At least since the release of Java 8, functional programming has become mainstream in the Java community. Things like collection processing, lazy evaluation and concurrent programming are much easier to describe in a functional style than in the traditional procedural or object-oriented way. Xtend is a Java dialect hosted at Eclipse. Designed to remove the syntactic noise, it offers a superior syntax and additional abstractions to provide the full power of functional programming to Java developers. As it compiles to Java 5 code, it will enable functional programming even for Android and GWT developers. In this tutorial, you will learn the basic principles of functional programming and the Xtend idioms to write code the functional way: concise, easy to understand, and yet powerful. No prior knowledge of functional programming or Xtend required.

1. Functional Programming with
Jan Köhnlein & Sven Efftinge

2. Functional programming is like
describing your problem to a mathematician.
Imperative programming is like
giving instructions to an idiot.

3. Imperative vs Functional
State Changes vs No State Change
How? vs What?

4. 2 Important Principles

5. #1 : No Side-Effects

6. Haskell is a purely-functional programming language

7. Most other functional programming languages
are more relaxed, i.e. non-pure.

8. Most other functional programming languages
are more relaxed, i.e. non-pure.
But still embrace immutability!

9. Why Immutability?
Thread-Safety
Easy to test, construct and use
Good Map keys and Set members
Code is easier to read and understand

10. Java and
Immutability

11. The beauty of
java.lang.String
Thread-Safety
Easy to test, construct and use
Good Map keys and
Set members
Code is easier to read
and understand

12. "Classes should be immutable
unless there's a very good reason
to make them mutable...”
(Joshua Bloch)

13. "When you create immutable classes,
entire categories of problems simply
disappear.”
(javapractices.com)

14. How to build an
immutable data type in Java?
make everything final
create constructor for fields
implement hashcode
implement equals

15. writing Immutable code in Java
is tedious & error-prone

16. Immutability in
final by default
val vs. var
immutable collection literals
everything is an expression
@Pure
@Data

17. First Exercise
Immutable Data Types

18. 2 Important Principles

19. #2 : First-Class Functions

20. #2 : First-Class Functions
passing functions as arguments
higher-order functions
lambdas

21. An Example

23. @Data class Movie {
String title
int year
double rating
long numberOfVotes
ImmutableSet<String> categories
}

24. What’s the best drama of the 70ies?

25. The imperative way

28. The functional way

29. Java 8
Lambdas

30. Lambdas

32. Second Exercise
In The Movies

33. Use the force, Duke!
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