Enterprise Java Training
Victor Rentea
10 March 2017
Clean Lambdas & Streams in Java 8
A Hands-on Experience
Workshop: Searching Streams (30 min)
Workshop: Transforming Streams (40 min)
Workshop: Cleaning Lambdas (20 min)
Conclusions: Best Practices (20 min)
Agenda
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@victorrentea
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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;paymentMeth
od;status:Status;totalPrice:BigDecimal]-
orderLines*>[OrderLine|count:int;isSpecial
Offer]
[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 instance
instance method
instance
is known
𝒇(𝑶𝒓𝒅𝒆𝒓): 𝑫𝒂𝒕𝒆
𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕
𝒇(𝑶𝒓𝒅𝒆𝒓𝑴𝒂𝒑𝒑𝒆𝒓, 𝑶𝒓𝒅𝒆𝒓): 𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐
𝒇(): 𝑫𝒂𝒕𝒆
𝒇(): 𝒊𝒏𝒕
𝒇 𝑶𝒓𝒅𝒆𝒓 : 𝑶𝒓𝒅𝒆𝒓𝑫𝒕𝒐
𝒇(𝑺𝒕𝒓𝒊𝒏𝒈): 𝒊𝒏𝒕
𝒇(): 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 syntax
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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)
ARENEVERSEEN

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.filter(Order::isActive)
.map(Order::getCreationDate)
.findFirst()
orders.stream()
ARENEVERSEEN
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
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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)

VictorRentea.ro
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 8
A Hands-on Experience