Functional Programming with

Jan Köhnlein & Sven Efftinge

Functional programming is like describing your problem to a mathematician.

Imperative programming is like

giving instructions to an idiot.

Imperative vs Functional

How? vs What?State Changes vs No State Change

2 Important Principles

#1 : No Side-Effects

Haskell is a purely-functional programming language

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

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

But still embrace immutability!

Why Immutability?

Thread-Safety

Easy to test, construct and use

Good Map keys and Set members

Code is easier to read and understand

Java and Immutability

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

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

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

How to build an immutable data type in Java?

make everything final

create constructor for fields

implement hashcode

implement equals

writing Immutable code in Java is tedious & error-prone

Immutability infinal by default

val vs. var

immutable collection literals

everything is an expression

@Pure

@Data

First ExerciseImmutable Data Types

2 Important Principles

#2 : First-Class Functions

#2 : First-Class Functions

passing functions as arguments higher-order functions

lambdas

An Example

@Data class Movie {String titleint yeardouble ratinglong numberOfVotesImmutableSet<String> categories

}

What’s the best drama of the 70ies?

The imperative way

The functional way

Java 8 Lambdas

Lambdas

Second Exercise In The Movies

Use the force, Duke!

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