In
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 practical disciplines (includin ...
, a container is a
class or a
data structure
In computer science, a data structure is a data organization, management, and storage format that is usually chosen for Efficiency, efficient Data access, access to data. More precisely, a data structure is a collection of data values, the rel ...
[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 ...
(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 l ...
s.
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
In computing, associative containers refer to a group of class templates in the standard library of the C++ programming language that implement ordered associative arrays. Being templates, they can be used to store arbitrary elements, such as ...
are used in programming languages as class templates.
Container abstract data types include:
*
FIFO queues
*
LIFO stacks
*
Priority queues
*
Lookup tables (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 whi ...
s
*
Binary search tree
In computer science, a binary search tree (BST), also called an ordered or sorted binary tree, is a rooted binary tree data structure with the key of each internal node being greater than all the keys in the respective node's left subtree and ...
s (BSTs), particularly
self-balancing BSTs
*
Hash tables
Graphic containers
Widget toolkit
A widget toolkit, widget library, GUI toolkit, or UX library is a library or a collection of libraries containing a set of graphical control elements (called ''widgets'') used to construct the graphical user interface (GUI) of programs.
Most wid ...
s 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 ...
,
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 ...
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 types (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
In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point valu ...
:;
Templates or
Generics
:: Ensures reusability and type safety; may be thought as a reverse inheritance. However, this approach may require implementing a
template specialization which is reputedly a time-consuming process given that types differ in their methods.
See also
*
List of data structures
*
Standard Template Library#Containers
*
Collection (abstract data type)
*
Stack data structure
In computer science, a stack is an abstract data type that serves as a collection of elements, with two main operations:
* Push, which adds an element to the collection, and
* Pop, which removes the most recently added element that was not y ...
*
Java ConcurrentMap
References
External links
Container Data Structure Declaration and Initialization
{{DEFAULTSORT:Container (Data Structure)
Abstract data types
Object-oriented programming
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pt:Container (programação)
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