SlideShare ist ein Scribd-Unternehmen logo
1 von 88
Downloaden Sie, um offline zu lesen
Java SE 8 Best Practices
A personal viewpoint
Stephen Colebourne, October 2015
Agenda
● ⇒ Introduction
● λ Lambdas
● f⒳ Functional interfaces
● ! Exceptions
● ? Optional
● ♒ Streams
● I Interfaces
● Date and Time
● Extras
Introduction
⇒
Introduction
● What is a Best Practice?
Introduction
● What is a Best Practice?
"commercial or professional procedures
that are accepted or prescribed as being
correct or most effective"
Introduction
● What is the Best Practice for Java SE 8?
Introduction
● What is the Best Practice for Java SE 8?
"whatever I say in the next 50 minutes"
Introduction
● Software Best Practice is mostly opinion
● Different conclusions perfectly possible
● My opinions are based on over a year using Java SE 8
Introduction
● Software Best Practice is mostly opinion
● Different conclusions perfectly possible
● My opinions are based on over a year using Java SE 8
But you must exercise your own judgement!
Java SE 8 version
● Use Java SE 8 update 40 or later
○ preferably use the latest available
● Earlier versions have annoying lambda/javac issues
Best
Practice
Lambdas
λ
Lambdas
● Block of code
○ like an anonymous inner class
● Always assigned to a Functional Interface
○ an interface with one abstract method
● Uses target typing
○ context determines type of the lambda
Lambdas - Example
// Java 7
List<Person> people = loadPeople();
Collections.sort(people, new Comparator<Person>() {
@Override
public int compare(Person p1, Person p2) {
return p1.name.compareTo(p2.name);
}
});
Lambdas - Example
// Java 7
List<Person> people = loadPeople();
Collections.sort(people, new Comparator<Person>() {
@Override
public int compare(Person p1, Person p2) {
return p1.name.compareTo(p2.name);
}
});
Lambdas - Example
// Java 8
List<Person> people = loadPeople();
Collections.sort(people,
(Person p1, Person p2)
p1.name.compareTo(p2.name)
);
Lambdas - Example
// Java 8
List<Person> people = loadPeople();
Collections.sort(people,
(Person p1, Person p2) -> p1.name.compareTo(p2.name));
Lambdas - Example
// Java 8
List<Person> people = loadPeople();
Collections.sort(people,
(Person p1, Person p2) -> p1.name.compareTo(p2.name));
Lambdas - Example
// Java 8
List<Person> people = loadPeople();
Collections.sort(people,
(p1, p2) -> p1.name.compareTo(p2.name));
Lambdas - Example
// Java 8
List<Person> people = loadPeople();
people.sort((p1, p2) -> p1.name.compareTo(p2.name));
Lambdas
● Make use of parameter type inference
● Only specify the types when compiler needs it
// prefer
(p1, p2) -> p1.name.compareTo(p2.name);
// avoid
(Person p1, Person p2) -> p1.name.compareTo(p2.name);
Best
Practice
Lambdas
● Do not use parameter brackets when optional
// prefer
str -> str.toUpperCase(Locale.US);
// avoid
(str) -> str.toUpperCase(Locale.US);
Best
Practice
Lambdas
● Do not declare local variables as 'final'
● Use new "effectively final" concept
public UnaryOperator<String> upperCaser(Locale locale) {
return str -> str.toUpperCase(locale);
}
Best
Practice
Do not declare as 'final'
Lambdas
● Prefer expression lambdas over block lambdas
● Use a separate method if necessary
// prefer
str -> str.toUpperCase(Locale.US);
// use with care
str -> {
return str.toUpperCase(Locale.US);
}
Best
Practice
Lambas for Abstraction
● Two large methods contain same code
● Except for one bit in the middle
● Can use a lambda to express the difference
Lambas for Abstraction
private int doFoo() {
// lots of code
// logic specific to method1
// lots of code
}
private int doBar() {
// lots of code
// logic specific to method2
// lots of code
}
Lambas for Abstraction
private int doFoo() {
return doFooBar( lambdaOfFooSpecificLogic );
}
private int doFooBar(Function<A, B> fn) {
// lots of code
result = fn.apply(arg)
// lots of code
}
Best
Practice
Example Abstraction
double[][] res = new double[rowCount][colCount];
for (int i = 0; i < rowCount; ++i) {
for (int j = 0; j < colCount; ++j) {
res[i][j] = pp.getCoefMatrix().get(i, j) * (nCoefs - j - 1);
}
}
DoubleMatrix2D coef = new DoubleMatrix2D(res);
Example Abstraction
DoubleMatrix2D coef = DoubleMatrix2D.of(
rowCount,
colCount,
(i, j) -> pp.getCoefMatrix().get(i, j) * (nCoefs - j - 1));
// new method
public static DoubleMatrix2D of(
int rows, int columns, IntIntToDoubleFunction valueFunction)
Functional interfaces
f⒳
Functional interfaces
● An interface with a single abstract method
○ Runnable
○ Comparable
○ Callable
● Java SE 8 adds many new functional interfaces
○ Function<T, R>
○ Predicate<T>
○ Supplier<T>
○ Consumer<T>
○ see java.util.function package
Functional interfaces
● Learn java.util.function package interface
● Only write your own if extra semantics are valuable
● If writing one, use @FunctionalInterface
@FunctionalInterface
public interface FooBarQuery {
public abstract Foo findAllFoos(Bar bar);
}
Best
Practice
Higher order methods
● Methods accepting lambdas are nothing special
○ declared type is just a normal interface
● However there are some subtleties
private String nameGreet(Supplier<String> nameSupplier) {
return "Hello " + nameSupplier.get();
}
// caller can use a lambda
String greeting = nameGreet(() -> "Bob");
Avoid method overloads
● Lambdas use target typing
