computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...

, a container is a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

or a

data structure In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...

Entry ''data structure'' in the

Encyclopædia Britannica The (Latin for "British Encyclopædia") is a general knowledge English-language encyclopaedia. It is published by Encyclopædia Britannica, Inc.; the company has existed since the 18th century, although it has changed ownership various time ...

(2009
Online entry
Accessed 4 Oct 2011. whose instances are collections of other objects. In other words, they store objects in an organized way that follows specific access rules. The size of the container depends on the number of objects (elements) it contains. Underlying (inherited) implementations of various container types may vary in size, complexity and type of language, but in many cases they provide flexibility in choosing the right implementation for any given scenario. Container data structures are commonly used in many types of

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

Function and properties

Containers can be characterized by the following three properties: * ''access'', that is the way of accessing the objects of the container. In the case of arrays, access is done with the array index. In the case of stacks, access is done according to the LIFO (last in, first out) order and in the case of queues it is done according to the FIFO (first in, first out) order; * ''storage'', that is the way of storing the objects of the container; * ''traversal'', that is the way of traversing the objects of the container. Container classes are expected to implement CRUD-like methods to do the following: * create an empty container (constructor); * insert objects into the container; * delete objects from the container; * delete all the objects in the container (clear); * access the objects in the container; * access the number of objects in the container (count). Containers are sometimes implemented in conjunction with iterators.

Types

Containers may be classified as either ''single-value containers'' or ''associative containers''. Single-value containers store each object independently. Objects may be accessed directly, by a language loop construct (e.g. for loop) or with an iterator. An associative container uses an associative array, map, or dictionary, composed of key-value pairs, such that each key appears at most once in the container. The key is used to find the value, the object, if it is stored in the container. Associative containers are used in programming languages as class templates. Container abstract data types include: * FIFO queues * LIFO stacks *

Priority queue In computer science, a priority queue is an abstract data-type similar to a regular queue or stack data structure in which each element additionally has a ''priority'' associated with it. In a priority queue, an element with high priority is se ...

s *

Lookup table In computer science, a lookup table (LUT) is an array that replaces runtime computation with a simpler array indexing operation. The process is termed as "direct addressing" and LUTs differ from hash tables in a way that, to retrieve a value v wi ...

s (LUTs) * Key-associated data structures ** Sets, containing and indexing objects by value or by specific property; ** Maps, associating to each key a "value" for lookup Common data structures used to implement these abstract types include: * Arrays and their derivatives *

Linked list In computer science, a linked list is a linear collection of data elements whose order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a collection of nodes whic ...

s * Binary search trees (BSTs), particularly self-balancing BSTs * Hash tables

Graphic containers

Widget toolkits also use containers, which are special widgets to group other widgets, such as

windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

, panels. Apart from their graphical properties, they have the same type of behavior as container classes, as they keep a list of their child widgets, and allow adding, removing, or retrieving widgets among their children.

In statically-typed languages

Container abstractions can be written in virtually any programming language, regardless of its type system. However, in strongly-typed

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 pr ...

languages it may be somewhat complicated for a developer to write reusable homogeneous containers. Because of differences in element types this results in a tedious process of writing and keeping a collection of containers for every elemental type. Many elemental types (e.g. integers or floating numbers) are inherently incompatible with each other because of the memory size they occupy and their semantic meaning and therefore require different containers (unless of course, they are mutually compatible or convertible). Modern programming languages offer various approaches to help solving the problem: :; Universal basic type :: A type that is universally assignable by any other (e.g. root Object class). :; Downcasting; :;Class substitution :: Previous three approaches above are used for weakly typed languages; these usually imply inheritance and polymorphism shared by types. :;

Union type In computer science, a union is a value that may have any of several representations or formats within the same position in memory; that consists of a variable that may hold such a data structure. Some programming languages support special data t ...

s (C/C++ language) :: Permits storing types of different data sizes; it is hard to ensure which type is stored in a union upon retrieval however and should be carefully followed. :; Type conversion :;

Template Template may refer to: Tools * Die (manufacturing), used to cut or shape material * Mold, in a molding process * Stencil, a pattern or overlay used in graphic arts (drawing, painting, etc.) and sewing to replicate letters, shapes or designs Co ...

s or

Generic Generic or generics may refer to: In business * Generic term, a common name used for a range or class of similar things not protected by trademark * Generic brand, a brand for a product that does not have an associated brand or trademark, other ...

s :: Ensures reusability and type safety; may be thought as a reverse inheritance. However, this approach may require implementing a

template specialization Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered by ...

which is reputedly a time-consuming process given that types differ in their methods.

References

External links