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In computer science, the object lifetime (or life cycle) of an object in object-oriented programming is the time between an object's creation (also known as instantiation or construction) till the object is no longer used, and is destructed or freed. Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ...
An object is fundamental concept in object-oriented programming. ...
Object-oriented programming (OOP) is a programming paradigm that uses objects to design applications and computer programs. ...
In object-oriented programming (OOP), the meaning of creating objects is far more subtle than simple allocating of spaces for variables. First, this is due to the fact that, in the OOP paradigm, the lifetime of each object tends to vary more widely than in the case in conventional programming. There are a lot of subtle questions, including whether the object be considered alive in the process of creation, and concerning the order of calling initializing code. In some sense, the creation can happen before the beginning of the program when objects are placed in a global scope.
Creating objects
In a typical case, the process is as follows: - calculate the size of an object - the size is mostly the same as that of the class but can vary. When the object in question is not derived from a class, but from a prototype instead, the size of an object is usually that of the internal data structure (a hash for instance) that holds its slots.
- allocation - allocating memory space with the size of an object plus the growth later, if possible to know in advance
- binding methods - this is usually either left to the class of the object, or is resolved at dispatch time, but nevertheless it is possible that some object models bind methods at creation time
- calling an initializing code (namely, constructor) of superclass
- calling an initializing code of class being created
Those tasks can be completed at once but are sometimes left unfinished and the order of the tasks can vary and can cause several strange behaviors. For example, in multi-inheritance, which initializing code should be called first is a difficult question to answer. However, superclass constructors should be called before subclass constructors. In object-oriented programming, a class is a programming language construct that is used to group related instance variables and methods. ...
Prototype-based programming is a style and subset of object-oriented programming in which classes are not present, and behaviour reuse (known as inheritance in class-based languages) is done by cloning existing objects which serve as prototypes for the new ones. ...
Some programming languages allow multiple inheritance, in which a class can inherit behaviors and features from more than one superclass. ...
It is a complex problem to create each object as an element of an array. Some languages (e.g. C++) leave this to programmers.
Handling exceptions in the midst of creation of an object is particularly problematic because usually the implementation of throwing exceptions relies on valid object states. For instance, there is no way to allocate a new space for an exception object when the allocation of an object failed before that due to a lack of free space on the memory. Due to this, implementations of OO languages should provide mechanisms to allow raising exceptions even when there is short supply of resources, and programmers or the type system should ensure that their code is exception-safe. Note that propagating an exception is likely to free resources (rather than allocate them). However, in object oriented programming, object construction may always fail, because constructing an object should establish the class invariants, which are often not valid for every combination of constructor arguments. Thus, constructors can always raise exceptions. Exception handling is a programming language construct or computer hardware mechanism designed to handle the occurrence of some condition that changes the normal flow of execution. ...
Exception handling is a programming language mechanism designed to handle runtime errors or other problems (exceptions) inside a computer program. ...
This article is about class invariants in computer science; for use of the term in mathematics, see equivalence class and invariant. ...
The abstract factory pattern is a way to decouple a particular implementation of an object from code for the creation of such an object. A software design pattern, the Abstract Factory Pattern provides a way to encapsulate a group of individual factories that have a common theme. ...
Creation methods The way to create objects varies across languages. In some class-based languages, a special method known as a constructor, is responsible for validating the state of an object. Just like ordinary methods, constructors can be overloaded in order to make it so that an object can be created with different attributes specified. Also, the constructor is the only place to set the state of immutable objects. A copy constructor is a constructor which takes a (single) parameter of an existing object of the same type as the constructor's class, and returns a copy of the object sent as a parameter. In object-oriented programming, a constructor (sometimes shorted to ctor) in a class is a special block of statements called when an object is created, either when it is declared (statically constructed on the stack, possible in C++ but not in Java and other object-oriented languages) or dynamically constructed...
Method overloading is a feature found in various programming languages such as C++ and Java that allows the creation of several functions with the same name which differ from each other in terms of the type of the inbananaput and the type of the output of the function. ...
In computer science, an immutable object, as opposed to a mutable object, is a kind of object whose internal states cannot be modified after it is created. ...
Other programming languages, such as Objective-C, have class methods, which can include constructor-type methods, but are not restricted to merely instantiating objects. Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language...
C++ and Java have been criticized for not providing named constructors. This can be problematic, for instance, when a programmer wants to provide ways to create a point object either from cartesian coordinate or from the polar coordinate--because both coordinates would be represented by two integers. Objective-C can circumvent this problem, in that the programmer can create a Point class, with initialization methods, for example, +newPointWithX:andY:, and +newPointWithR:andTheta:. Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ...
This article describes some of the common coordinate systems that appear in elementary mathematics. ...
A constructor can also refer to a function which is used to create a value of a tagged union, particularly in functional languages. In computer science, a tagged union, also called a variant, variant record, discriminated union, or disjoint union, is a data structure used to hold a value that could take on several different, but fixed types. ...