● Clashes with method overloading
// avoid
public class Foo<T> {
public Foo<R> apply(Function<T, R> fn);
public Foo<T> apply(UnaryOperator<T> fn);
}
Avoid method overloads
● Lambdas use target typing
● Clashes with method overloading
● Use different method names to avoid clashes
Best
Practice
// prefer
public class Foo<T> {
public Foo<R> applyFunction(Function<T, R> fn);
public Foo<T> applyOperator(UnaryOperator<T> fn);
}
Functional interface last
● Prefer to have functional interface last
○ when method takes mixture of FI and non-FI
● Mostly stylistic
○ slightly better IDE error recovery
Best
Practice
// prefer
public Foo parse(Locale locale, Function<Locale,Foo> fn);
// avoid
public Foo parse(Function<Locale,Foo> fn, Locale locale);
Exceptions
!
Checked exceptions
● Most functional interfaces do not declare exceptions
● No simple way to put checked exceptions in lambdas
// does not compile!
public Function<String, Class> loader() {
return className -> Class.forName(className);
}
Throws a checked exception
Checked exceptions
● Write or find a helper method
● Converts checked exception to unchecked
public Function<String, Class> loader() {
return Unchecked.function(
className -> Class.forName(className));
}
Best
Practice
Checked exceptions
● Helper methods can deal with any block of code
○ convert to runtime exceptions
● May be a good case for a block lambda
Unchecked.wrap(() -> {
// any code that might throw a checked exception
});
Testing for exceptions
● Complete unit tests often need to test for exceptions
public void testConstructorRejectsEmptyString() {
try {
new FooBar("");
fail();
} catch (IllegalArgumentException ex) {
// expected
}
}
Testing for exceptions
● Use a helper method
● Lots of variations on this theme are possible
public void testConstructorRejectsEmptyString() {
TestHelper.assertThrows(
IllegalArgumentException.class, () -> new FooBar(""));
}
Best
Practice
Optional and null
?
https://www.flickr.com/photos/bigmacsc99/4003751542/
Boom!
Optional and null
● New class 'Optional' added to Java 8
● Polarizes opinions
○ functional programming dudes think it is the saviour of the universe
● Simple concept - two states
○ present, with a value - Optional.of(foo)
○ empty - Optional.empty()
Optional and null
● Standard code using null
// library, returns null if not found
public Foo findFoo(String key) { … }
// application code
Foo foo = findFoo(key);
if (foo == null) {
foo = Foo.DEFAULT; // or throw an exception
}
Optional and null
● Standard code using Optional
// library, returns null if not found
public Optional<Foo> findFoo(String key) { … }
// application code
Foo foo = findFoo(key).orElse(Foo.DEFAULT);
// or
Foo foo = findFoo(key).orElseThrow(RuntimeException::new);
Optional and null
● Variable of type Optional must never be null
● Never ever
● Never, never, never, never!
Best
Practice
Optional
● Prefer "functional" methods like 'orElse()'
● using 'isPresent()' a lot is misusing the feature
Best
Practice
// prefer
Foo foo = findFoo(key).orElse(Foo.DEFAULT);
// avoid
Optional<Foo> optFoo = findFoo(key);
if (optFoo.isPresent()) { … }
Optional
● Have a discussion and choose an approach
A. Use everywhere
B. Use instead of null on public APIs, input and output
C. Use instead of null on public return types
D. Use in a few selected places
E. Do not use
Best
Practice
Optional
● Have a discussion and choose an approach
A. Use everywhere
B. Use instead of null on public APIs, input and output
C. Use instead of null on public return types
↖ my preferred choice ↗
D. Use in a few selected places
E. Do not use
Best
Practice
Optional
● Optional is a class
● Some memory/performance cost to using it
● Not serializable
● Not ideal to be an instance variable
● JDK authors added it for return types
● Use in parameters often annoying for callers
● Use as return type gets best value from concept
http://blog.joda.org/2015/08/java-se-8-optional-pragmatic-approach.html
Streams
♒
Streams
● Most loops are the same
● Repetitive design patterns
● Stream library provides an abstraction
● Lambdas used to pass the interesting bits
Streams
List<Trade> trades = loadTrades();
List<Money> valued = new ArrayList<Money>();
for (Trade t : trades) {
if (t.isActive()) {
Money pv = presentValue(t);
valued.add(pv);
}
}
Loop to build output
list from input
Only interested in
some trades
Converts each trade
to the money value
Streams
List<Trade> trades = loadTrades();
List<Money> valued = new ArrayList<Money>();
for (Trade t : trades) {
if (t.isActive()) {
Money pv = presentValue(t);
valued.add(pv);
}
}
Streams
List<Trade> trades = loadTrades();
List<Money> valued = new ArrayList<Money>();
for (Trade t : trades) {
if (t.isActive()) {
Money pv = presentValue(t);
valued.add(pv);
}
}
Streams
List<Trade> trades = loadTrades();
List<Money> valued = List
trades
t.isActive()
presentValue(t)
Streams
List<Trade> trades = loadTrades();
List<Money> valued = // List
// trades
// t.isActive()
// presentValue(t)
Streams
List<Trade> trades = loadTrades();
List<Money> valued = // List
trades.stream() // trades
// t.isActive()
// presentValue(t)
Streams
List<Trade> trades = loadTrades();
List<Money> valued = // List
trades.stream() // trades
.filter(t -> t.isActive()) // t.isActive()
// presentValue(t)
