that subtyping deals with common behaviour whereas subclassing is concerned with common structure. In Computer science, a subtype is a Datatype that is generally related to another datatype (the supertype) by some notion of Substitutability
Some programming languages (for example C++) allow multiple inheritance - they allow a child class to have more than one parent class. C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language. Multiple inheritance refers to a feature of some object-oriented Programming languages in which a class can inherit behaviors and features from This technique has been criticized by some for its unnecessary complexity and being difficult to implement efficiently, though some projects have certainly benefited from its use. Java, for example has no multiple inheritance, as its designers felt that it would add unnecessary complexity. Java instead allows inheriting from multiple pure abstract classes (called interfaces in Java).
Sub- and superclasses are considered to exist within a hierarchy defined by the inheritance relationship. In Computer science 's Object-oriented programming, the mapped relationships of sub- and superclasses is known as a Hierarchy. If multiple inheritance is allowed, this hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a tree. In Computer science and Mathematics, a directed acyclic graph, also called a DAG, is a with no; that is for any vertex v, there In Graph theory, a tree is a graph in which any two vertices are connected by exactly one path. The hierarchy has classes as nodes and inheritance relationships as links. The levels of this hierarchy are called layers or levels of abstraction. In Object-oriented design, a layer is a group of classes that have the same set of link-time module dependencies to other modules level of abstraction' redirects here For the concept in computer science see Abstraction layer. Classes in the same level are more likely to be associated than classes in different levels. In Object-oriented programming, Association defines a relationship between classes of objects which allows one object instance to cause another to perform an action on its behalf
There are two slightly different points of view as to whether subclasses of the same class are required to be disjoint. Sometimes, subclasses of a particular class are considered to be completely disjoint. That is, every instance of a class has exactly one most-derived class, which is a subclass of every class that the instance has. This view does not allow dynamic change of object's class, as objects are assumed to be created with a fixed most-derived class. The basis for not allowing changes to object's class is that the class is a compile-time type, which does not usually change at runtime, and polymorphism is utilized for any dynamic change to the object's behavior, so this ability is not necessary. In simple terms polymorphism is the ability of one type A to appear as and be used like another type B And design that does not need to perform changes to object's type will be more robust and easy-to-use from the point of view of the users of the class.
From another point of view, subclasses are not required to be disjoint. Then there is no concept of a most-derived class, and all types in the inheritance hierarchy that are types of the instance are considered to be equally types of the instance. This view is based on a dynamic classification of objects, such that an object may change its class at runtime. Then object's class is considered to be its current structure, but changes to it are allowed. The basis for allowing changes to object's class is a perceived inconvenience caused by replacing an instance with another instance of a different type, since this would require change of all references to the original instance to be changed to refer to the new instance. When changing the object's class, references to the existing instances do not need to be replaced with references to new instances when the class of the object changes. However, this ability is not readily available in all programming languages. This analysis depends on the proposition that dynamic changes to object structure are common. This may or may not be the case in practice.
Languages without inheritance
Although class-based languages are commonly assumed to support inheritance, inheritance is not an intrinsic aspect of the concept of classes. There are languages that support classes yet do not support inheritance. Examples are earlier versions of Visual Basic. Visual Basic ( VB) is the third-generation event-driven programming language and associated development environment (IDE from These languages, sometimes called "object-based languages", do not provide the structural benefits of statically type-checked interfaces for objects. This is because in object-based languages, it is possible to use and extend data structures and attach methods to them at run-time. This precludes the compiler or interpreter from being able to check the type information specified in the source code as the type is built dynamically and not defined statically. Most of these languages allow for instance behaviour and complex operational polymorphism (see dynamic dispatch and polymorphism). In Computer science, dynamic dispatch is the process of mapping a message to a specific sequence of code ( method) at Runtime. In Computer science, polymorphism is a Programming language feature that allows values of different Data types to be handled using a
Categories of classes
There are many categories of classes depending on modifiers. Note that these categories do not necessarily categorize classes into distinct partitions. For example, while it is impossible to have a class that is both abstract and concrete, a sealed class is implicitly a concrete class, and it may be possible to have an abstract partial class.
