Functional programming, a buzz word these days. Everyone is trying to learn it. A few functional programming languages are getting attraction and are getting used in the production too such as Scala, Haskell, Clojure and so on. And Even Java has already introduced a few concepts to support functional programming which are Lambdas, Functional Interfaces, Streams, etc. Now the question comes, why should a Java programmer needs to shift towards functional programming. Java has a very big community and using imperative programming from the last 2 decades. It needs a very solid reason to shift towards the functional programming paradigm. The functional programming paradigm focuses on some key concepts like immutability, higher-order functions and so on and it has a moderate learning curve, but if we can get benefit out of it, then there is no harm in learning functional. In this talk we will see, what are the benefits we get when we follow the functional programming paradigm in Java, how it makes the developer life easy. We will discuss the comparison between the imperative code vs functional code with some examples. We will discuss the transition from imperative coding to functional coding with some code examples. This talk will be good for the people who really want to switch to functional programming and want to know how to use that in Java.

1. Why should a Java programmer
shift towards
Functional Programming Paradigm
Presented By :
Rishi Khandelwal
Lead Software Consultant
Knoldus Inc

2. ● My Journey
● Functional Programming definition
● Functional Programming Features
● Imperative vs Declarative
● Optional
● Code examples
Agenda

3. My journey

4. As per wiki -
“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.”
Functional Programming Definition

5. Functional Programming Features

6. An immutable object is one whose state cannot be modified after it is
created.
An immutable variable is one that can’t change its value.
Shared state is fine if it is immutable. Mutable state is fine if it is not
shared.
Immutability

7. Imperative:
Immutability

8. Imperative:
Functional:
Immutability

9. Imperative:
Declarative

10. Imperative:
Functional:
Declarative

11. ● Returns the same output for same input values
● Has no side effects
Pure Functions

12. Pure function ?
Pure Functions

13. Pure function ? NO
Pure Functions

14. Pure lambda expression ?
Pure Functions

15. Pure lambda expression ? NO
Pure Functions

16. Pure lambda function ?
Pure Functions

17. ● Function as first class citizens
● Pass function as argument
● Return function from a function.
High Order Functions

18. Closures are nothing but stateful functions!
A few definitions from the web include:
● A closure is a combination of a function bundled together
(enclosed) with references to its surrounding state
● A closure gives you access to an outer function’s scope from an
inner function
Closures

19. Don’t evaluate immediately, evaluate when it is
needed.
Example:
● && , ||
● ? :
● Lambdas
Lazy evaluation

20. Should we use Functional
Programming in Java ?

21. ● Easy to read and understand
● Easy to maintain
● Easy to reason
● Less error prone
● Improve testability
● Easy to parallelize
Yes, ofcourse

22. Imperative vs Declarative
● How | What
● Mutate | Transform
● Side effect | Pure
● Pass Objects | Pass functions
● Hard to compose | Function composition
● Eager Evaluation | Lazy evaluation
Imperative vs Declarative

23. ● A new class introduced in java.util package
● Makes code more readable
● Null checks are not required.
● No more NullPointerException at run-time.
● No more Boilerplate code
Optional

24. Some useful methods:
● of()
● ofNullable()
● empty();
● ifPresent()
● isPresent()
● map()
● filter()
● flatMap()
● orElse()
Optional

25. Let’s see few more examples

26. 26
Thank You

27. rishi@knoldus.com
@rishckt
https://www.linkedin.com/in/rishckt/
Stay in touch