What Is Functional Programming In Java
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In computer science, functional programming is a programming paradigm—a style of building the structure and elements of computer programs—that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. It is a declarative programming paradigm in that programming is done with expressions or declarations[1] instead of statements. In functional code, the output value of a function depends only on its arguments, so calling a function with the same value for an argument always produces the same result. This is in contrast to imperative programming where, in addition to a function's arguments, global program state can affect a function's resulting value. One of the key motivations for the development of functional programming is making a program easier to understand by eliminating changes in state that do not depend on function inputs which are called side effects.
Functional programming has its origins in lambda calculus, a formal system developed in the 1930s to investigate computability, the Entscheidungsproblem, function definition, function application, and recursion. Many functional programming languages can be viewed as elaborations on the lambda calculus. Another well-known declarative programming paradigm, logic programming, is based on relations.[2]
In contrast, imperative programming changes state with statements in the source code, the simplest example being assignment. Imperative programming has subroutines, but these are not mathematical functions. They can have side effects that may change a program's state, allowing for functions without return values. Because of this, they lack referential transparency, that is, the same language expression can result in different values at different times depending on the state of the executing program.[2]
Functional programming languages have largely been emphasized in academia rather than industry settings. However, programming languages that support functional programming have been used in industry, including Common Lisp, Scheme,[3][4][5][6] Clojure, Wolfram Language,[7][8] Racket,[9] Erlang,[10][11][12] OCaml,[13][14] Haskell,[15][16] and F#.[17][18] JavaScript, one of the world's most widely distributed languages,[19][20][21] has the properties of a dynamically typed functional language,[20] in addition to imperative and object-oriented paradigms. Functional programming is also key to some languages that have found success in specific domains, like R in statistics,[22][23] J, K and Q in financial analysis, and XQuery/XSLT for XML.[24][25] Domain-specific declarative languages like SQL and Lex/Yacc use some elements of functional programming, especially in not supporting mutable values.[26]
Programming in a functional style can be accomplished in languages that are not specifically designed for functional programming, such as with Perl,[27] PHP,[28] C++11, and Kotlin.[29] A hybrid case is that of Scala[30] – it is frequently written in a functional style, but the presence of side effects and mutable state place it in a grey area between imperative and functional languages.
Functional programming is a paradigm that allows programming using expressions i.e. declaring functions, passing functions as arguments and using functions as statements (rightly called expressions in Java8).