Concrete classes
A concrete class is a class that can be instantiated. In its simplest embodiment an object is an allocated region of storage This contrasts with abstract classes as described below.
Abstract classes
An abstract class, or abstract base class (ABC), is a class that cannot be instantiated. This article discusses types with no direct members see also Abstract data type. Such a class is only meaningful if the language supports inheritance. An abstract class is designed only as a parent class from which child classes may be derived. Abstract classes are often used to represent abstract concepts or entities. In Computer science, abstraction is a mechanism and practice to reduce and factor out details so that one can focus on a few concepts at a time The incomplete features of the abstract class are then shared by a group of subclasses which add different variations of the missing pieces.
Abstract classes are superclasses which contain abstract methods and are defined such that concrete subclasses are to extend them by implementing the methods. In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods The behaviors defined by such a class are "generic" and much of the class will be undefined and unimplemented. Before a class derived from an abstract class can become concrete, i. e. a class that can be instantiated, it must implement particular methods for all the abstract methods of its parent classes.
When specifying an abstract class, the programmer is referring to a class which has elements that are meant to be implemented by inheritance. The abstraction of the class methods to be implemented by the subclasses is meant to simplify software development. Software development is the translation of a user need or marketing goal into a Software product This also enables the programmer to focus on planning and design.
Most object oriented programming languages allow the programmer to specify which classes are considered abstract and will not allow these to be instantiated. For example, in Java, the keyword abstract is used. In C++, an abstract class is a class having at least one abstract method (a pure virtual function in C++ parlance). C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language.
Some languages, notably Java, additionally support a variant of abstract classes called an interface. An interface in the Java programming language is an Abstract type that is used to specify an interface (in the generic sense of the term that classes Such a class can only contain abstract publicly-accessible methods. In this way, they are closely related - but not equivalent - to the abstract concept of interfaces described in this article.
Sealed classes
Some languages also support sealed classes. A sealed class cannot be used as a base class. For this reason, it cannot also be an abstract class. Sealed classes are primarily used to prevent derivation. They add another level of strictness during compile-time, improve memory usage, and trigger certain optimizations that improve run-time efficiency.
Local and inner classes
In some languages, classes can be declared in scopes other than the global scope. In Computer programming, scope is an enclosing context where values and expressions are associated There are various types of such classes.
One common type is an inner class or nested class, which is a class defined within another class. Since it involves two classes, this can also be treated as another type of class association. The methods of an inner class can access static methods of the enclosing class(es). An inner class is typically not associated with instances of the enclosing class, i. e. an inner class is not instantiated along with its enclosing class. Depending on language, it may or may not be possible to refer to the class from outside the enclosing class. A related concept is inner types (a. k. a. inner data type, nested type), which is a generalization of the concept of inner classes. C++ is an example of a language that supports both inner classes and inner types (via typedef declarations). C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language.
Another type is a local class, which is a class defined within a procedure or function. This limits references to the class name to within the scope where the class is declared. Depending on the semantic rules of the language, there may be additional restrictions on local classes compared non-local ones. One common restriction is to disallow local class methods to access local variables of the enclosing function. For example, in C++, a local class may refer to static variables declared within its enclosing function, but may not access the function's automatic variables.
