Clean Lambdas & Streams in Java8

Enterprise Java Training

Victor Rentea

10 March 2017

Clean Lambdas & Streams in Java 8A Hands-on Experience

Workshop: Searching Streams (30 min)

Workshop: Transforming Streams (40 min)

Workshop: Cleaning Lambdas (20 min)

Conclusions: Best Practices (20 min)

Ag

en

da www.victorrentea.ro

victor.rentea@gmail.com

@victorrentea

© Copyright Victor Rentea 2017

VictorRentea.ro

Clean Code Evangelist

International Speaker Spring and

Clean Code, Design Patterns ( )

TDD, Coding Dojos

Java Performance

many more:

Victor Rentea, PhD(CS)Consultant, Technical Lead

Lead Architect for major client at IBM Romania

Night Job :

Freelance Trainer & Coach

victorrentea@gmail.com www.victorrentea.ro@victorrentea2

VictorRentea.ro

They are cool

Expressive code- .filter(Order::isActive)

Concise code (½ lines?)

Cryptic? Hard to read?- What guidelines to follow ?

Why Lambdas ?

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Which λ to use in enterprise Java apps ?- Readable, maintainable

- vs Java7

-

Questionnaire-based- Java8 features in examples from production

- For Java developers of any exp level (min 3 months of Java8 hands-on)

- Wanna submit you answer? Thank you !! : http://bit.ly/2dFf2fi

My own little

Clean Lambdas Study

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Workshop: Searching Streams (30 min)

Workshop: Transforming Streams (40 min)

Workshop: Cleaning Lambdas (20 min)

Conclusions: Best Practices (20 min)

Agenda

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// Cool Class Diagram[Order|id:Long;creationDate;paymentMethod;status:Status;totalPrice:BigDecimal]-orderLines*>[OrderLine|count:int;isSpecialOffer][OrderLine]-product>[Product|name]

[Audit|action;date;user;modifiedField]

Before we start: configure your IDE to suggest static imports of:java.util.stream.Collectors.* and java.util.Comparator.comparing

In Eclipse: Preferences > type “favo” > Favorites > New Type & New Member

Our Domain Model

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static method constructor

Method References

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Integer::parseInt

Order::getCreationDate

OrderMapper::toDto

String::length

myOrder::getCreationDate

orderMapper::toDto

firstName::length

Date::new

... of a class … of an instanceinstance method

instanceis known

𝒇(𝑶𝒓𝒅𝒆𝒓):𝑫𝒂𝒕𝒆

𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕

𝒇(𝑶𝒓𝒅𝒆𝒓𝑴𝒂𝒑𝒑𝒆𝒓,𝑶𝒓𝒅𝒆𝒓):𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐

𝒇(): 𝑫𝒂𝒕𝒆

𝒇(): 𝒊𝒏𝒕

𝒇 𝑶𝒓𝒅𝒆𝒓 :𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐

𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕𝒇(): 𝑫𝒂𝒕𝒆

𝒇(𝑳𝒐𝒏𝒈):𝑫𝒂𝒕𝒆

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= (String s) -> {return s.length();};

Function<String, Integer> stringLen = (String s) -> s.length(); // implicit return

= s -> s.length();

= String :: length;

Comparator<User> fNameComparator = (u1,u2)-> u1.getFName().compareTo(u2.getFName());

= Comparator.comparing(User :: getFName);

Predicate<Apple> appleIsHeavy = a -> a.getWeight() > 150;

= Apple :: isHeavy;

Consumer<String> stringPrinter = s -> System.out.println(s); // returns void

= System.out::println;

Supplier<Wine> firstMiracle = () -> new Wine();

= Wine :: new;

𝒇 𝑺𝒕𝒓𝒊𝒏𝒈 : 𝑰𝒏𝒕𝒆𝒈𝒆𝒓

𝒇 𝑼𝒔𝒆𝒓,𝑼𝒔𝒆𝒓 : 𝒊𝒏𝒕

𝒇 𝑨𝒑𝒑𝒍𝒆 : 𝒃𝒐𝒐𝒍𝒆𝒂𝒏

𝒇 𝑺𝒕𝒓𝒊𝒏𝒈

𝒇():𝑾𝒊𝒏𝒆 ʎ syntax33

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flatMap(i -> i.getChildren().stream())

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2 4 1 3

0 2+

.reduce(0, +)

6+ 7+ 10+

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orders.stream()

.filter(Order::isActive)

.map(Order::getCreationDate)

.collect(toList())

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orders.stream()

.filter(Order::isActive)

.map(Order::getCreationDate)

.collect(toList())

Give me!Here you go!

Give me!

Give me!

Argh!Another one!

Here you go!

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.filter(Order::isActive)

orders.stream()

.map(Order::getCreationDate)

Give me! Nope! I’m done.

.collect(toList())

.limit(3)

AR

E NEV

ER SEEN

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.filter(Order::isActive)

.map(Order::getCreationDate)

.findFirst()

orders.stream() AR

E NEV

ER SEEN

I’m done.

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Short Circuiting

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The most important principle in Programming?

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ingle esponsibility rincipleS R P

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Keep It Short & SimpleK I S S

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KISS

(or nullable): SRP

Work with predicates(coming up next)

Simple code

Look for the simplest

form

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Pair Programming

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public static Predicate<Order> deliveryDueBefore(Date date) {

return order -> order.getDeliveryDueDate().before(date);

}

Clean Lambdas

Encapsulate Predicates

Predicate<Order> needsTracking = order -> order.hasPoliticalCustomer();

Set<Customer> customersToNotify = orders.stream()

.filter(order -> order.getDeliveryDueDate().before(warningDate) &&

order.getOrderLines().stream()

.anyMatch(line -> line.getStatus() != Status.IN_STOCK))

.map(Order::getCustomer)

.collect(toSet());

.filter(order -> order.getDeliveryDueDate().before(warningDate))

.filter(order -> order.getOrderLines().stream()

.anyMatch(line -> line.getStatus() != Status.IN_STOCK))(OrderLine::isNotInStock))

.filter(this::hasOrdersNotInStock)

<entity>

OrderLine

<service>

NotificationService(this)

OrderPredicates.deliveryDueBefore(warningDate))deliveryDueBefore(warningDate)).or(this::needsTracking))

<utility>

OrderPredicates

In entities

In the class needing it

As functions returning Predicates

Auxiliary Predicate variables

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Find the shortest form(peer review)

Don’t abuse them

Clean Code Using Java8 New Features(lambdas, Stream, Optional)

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Resources

Java 8 in Action by Raoul-Gabriel Urma, Mario Fusco, Alan Mycroft, 2015

https://blog.jetbrains.com/idea/2016/07/java-8-top-tips/

https://github.com/jOOQ/jOOL

Clean Code by Robert C. Martin

https://zeroturnaround.com/rebellabs/java-8-best-practices-cheat-sheet/

https://www.journeytomastery.net/2015/03/22/clean-code-and-java-8/

Curious about Java9: https://bentolor.github.io/java9-in-action/

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Enterprise Java Training

www.victorrentea.ro

victor.rentea@gmail.com

@victorrentea

Workshop: Searching Streams (30 min)

Workshop: Transforming Streams (40 min)

Workshop: Cleaning Lambdas (20 min)

Conclusions: Best Practices (20 min)

© Copyright Victor Rentea 2017

Victor Rentea

10 March 2017

Clean Lambdas & Streams in Java 8A Hands-on Experience