Container (data structure)

For the abstract notion of containers in Type theory, see Container (Type theory).

In computer science, a container is a class, a data structure^[1][2], or an abstract data type (ADT) whose instances are collections of other objects. In other words; they are used for storing objects in an organized way following specific access rules. The size of the container depends on the number of the objects (elements) it contains.The underlying implementation of various types of containers may vary in space and time complexity allowing for flexibility in choosing the right implementation for a given scenario.

Overview

Container can be studied under three points of views.

1. Access : It means accessing the container elements. In case of arrays accessing is done using array index. For Stacks, access of elements is done using LIFO (Last In First Out)^[3] and in Queues it is done using FIFO (First In First Out)^[4][3].

2. Storage : It includes storing of items of containers. Some containers are finite containers and some are infinite containers.

3. Traversal : It includes how the item can be traversed.

Container classes are expected to implement methods to do the following:

• create a new empty container (constructor),
• report the number of objects it stores (size),
• delete all the objects in the container (clear),
• insert new objects into the container,
• remove objects from it,
• provide access to the stored objects.

Containers are sometimes implemented in conjunction with iterators.

Types

There are two types of containers:

1. Value based containers
2. Reference based containers

Value based containers

store copies of objects.If we access an object, an object returns a copy of it. If external object is changed after it has been inserted in container will not affect the content of the container.

Reference based containers

store pointers and references to the object. If we access an object, an object returns reference to it.If external object is changed after it has been inserted in container, affect the content of the container.

Examples of containers

Containers are divided in the Standard Template Library into associative containers and standard sequence containers. Besides this two types, so-called container adaptors exist. Data structures that implement containers include arrays, lists, maps, queues, sets, stacks, tables, trees, and vectors.

Graphic containers

Widget toolkits use special widgets also called Containers to group the other widgets together (windows, 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 to add, remove, or retrieve widgets amongst their children.

Containers in Object oriented programming

In object oriented programming, we define a container class as class capable of storing other objects.These classes usually implement some kind of data structure such as map, set, stacks etc.The size of the collection of objects is adjusted automatically in a container class.

Implementations

• Java: Java collections framework (JCF)
• C++: C++ Standard Library (SC++L) or the obsolete Standard Template Library (STL)
• .NET: System.Collections (MSDN)
• ActionScript3: AS3Commons Collections Framework
• Objective-C: part of the Foundation Kit

See also

• List of data structures
• Standard Template Library#Containers
• Collection (computing)
• Stack data structure

References

1. ^ Paul E. Black (ed.), entry for data structure in Dictionary of Algorithms and Data Structures. U.S. National Institute of Standards and Technology.15 December 2004. Accessed on Oct 04, 2011.
2. ^ Entry data structure in the Encyclopædia Britannica (2009) Online entry Accessed on Oct 04, 2011.
3. ^ ^{a b} LIFO(investopedia.com)
4. ^ FIFO(businessdictionary.com)

External Links

• Container Data Structure Declaration and Initialization
• Container data structures