Destroying objects It is generally the case that after an object is used, it is removed from memory to make room for other programs or objects to take that object's place. In order for this to happen, a destruction method is called upon that object. Destroying an object will cause any references to the object to become invalid. In general, a reference is something that refers to or designates something else, or acts as a connection or a link between two things. ...
A destructor is a method called when an instance of a class is deleted, before the memory is deallocated. Note that in C++, a destructor can not be overloaded like a constructor can. It has to have no arguments. A destructor does not need to maintain class invariants. In object-oriented programming, a destructor (sometimes shortened to dtor) is a method which is automatically invoked when the object is destroyed. ...
Used mainly in object-oriented programming, the term method refers to a piece of code that is exclusively associated either with a class (called class methods, static methods, or factory methods) or with an object (called instance methods). ...
This article or section does not cite any references or sources. ...
In computer programming, a class invariant is an invariant used to constrain objects of a class. ...
In garbage collecting languages, objects may be destroyed when they can no longer be reached by the running code. Examples of this are Python and Java. Python has destructors, and they are optional. In many garbage collecting languages, finalizers (which are called before an object is garbage-collected) are used instead of destructors, since the point of garbage-collection is not predictable in these languages. Example of these include Java and Ruby. In computer science, garbage collection (also known as GC) is a form of automatic memory management. ...
Python is a high-level programming language first released by Guido van Rossum in 1991. ...
Java is a programming language originally developed by Sun Microsystems and released in 1995. ...
In object-oriented programming languages that use automatic garbage collection, a finalizer is a special method that is executed when an object is garbage collected. ...
Ruby is a reflective, object-oriented programming language. ...
Examples
class Foo { // This is the prototype of the constructors public: Foo(int x); Foo(int x, int y); // Overloaded Constructor Foo(const Foo &old); // Copy Constructor ~Foo(); // Destructor }; Foo::Foo(int x) { // This is the implementation of // the one-argument constructor } Foo::Foo(int x, int y) { // This is the implementation of // the two-argument constructor } Foo::Foo(const Foo &old) { // This is the implementation of // the copy constructor } Foo::~Foo() { // This is the implementation of the destructor } int main() { Foo foo(14); // call first constructor Foo foo2(12, 16); // call overloaded constructor Foo foo3(foo); // call the copy constructor return 0; // destructors called in backwards-order // here, automatically } C++ (pronounced see plus plus, IPA: ) is a general-purpose, high-level programming language with low-level facilities. ...
class Foo { public Foo(int x) { // This is the implementation of // the one-argument constructor } public Foo(int x, int y) { // This is the implementation of // the two-argument constructor } public Foo(Foo old) { // This is the implementation of // the copy constructor } public static void main(String[] args) { Foo foo = new Foo(14); // call first constructor Foo foo2 = new Foo(12, 16); // call overloaded constructor Foo foo3 = new Foo(foo); // call the copy constructor // garbage collection happens under the covers, and classes are destroyed } } Java is a programming language originally developed by Sun Microsystems and released in 1995. ...
#import <objc/Object.h> @interface Point : Object { double x; double y; } //These are the class methods; we have declared two constructors + (Point *) newWithX: (double) andY: (double); + (Point *) newWithR: (double) andTheta: (double); //Instance methods - (Point *) setFirstCoord: (double); - (Point *) setSecondCoord: (double); /* Since Point is a subclass of the generic Object * class, we already gain generic allocation and initialization * methods, +alloc and -init. For our specific constructors * we can make these from these methods we have * inherited. */ @end @implementation Point - (Point *) setFirstCoord: (double) new_val { x = new_val; } - (Point *) setSecondCoord: (double) new_val { y = new_val; } + (Point *) newWithX: (double) x_val andY: (double) y_val { //Concisely written class method to automatically allocate and //perform specific initialization. return [[[Point alloc] setFirstCoord:x_val] setSecondCoord:y_val]; } + (Point *) newWithR: (double) r_val andTheta: (double) theta_val { //Instead of performing the same as the above, we can underhandedly //use the same result of the previous method return [Point newWithX:r_val andY:theta_val]; } @end int main(void) { //Constructs two points, p and q. Point *p = [Point newWithX:4.0 andY:5.0]; Point *q = [Point newWithR:1.0 andTheta:2.28]; //...program text.... //We're finished with p, say, so, free it. //If p allocates more memory for itself, may need to //override Object's free method in order to recursively //free p's memory. But this is not the case, so we can just [p free]; //...more text... [q free]; return 0; } Objective-C, often referred to as ObjC or more seldomly as Objective C or Obj-C, is an object oriented programming language implemented as an extension to C. It is used primarily on Mac OS X and GNUstep, two environments based on the OpenStep standard, and is the primary language...
class Socket: def __init__(self, remote_host): self.connection = connectTo(remote_host) def send(self): # send data def recv(self): # receive data def f(): s = Socket('example.com') s.send('blah') return s.recv() Socket will be closed at the next garbage collection round, as all references to it have been lost. Python is a high-level programming language first released by Guido van Rossum in 1991. ...
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