Metaclasses
Metaclasses are classes whose instances are classes. In object-oriented programming, a metaclass is a class whose instances are classes A metaclass describes a common structure of a collection of classes. A metaclass can implement a design pattern or describe a shorthand for particular kinds of classes. In Software engineering, a design pattern is a general reusable solution to a commonly occurring problem in Software design. Metaclasses are often used to describe frameworks. A framework is a basic conceptual structure used to solve or address complex issues
In some languages such as Python, Ruby, Java, and Smalltalk, a class is also an object; thus each class is an instance of the unique metaclass, which is built in the language. Python is a general-purpose High-level programming language. Its design philosophy emphasizes programmer productivity and code readability Ruby is a dynamic, reflective, general purpose Object-oriented programming language that combines syntax inspired by Perl with Smalltalk Smalltalk is an object-oriented, dynamically typed, reflective programming language. For example, in Objective-C, each object and class is an instance of NSObject. Objective-C is a reflective, object-oriented Programming language which adds Smalltalk -style messaging to C. The Common Lisp Object System (CLOS) provides metaobject protocols (MOPs) to implement those classes and metaclasses. Common Lisp, commonly abbreviated CL, is a dialect of the Lisp Programming language, published in ANSI standard document Information The Common Lisp Object System (CLOS is the facility for Object-oriented programming which is part of ANSI Common Lisp. In Computer science, a metaobject or meta-object is any entity that manipulates creates describes or implements other objects The object that the
Partial classes
Partial classes are classes that can be split over multiple definitions (typically over multiple files), making it easier to deal with large quantities of code. A partial class, or partial type, is a feature of some Object oriented Computer programming languages in which the declaration of a class may At compile time the partial classes are grouped together, thus logically make no difference to the output. A compiler is a Computer program (or set of programs that translates text written in a computer language (the source language) into another An example of the use of partial classes may be the separation of user interface logic and processing logic. A primary benefit of partial classes is allowing different programmers to work on different parts of the same class at the same time. They also make automatically generated code easier to interpret, as it is separated from other code into a partial class.
Partial classes have been around in Smalltalk under the name of Class Extensions for considerable time. Smalltalk is an object-oriented, dynamically typed, reflective programming language. With the arrival of the .NET framework 2, Microsoft introduced partial classes, supported in both C# 2. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer C# (pronounced C Sharp is a Multi-paradigm 0 and Visual Basic 2005. Visual Basic.NET ( VBNET) is an object-oriented Computer language that can be viewed as an evolution of Microsoft's Visual Basic
Non-class-based object-oriented programming
- See also: Object-based
To the surprise of some familiar with the use of classes, classes are not the only way to approach object-oriented programming. Another common approach is prototype-based programming. Prototype-based programming is a style of Object-oriented programming in which classes are not present and behavior reuse (known as inheritance in class-based Languages that support non-class-based programming are usually designed with the motive to address the problem of tight-coupling between implementations and interfaces due to the use of classes. For example, the Self language, a prototype-based language, was designed to show that the role of a class can be substituted by using an extant object which serves as a prototype to a new object, and the resulting language is as expressive as Smalltalk with more generality in creating objects. Self is an object-oriented programming language based on the concept of prototypes. Smalltalk is an object-oriented, dynamically typed, reflective programming language.
Examples
C++
Example 1
#include <iostream>#include <string> using namespace std;class Hello{ string what; public: Hello(const string& s) : what(s) { } void say() { cout << "Hello " << what << "!" << endl; }}; int main( int argc, char** argv ){ Hello hello_world("world"); hello_world. say(); return 0;}
This example shows how to define a C++ class named "Hello". C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language. It has a private string attribute named "what", and a public method named "say".
Example 2
class MyAbstractClass{public: virtual void MyVirtualMethod() = 0;}; class MyConcreteClass : public MyAbstractClass{public: void MyVirtualMethod() { //do something }};
An object of class MyAbstractClass cannot be created because the function MyVirtualMethod has not been defined (the =0 is C++ syntax for a pure virtual function, a function that must be part of any derived concrete class but is not defined in the abstract base class. The MyConcreteClass class is a concrete class because its functions (in this case, only one function) have been declared and implemented.
Example 3
#include <string>#include <iostream> using namespace std; class InetMessage{ string m_subject, m_to, m_from; public: InetMessage (const string& subject, const string& to, const string& from) : m_subject(subject), m_to(to), m_from(from) { } string subject () const { return m_subject; } string to () const { return m_to; } string from () const { return m_from; } virtual void printTo(ostream &out) { out << "Subject: " << m_subject << endl; out << "From: " << m_from << endl; out << "To: " << m_to << endl; }};
Java
Example 1
public class Example1{ // This is a Java class, it automatically extends the class Object public static void main (String args[]) { System. out. println("Hello world!"); }}
This example shows a simple hello world program. A "Hello World" program is a Computer program that prints out "Hello world!" on a Display device.