Streams
List<Trade> trades = loadTrades();
List<Money> valued = // List
trades.stream() // trades
.filter(t -> t.isActive()) // t.isActive()
.map(t -> presentValue(t)) // presentValue(t)
Streams
List<Trade> trades = loadTrades();
List<Money> valued = // List
trades.stream() // trades
.filter(t -> t.isActive()) // t.isActive()
.map(t -> presentValue(t)) // presentValue(t)
.collect(Collectors.toList());
Streams
List<Trade> trades = loadTrades();
List<Money> valued =
trades.stream()
.filter(t -> t.isActive())
.map(t -> presentValue(t))
.collect(Collectors.toList());
Streams
● Streams are great, sometimes
● Important not to get carried away
● Design focus was on Collections, not Maps
● Key goal was simple parallelism
Streams
List<Trade> trades = loadTrades();
List<Money> valued =
trades.stream()
.filter(t -> t.isActive())
.map(t -> presentValue(t))
.collect(Collectors.toList());
Streams
List<Trade> trades = loadTrades();
List<Money> valued =
trades.parallelStream()
.filter(t -> t.isActive())
.map(t -> presentValue(t))
.collect(Collectors.toList());
Streams
● Do not overdo it
● Stream not always more readable than loop
● Good for Collections, less so for Maps
● Don't obsess about method references
○ IntelliJ hint may not be the best idea
Best
Practice
Streams
● Benchmark use in performance critical sections
● Parallel streams must be used with great care
● Shared execution pool can be deceiving
Best
Practice
Streams
List<Trade> trades = loadTrades();
Predicate<Trade> activePredicate = t -> t.isActive();
Function<Trade, Money> valueFn = t -> presentValue(t);
List<Money> valued =
trades.stream()
.filter(activePredicate)
.map(valueFn)
.collect(Collectors.toList());
Top
Tip
● Extract lines if struggling to get to compile
Streams
List<Trade> trades = loadTrades();
List<Money> valued =
trades.stream()
.filter(t.isActive())
.map((Trade t) -> presentValue(t))
.collect(Collectors.toList());
● Sometimes compiler needs a type hint
Top
Tip
Streams
● Learn to love 'Collector' interface
● Complex, but useful
● Sometime necessary to write them
● Need collectors for Guava 'ImmutableList' and friends
○ see 'Guavate' class in OpenGamma Strata
Interfaces
I
Interfaces
● Now have super-powers
● Default methods
○ normal method, but on an interface
● Static methods
○ normal static method, but on an interface
● Extend interfaces without breaking compatibility
● Cannot default equals/hashCode/toString
Interfaces
● New macro-design options
● Instead of factory class, use static method on interface
● Instead of abstract class, use interface with defaults
● Result tends to be fewer classes and better API
Top
Tip
Interfaces
● If factory method is static on interface
● And all API methods are on interface
● Can implementation class be package scoped?
Best
Practice
Coding Style
● Use modifiers in interfaces
● Much clearer now there are different types of method
● Prepares for possible future with non-public methods
Best
Practice
public interface Foo {
public static of(String key) { … }
public abstract getKey();
public default isActive() { … }
}
Date and Time
Date and Time
● New Date and Time API - JSR 310
● Covers dates, times, instants, periods, durations
● Brings 80%+ of Joda-Time to the JDK
● Fixes the mistakes in Joda-Time
Date and Time
Class Date Time ZoneOffset ZoneId Example
LocalDate ✔ ❌ ❌ ❌ 2015-12-03
LocalTime ❌ ✔ ❌ ❌ 11:30
LocalDateTime ✔ ✔ ❌ ❌ 2015-12-03T11:30
OffsetDateTime ✔ ✔ ✔ ❌ 2015-12-03T11:30+01:00
ZonedDateTime ✔ ✔ ✔ ✔ 2015-12-03T11:30+01:00
[Europe/London]
Instant ❌ ❌ ❌ ❌ 123456789 nanos from
1970-01-01T00:00Z
Date and Time
● Move away from Joda-Time
● Avoid java.util.Date and java.util.Calendar
● Use ThreeTen-Extra project if necessary
○ http://www.threeten.org/threeten-extra/
● Focus on four most useful types
○ LocalDate, LocalTime, ZonedDateTime, Instant
● Network formats like XML/JSON use offset types
○ OffsetTime, OffsetDateTime
Best
Practice
Date and Time
● Temporal interfaces are low-level
● Use concrete types
Best
Practice
// prefer
LocalDate date = LocalDate.of(2015, 10, 15);
// avoid
Temporal date = LocalDate.of(2015, 10, 15);
Rocket powered
Other features
● Base64
● Arithmetic without numeric overflow
● Unsigned arithmetic
● StampedLock
● CompletableFuture
● LongAdder/LongAccumulator
● Enhanced control of OS processes
Other Features
● Enhanced annotations
● Reflection on method parameters
● No PermGen in Hotspot JVM
● Nashorn JavaScript
● JavaFX is finally ready to replace Swing
Try a Java 8 open source library
● JOOL
○ https://github.com/jOOQ/jOOL
● ThrowingLambdas
○ https://github.com/fge/throwing-lambdas
● Parts of OpenGamma Strata (strata-collect - Guavate)
○ https://github.com/OpenGamma/Strata
● But beware excessively functional ones
○ most push ideas that don't really work well in Java
Immutability
● Favour immutable classes
● Lambdas and streams prefer this
● Preparation for value types (Java 10?)
● Use Joda-Beans to generate immutable "beans"
○ http://www.joda.org/joda-beans/
Summary
J8
Summary
● Java 8 is great
● Can be quite different to Java 7 and earlier
● Vital to rethink coding style and standards
○ methods on interfaces make a big difference
● Beware the functional programming/Scala dudes
○ a lot of their advice is simply not appropriate for Java

