Java : Functional Programming-Introduction

Functional programming is a programming style in which computations are codified as functional programming functions. These are mathematical function-like constructs (e.g., lambda functions) that are evaluated in expression contexts.

Functional programming languages are declarative, meaning that a computation's logic is expressed without describing its control flow. In declarative programming, there are no statements. Instead, programmers use expressions to tell the computer what needs to be done, but not how to accomplish the task. If you are familiar with SQL or regular expressions, then you have some experience with the declarative style; both use expressions to describe what needs to be done, rather than using statements to describe how to do it.

A computation in functional programming is described by functions that are evaluated in expression contexts. These functions are not the same as the functions used in imperative programmings, such as a Java method that returns a value. Instead, a functional programming function is like a mathematical function, which produces an output that typically depends only on its arguments. Each time a functional programming function is called with the same arguments, the same result is achieved. Functions in functional programming are said to exhibit referential transparency. This means you could replace a function call with its resulting value without changing the computation's meaning.