Example 2
public class Example2 extends Example1{ // This is a class that extends the class created in Example 1. protected int data; public Example2() { // This is a constructor for the class. It does not have a return type. data = 1; } public int getData() { return data; } public void setData(int d) { data = d; }}
This example shows a class that has a defined constructor, one member data, an accessor method (getData) and a Modifier method (setData) for that member data. It extends the previous example's class. Note that in Java all classes automatically extend the class Object. This allows you to write generic code to deal with objects of any type.
Visual Basic . NET
Example 1
Class Hello Private what as String Sub New( ByVal s as String ) what = s End Sub Sub Say() MessageBox. Show("Hello " & what ) End SubEnd Class Sub Main() Dim h as new Hello( "Foobar" ) h. Say()End Sub
This example is a port of the C++ example above. It demonstrates how to make a class named Hello with a private property named what. It also demonstrates the proper use of a constructor, and has a public method named Say. It also demonstrates how to instantiate the class and call the Say method.
PHP
Example 1
<?phpclass A { public function foo() { if (isset($this)) { echo '$this is defined ('; echo get_class($this); echo ")\n"; } else { echo "\$this is not defined. \n"; } }}?>
Example 2
<?php class DateObject { public function getTime() { /** For E_STRICT mode: * * date_default_timezone_set('CET'); */ return(time()); } public function getDate() { return(date('jS F, Y', $this->getTime()); } }?>
C#
Example 1
using System; public class Program{ public static void Main(string[] args) { System. Console. WriteLine("Hello world!"); }}
This example demonstrates a traditional "Hello world!" example in Microsoft's C# language. The Program class contains a single static method, Main(), which calls System. Console. WriteLine to print text onto the console.
Example 2
using System; public class Hello{ private string what; public Hello(string s) { what = s; } public void Say() { Console. WriteLine("Hello " + what + "!"); }} public class Program{ public static void Main(string[] args) { Hello helloWorld = new Hello("world"); helloWorld. Say(); // prints "Hello world!" onto the console }}
This is another port of the above C++ example. A class called Hello is created with a constructor that takes a string parameter. When the Say() method is called, the instance of Hello will print "Hello {what}!" onto the console. Notice that the Main() method (the entry point) is actually contained in a class itself.
ActionScript
Example 1
class Cart { private var cart:Array; public function Cart() { this. cart = new Array(); } public function addItem(id:Number, name:String):Void { this. cart. push([id, name]); } public function removeItemById(id:Number):Void { var ln:Number = this. cart. length; for (var i:Number = 0; i<ln; i++) { var curr:Array = this. cart[i]; if (curr[0] == id) this. cart. splice(i, 1); } } public function removeItemByName(name:String):Void { var ln:Number = this. cart. length; for (var i:Number = 0; i<ln; i++) { var curr:Array = this. cart[i]; if (curr[1] == name) this. cart. splice(i, 1 ); } }}
Ruby
Example 1
class Hello def self. hello string = "Hello world!" return string endend
A Ruby class "Hello", with one method "hello". This method returns the variable "string", which is set to "Hello world!".
See also
Literature
- Meyer, B. In Computer science 's Object-oriented programming, the mapped relationships of sub- and superclasses is known as a Hierarchy. the Unified Modeling Language (UML a class diagram is a type of static structure diagram that describes the structure of a system by showing the system's classes Class-based programming, or more commonly class-orientation, refers to the style of Object-oriented programming in which inheritance is achieved by defining classes : "Object-oriented software construction", 2nd edition, Prentice Hall, 1997, ISBN 0-13-629155-4
- Rumbaugh et al. : "Object-oriented modeling and design", Prentice Hall, 1991, ISBN 0-13-630054-5
- ISO/IEC 14882:2003 Programming Language C++, International standard
- Abadi; Cardelli: A Theory of Objects
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