Más contenido relacionado

Was ist angesagt?

Introduction to Spring's Dependency Injection
Introduction to Spring's Dependency InjectionIntroduction to Spring's Dependency Injection
Introduction to Spring's Dependency InjectionRichard Paul
 
Docker 101: Introduction to Docker
Docker 101: Introduction to DockerDocker 101: Introduction to Docker
Docker 101: Introduction to DockerDocker, Inc.
 
Query and audit logging in cassandra
Query and audit logging in cassandraQuery and audit logging in cassandra
Query and audit logging in cassandraVinay Kumar Chella
 
Spring Framework - Data Access
Spring Framework - Data AccessSpring Framework - Data Access
Spring Framework - Data AccessDzmitry Naskou
 
CKA Certified Kubernetes Administrator Notes
CKA Certified Kubernetes Administrator Notes CKA Certified Kubernetes Administrator Notes
CKA Certified Kubernetes Administrator Notes Adnan Rashid
 
Introduction to Docker Compose
Introduction to Docker ComposeIntroduction to Docker Compose
Introduction to Docker ComposeAjeet Singh Raina
 
Introduction to Testcontainers
Introduction to TestcontainersIntroduction to Testcontainers
Introduction to TestcontainersVMware Tanzu
 
Introduction to kubernetes
Introduction to kubernetesIntroduction to kubernetes
Introduction to kubernetesGabriel Carro
 
