computer programming Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...

, a collection is an

abstract data type In computer science, an abstract data type (ADT) is a mathematical model for data types, defined by its behavior (semantics) from the point of view of a '' user'' of the data, specifically in terms of possible values, possible operations on data ...

that is a grouping of items that can be used in a polymorphic way. Often, the items are of the same

data type In computer science and computer programming, a data type (or simply type) is a collection or grouping of data values, usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these ...

such as int or

string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

. Sometimes the items derive from a common type; even deriving from the most general type of a

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

such as

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an a ...

or variant. Although easily confused with implementations in programming languages, collection, as an abstract concept, refers to mathematical concepts which can be misunderstood when the focus is on an implementation. For example, a priority queue is often implemented as a heap, while an associative array is often implemented as a hash table, so these abstract types are often referred to by this preferred implementation, as a "heap" or a "hash", though this is incorrect conceptually.

Subtypes

Other abstract data types are more specific than collection.

Linear

Some collections maintain a linear ordering of items with access to one or both ends. The data structure implementing such a collection need not be linear. For example, a priority queue is often implemented as a heap, which is a kind of tree. Notable linear collections include: *

list A list is a Set (mathematics), set of discrete items of information collected and set forth in some format for utility, entertainment, or other purposes. A list may be memorialized in any number of ways, including existing only in the mind of t ...

stack Stack may refer to: Places * Stack Island, an island game reserve in Bass Strait, south-eastern Australia, in Tasmania’s Hunter Island Group * Blue Stack Mountains, in Co. Donegal, Ireland People * Stack (surname) (including a list of people ...

* queue *

priority queue In computer science, a priority queue is an abstract data type similar to a regular queue (abstract data type), queue or stack (abstract data type), stack abstract data type. In a priority queue, each element has an associated ''priority'', which ...

double-ended queue In computer science, a double-ended queue (abbreviated to deque, ) is an abstract data type that generalizes a queue, for which elements can be added to or removed from either the front (head) or back (tail). It is also often called a head-t ...

double-ended priority queue In computer science, a double-ended priority queue (DEPQ)set Set, The Set, SET or SETS may refer to: Science, technology, and mathematics Mathematics *Set (mathematics), a collection of elements *Category of sets, the category whose objects and morphisms are sets and total functions, respectively Electro ...

multiset In mathematics, a multiset (or bag, or mset) is a modification of the concept of a set that, unlike a set, allows for multiple instances for each of its elements. The number of instances given for each element is called the ''multiplicity'' of ...

associative array In computer science, an associative array, key-value store, map, symbol table, or dictionary is an abstract data type that stores a collection of (key, value) pairs, such that each possible key appears at most once in the collection. In math ...

graph Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties *Graph (topology), a topological space resembling a graph in the sense of discret ...

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

A set can be interpreted as a specialized multiset, which in turn is a specialized associative array, in each case by limiting the possible values—considering a set as represented by its

indicator function In mathematics, an indicator function or a characteristic function of a subset of a set is a function that maps elements of the subset to one, and all other elements to zero. That is, if is a subset of some set , then the indicator functio ...

Implementation

As an abstract data type, collection does not prescribe an implementation, though

type theory In mathematics and theoretical computer science, a type theory is the formal presentation of a specific type system. Type theory is the academic study of type systems. Some type theories serve as alternatives to set theory as a foundation of ...

describes implementation considerations. Some collection types are provided as

primitive data type In computer science, primitive data types are a set of basic data types from which all other data types are constructed. Specifically it often refers to the limited set of data representations in use by a particular processor, which all compiled ...

s in a language, such as lists, while more complex collection types are implemented as

composite data type In computer science, a composite data type or compound data type is a data type that consists of programming language scalar data types and other composite types that may be heterogeneous and hierarchical in nature. It is sometimes called a struct ...

s in libraries, sometimes in a language's

standard library In computer programming, a standard library is the library (computing), library made available across Programming language implementation, implementations of a programming language. Often, a standard library is specified by its associated program ...

. Examples include: * C++: known as ''containers'', implemented in

C++ Standard Library The C standard library, sometimes referred to as libc, is the standard library for the C programming language, as specified in the ISO C standard.ISO/ IEC (2018). '' ISO/IEC 9899:2018(E): Programming Languages - C §7'' Starting from the origina ...

and earlier

Standard Template Library The Standard Template Library (STL) is a software library originally designed by Alexander Stepanov for the C++ programming language that influenced many parts of the C++ Standard Library. It provides four components called ''algorithms'', '' ...

* Java: implemented in the

Java collections framework The Java collections framework is a set of classes and interfaces that implement commonly reusable collection data structures. Although referred to as a framework, it works in a manner of a library. The collections framework provides both inte ...

* Oracle

PL/SQL PL/SQL (Procedural Language for SQL) is Oracle Corporation's procedural extension for SQL and the Oracle relational database. PL/SQL is available in Oracle Database (since version 6 - stored PL/SQL procedures/functions/packages/triggers sinc ...

implements collections as programmer-defined types * Python: some built-in, others implemented in th
collections
library *

.NET The .NET platform (pronounced as "''dot net"'') is a free and open-source, managed code, managed computer software framework for Microsoft Windows, Windows, Linux, and macOS operating systems. The project is mainly developed by Microsoft emplo ...

provides the and interfaces and implementations such as . *

Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...

provides the and structs in the namespace.

References

External links

Apache Commons Collections

AS3Commons Collections Framework
ActionScript3 implementation of the most common collections.
CollectionSpy
— A profiler for Java's Collections Framework.
Guava

Mango Java library
{{DEFAULTSORT:Collection Abstract data types