What is a first class citizen function?

Question

What is a first class citizen function?

Does Java supports first class citizen function?

Edit:
As mention on Wikepedia

F

Answer 1

The above answers for @Alpine questions are mostly defining what is First Class Functions along with examples. But still, one question remains why to use?

I'll try to answer the benefits a little differently in Scala where first-class functions are used further as higher-order functions(map, flatMap), Partially Applied Functions and Currying:

1. As we focus on declarative programming, the how part of processing the data is left as an implementation detail to map, flatMap, and focused more on handling the what actual logic flow. A caller can specify what should be done and leave the higher-order functions to handle the actual logic flow.

2. Partially Applied Functions and Currying: What if you wanted to reuse a function invocation and retain some of the parameters to avoid typing them in again?

Partially Applied Function Example:

def factorOf(x: Int, y: Int) = y % x == 0
val multipleOf3 = factorOf(3, _: Int)
val y = multipleOf3(78)

Currying Example:

def factorOf(x: Int)(y: Int) = y % x == 0
val isEven = factorOf(2) _
val z = isEven(32)

The above examples show you how you can reuse the part of first-class functions by not passing all parameters and keep your code DRY principle. These are few benefits for using first-class functions

Reference for more details: https://www.oreilly.com/library/view/learning-scala