Spring Boot Observability
Spring Boot ObservabilitySpring Boot Observability
Spring Boot ObservabilityVMware Tanzu
 
Spring boot introduction
Spring boot introductionSpring boot introduction
Spring boot introductionRasheed Waraich
 
Docker Container Security
Docker Container SecurityDocker Container Security
Docker Container SecuritySuraj Khetani
 
Docker로 서버 개발 편하게 하기
Docker로 서버 개발 편하게 하기Docker로 서버 개발 편하게 하기
Docker로 서버 개발 편하게 하기Dronix
 
Real Life Clean Architecture
Real Life Clean ArchitectureReal Life Clean Architecture
Real Life Clean ArchitectureMattia Battiston
 
Performance of Microservice frameworks on different JVMs
Performance of Microservice frameworks on different JVMsPerformance of Microservice frameworks on different JVMs
Performance of Microservice frameworks on different JVMsMaarten Smeets
 
Building large scale, job processing systems with Scala Akka Actor framework
Building large scale, job processing systems with Scala Akka Actor frameworkBuilding large scale, job processing systems with Scala Akka Actor framework
Building large scale, job processing systems with Scala Akka Actor frameworkVignesh Sukumar
 
Kubernetes and container security
Kubernetes and container securityKubernetes and container security
Kubernetes and container securityVolodymyr Shynkar
 
Monitoring, Logging and Tracing on Kubernetes
Monitoring, Logging and Tracing on KubernetesMonitoring, Logging and Tracing on Kubernetes
Monitoring, Logging and Tracing on KubernetesMartin Etmajer
 

Was ist angesagt? (20)

Typescript ppt
Typescript pptTypescript ppt
Typescript ppt
 
Introduction to Spring's Dependency Injection
Introduction to Spring's Dependency InjectionIntroduction to Spring's Dependency Injection
Introduction to Spring's Dependency Injection
 
Terraform
TerraformTerraform
Terraform
 
Docker 101: Introduction to Docker
Docker 101: Introduction to DockerDocker 101: Introduction to Docker
Docker 101: Introduction to Docker
 
Query and audit logging in cassandra
Query and audit logging in cassandraQuery and audit logging in cassandra
Query and audit logging in cassandra
 
Spring Framework - Data Access
Spring Framework - Data AccessSpring Framework - Data Access
Spring Framework - Data Access
 
CKA Certified Kubernetes Administrator Notes
CKA Certified Kubernetes Administrator Notes CKA Certified Kubernetes Administrator Notes
CKA Certified Kubernetes Administrator Notes
 
Spring Boot
Spring BootSpring Boot
Spring Boot
 
Introduction to Docker Compose
Introduction to Docker ComposeIntroduction to Docker Compose
Introduction to Docker Compose
 
Introduction to Testcontainers
Introduction to TestcontainersIntroduction to Testcontainers
Introduction to Testcontainers
 
Introduction to kubernetes
Introduction to kubernetesIntroduction to kubernetes
Introduction to kubernetes
 
Spring Boot Observability
Spring Boot ObservabilitySpring Boot Observability
Spring Boot Observability
 
Spring boot introduction
Spring boot introductionSpring boot introduction
Spring boot introduction
 
Docker Container Security
Docker Container SecurityDocker Container Security
Docker Container Security
 
Docker로 서버 개발 편하게 하기
Docker로 서버 개발 편하게 하기Docker로 서버 개발 편하게 하기
Docker로 서버 개발 편하게 하기
 
Real Life Clean Architecture
Real Life Clean ArchitectureReal Life Clean Architecture
Real Life Clean Architecture
 
Performance of Microservice frameworks on different JVMs
Performance of Microservice frameworks on different JVMsPerformance of Microservice frameworks on different JVMs
Performance of Microservice frameworks on different JVMs
 
Building large scale, job processing systems with Scala Akka Actor framework
Building large scale, job processing systems with Scala Akka Actor frameworkBuilding large scale, job processing systems with Scala Akka Actor framework
Building large scale, job processing systems with Scala Akka Actor framework
 
Kubernetes and container security
Kubernetes and container securityKubernetes and container security
Kubernetes and container security
 
Monitoring, Logging and Tracing on Kubernetes
Monitoring, Logging and Tracing on KubernetesMonitoring, Logging and Tracing on Kubernetes
Monitoring, Logging and Tracing on Kubernetes
 

Andere mochten auch

Advanced Production Debugging
Advanced Production DebuggingAdvanced Production Debugging
Advanced Production DebuggingTakipi
 
Java 9: The (G1) GC Awakens!
Java 9: The (G1) GC Awakens!Java 9: The (G1) GC Awakens!
Java 9: The (G1) GC Awakens!Monica Beckwith
 
10 SQL Tricks that You Didn't Think Were Possible
10 SQL Tricks that You Didn't Think Were Possible10 SQL Tricks that You Didn't Think Were Possible
10 SQL Tricks that You Didn't Think Were PossibleLukas Eder
 
Project Jigsaw in JDK 9: Modularity Comes To Java
Project Jigsaw in JDK 9: Modularity Comes To JavaProject Jigsaw in JDK 9: Modularity Comes To Java
Project Jigsaw in JDK 9: Modularity Comes To JavaC4Media
 
Microservices + Oracle: A Bright Future
Microservices + Oracle: A Bright FutureMicroservices + Oracle: A Bright Future
Microservices + Oracle: A Bright FutureKelly Goetsch
 
More Little Wonders of C#/.NET
More Little Wonders of C#/.NETMore Little Wonders of C#/.NET
More Little Wonders of C#/.NETBlackRabbitCoder
 
Alphorm.com support de la formation programmer en C# 6
Alphorm.com support de la formation programmer en C# 6Alphorm.com support de la formation programmer en C# 6
Alphorm.com support de la formation programmer en C# 6Alphorm
 

Andere mochten auch (15)

Advanced Production Debugging
Advanced Production DebuggingAdvanced Production Debugging
Advanced Production Debugging
 
In Search of Segmentation
In Search of SegmentationIn Search of Segmentation
In Search of Segmentation
 
Java 9: The (G1) GC Awakens!
Java 9: The (G1) GC Awakens!Java 9: The (G1) GC Awakens!
Java 9: The (G1) GC Awakens!
 
10 SQL Tricks that You Didn't Think Were Possible
10 SQL Tricks that You Didn't Think Were Possible10 SQL Tricks that You Didn't Think Were Possible
10 SQL Tricks that You Didn't Think Were Possible
 
Project Jigsaw in JDK 9: Modularity Comes To Java
Project Jigsaw in JDK 9: Modularity Comes To JavaProject Jigsaw in JDK 9: Modularity Comes To Java
Project Jigsaw in JDK 9: Modularity Comes To Java
 
Scala Days NYC 2016
Scala Days NYC 2016Scala Days NYC 2016
Scala Days NYC 2016
 
Microservices + Oracle: A Bright Future
Microservices + Oracle: A Bright FutureMicroservices + Oracle: A Bright Future
Microservices + Oracle: A Bright Future
 
C#/.NET Little Wonders
C#/.NET Little WondersC#/.NET Little Wonders
C#/.NET Little Wonders
 
More Little Wonders of C#/.NET
More Little Wonders of C#/.NETMore Little Wonders of C#/.NET
More Little Wonders of C#/.NET
 
Programming in c#
Programming in c#Programming in c#
Programming in c#
 
Java Notes
Java NotesJava Notes
Java Notes
 
Core java complete notes - Contact at +91-814-614-5674
Core java complete notes - Contact at +91-814-614-5674Core java complete notes - Contact at +91-814-614-5674
Core java complete notes - Contact at +91-814-614-5674
 
Core java slides
Core java slidesCore java slides
Core java slides
 
Introduction to java
Introduction to javaIntroduction to java
Introduction to java
 
Alphorm.com support de la formation programmer en C# 6
Alphorm.com support de la formation programmer en C# 6Alphorm.com support de la formation programmer en C# 6
Alphorm.com support de la formation programmer en C# 6
 

Ähnlich wie Java SE 8 best practices

java150929145120-lva1-app6892 (2).pptx
java150929145120-lva1-app6892 (2).pptxjava150929145120-lva1-app6892 (2).pptx
java150929145120-lva1-app6892 (2).pptxBruceLee275640
 
Advanced PHP Simplified - Sunshine PHP 2018
Advanced PHP Simplified - Sunshine PHP 2018Advanced PHP Simplified - Sunshine PHP 2018
Advanced PHP Simplified - Sunshine PHP 2018Mark Niebergall
 
Java 8 presentation
Java 8 presentationJava 8 presentation
Java 8 presentationVan Huong
 
Android Open source coading guidel ine
Android Open source coading guidel ineAndroid Open source coading guidel ine
Android Open source coading guidel inePragati Singh
 
Back-2-Basics: .NET Coding Standards For The Real World (2011)
Back-2-Basics: .NET Coding Standards For The Real World (2011)Back-2-Basics: .NET Coding Standards For The Real World (2011)
Back-2-Basics: .NET Coding Standards For The Real World (2011)David McCarter
 
Lambda Chops - Recipes for Simpler, More Expressive Code
Lambda Chops - Recipes for Simpler, More Expressive CodeLambda Chops - Recipes for Simpler, More Expressive Code
Lambda Chops - Recipes for Simpler, More Expressive CodeIan Robertson
 
Functional programming in java 8 by harmeet singh
Functional programming in java 8 by harmeet singhFunctional programming in java 8 by harmeet singh
Functional programming in java 8 by harmeet singhHarmeet Singh(Taara)
 
Learn To Code: Introduction to java
Learn To Code: Introduction to javaLearn To Code: Introduction to java
Learn To Code: Introduction to javaSadhanaParameswaran
 
Apache Dispatch
Apache DispatchApache Dispatch
Apache DispatchFred Moyer
 
Method Handles in Java
Method Handles in JavaMethod Handles in Java
Method Handles in Javahendersk
 
Intro to java 8
Intro to java 8Intro to java 8
Intro to java 8John Godoi
 
Java Presentation For Syntax
Java Presentation For SyntaxJava Presentation For Syntax
Java Presentation For SyntaxPravinYalameli
 
Object oriented programming in java
Object oriented programming in javaObject oriented programming in java
Object oriented programming in javaElizabeth alexander
 
TWINS: OOP and FP - Warburton
TWINS: OOP and FP - WarburtonTWINS: OOP and FP - Warburton
TWINS: OOP and FP - WarburtonCodemotion
 

Ähnlich wie Java SE 8 best practices (20)

java150929145120-lva1-app6892 (2).pptx
java150929145120-lva1-app6892 (2).pptxjava150929145120-lva1-app6892 (2).pptx
java150929145120-lva1-app6892 (2).pptx
 
Advanced PHP Simplified - Sunshine PHP 2018
Advanced PHP Simplified - Sunshine PHP 2018Advanced PHP Simplified - Sunshine PHP 2018
Advanced PHP Simplified - Sunshine PHP 2018
 
Java 8 presentation
Java 8 presentationJava 8 presentation
Java 8 presentation
 
Java For Automation
Java   For AutomationJava   For Automation
Java For Automation
 
Advanced PHP Simplified
Advanced PHP SimplifiedAdvanced PHP Simplified
Advanced PHP Simplified
 
Android Open source coading guidel ine
Android Open source coading guidel ineAndroid Open source coading guidel ine
Android Open source coading guidel ine
 
Back-2-Basics: .NET Coding Standards For The Real World (2011)
Back-2-Basics: .NET Coding Standards For The Real World (2011)Back-2-Basics: .NET Coding Standards For The Real World (2011)
Back-2-Basics: .NET Coding Standards For The Real World (2011)
 
Core java
Core javaCore java
Core java
 
Lambda Chops - Recipes for Simpler, More Expressive Code
Lambda Chops - Recipes for Simpler, More Expressive CodeLambda Chops - Recipes for Simpler, More Expressive Code
Lambda Chops - Recipes for Simpler, More Expressive Code
 
Java conventions
Java conventionsJava conventions
Java conventions
 
Java 7 & 8 New Features
Java 7 & 8 New FeaturesJava 7 & 8 New Features
Java 7 & 8 New Features
 
Functional programming in java 8 by harmeet singh
Functional programming in java 8 by harmeet singhFunctional programming in java 8 by harmeet singh
Functional programming in java 8 by harmeet singh
 
Learn To Code: Introduction to java
Learn To Code: Introduction to javaLearn To Code: Introduction to java
Learn To Code: Introduction to java
 
Apache Dispatch
Apache DispatchApache Dispatch
Apache Dispatch
 
Method Handles in Java
Method Handles in JavaMethod Handles in Java
Method Handles in Java
 
Intro to java 8
Intro to java 8Intro to java 8
Intro to java 8
 
Lambdas in Java 8
Lambdas in Java 8Lambdas in Java 8
Lambdas in Java 8
 
Java Presentation For Syntax
Java Presentation For SyntaxJava Presentation For Syntax
Java Presentation For Syntax
 
Object oriented programming in java
Object oriented programming in javaObject oriented programming in java
Object oriented programming in java
 
TWINS: OOP and FP - Warburton
TWINS: OOP and FP - WarburtonTWINS: OOP and FP - Warburton
TWINS: OOP and FP - Warburton
 

Mehr von Stephen Colebourne

Java SE 9 modules - an introduction (July 2018)
Java SE 9 modules - an introduction (July 2018)Java SE 9 modules - an introduction (July 2018)
Java SE 9 modules - an introduction (July 2018)Stephen Colebourne
 
Amber and beyond: Java language changes
Amber and beyond: Java language changesAmber and beyond: Java language changes
Amber and beyond: Java language changesStephen Colebourne
 
Java SE 9 modules (JPMS) - an introduction
Java SE 9 modules (JPMS) - an introductionJava SE 9 modules (JPMS) - an introduction
Java SE 9 modules (JPMS) - an introductionStephen Colebourne
 
Strata, Open Source Market Risk
Strata, Open Source Market RiskStrata, Open Source Market Risk
Strata, Open Source Market RiskStephen Colebourne
 

Mehr von Stephen Colebourne (6)

Java SE 9 modules - an introduction (July 2018)
Java SE 9 modules - an introduction (July 2018)Java SE 9 modules - an introduction (July 2018)
Java SE 9 modules - an introduction (July 2018)
 
Amber and beyond: Java language changes
Amber and beyond: Java language changesAmber and beyond: Java language changes
Amber and beyond: Java language changes
 
Java SE 9 modules (JPMS) - an introduction
Java SE 9 modules (JPMS) - an introductionJava SE 9 modules (JPMS) - an introduction
Java SE 9 modules (JPMS) - an introduction
 
Strata, Open Source Market Risk
Strata, Open Source Market RiskStrata, Open Source Market Risk
Strata, Open Source Market Risk
 
Java SE 8 library design
Java SE 8 library designJava SE 8 library design
Java SE 8 library design
 
Code generating beans in Java
Code generating beans in JavaCode generating beans in Java
Code generating beans in Java
 

Último

Boost Efficiency: Sabre API Integration Made Easy
Boost Efficiency: Sabre API Integration Made EasyBoost Efficiency: Sabre API Integration Made Easy
Boost Efficiency: Sabre API Integration Made Easymichealwillson701
 
Technical improvements. Reasons. Methods. Estimations. CJ
Technical improvements.  Reasons. Methods. Estimations. CJTechnical improvements.  Reasons. Methods. Estimations. CJ
Technical improvements. Reasons. Methods. Estimations. CJpolinaucc
 
Unlocking AI: Navigating Open Source vs. Commercial Frontiers
Unlocking AI:Navigating Open Source vs. Commercial FrontiersUnlocking AI:Navigating Open Source vs. Commercial Frontiers
Unlocking AI: Navigating Open Source vs. Commercial FrontiersRaphaël Semeteys
 
Practical Advice for FDA’s 510(k) Requirements.pdf
Practical Advice for FDA’s 510(k) Requirements.pdfPractical Advice for FDA’s 510(k) Requirements.pdf
Practical Advice for FDA’s 510(k) Requirements.pdfICS
 
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...jackiepotts6
 
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...Splashtop Inc
 
Enterprise Content Managements Solutions
Enterprise Content Managements SolutionsEnterprise Content Managements Solutions
Enterprise Content Managements SolutionsIQBG inc
 
Leveling Up your Branding and Mastering MERN: Fullstack WebDev
Leveling Up your Branding and Mastering MERN: Fullstack WebDevLeveling Up your Branding and Mastering MERN: Fullstack WebDev
Leveling Up your Branding and Mastering MERN: Fullstack WebDevpmgdscunsri
 
BATbern52 Swisscom's Journey into Data Mesh
BATbern52 Swisscom's Journey into Data MeshBATbern52 Swisscom's Journey into Data Mesh
BATbern52 Swisscom's Journey into Data MeshBATbern
 
VuNet software organisation powerpoint deck
VuNet software organisation powerpoint deckVuNet software organisation powerpoint deck
VuNet software organisation powerpoint deckNaval Singh
 
Unlocking the Power of IoT: A comprehensive approach to real-time insights
Unlocking the Power of IoT: A comprehensive approach to real-time insightsUnlocking the Power of IoT: A comprehensive approach to real-time insights
Unlocking the Power of IoT: A comprehensive approach to real-time insightsconfluent
 
Revolutionize Your Field Service Management with FSM Grid
Revolutionize Your Field Service Management with FSM GridRevolutionize Your Field Service Management with FSM Grid
Revolutionize Your Field Service Management with FSM GridMathew Thomas
 
BusinessGPT - SECURITY AND GOVERNANCE FOR GENERATIVE AI.pptx
BusinessGPT  - SECURITY AND GOVERNANCE  FOR GENERATIVE AI.pptxBusinessGPT  - SECURITY AND GOVERNANCE  FOR GENERATIVE AI.pptx
BusinessGPT - SECURITY AND GOVERNANCE FOR GENERATIVE AI.pptxAGATSoftware
 
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...Maxim Salnikov
 
Einstein Copilot Conversational AI for your CRM.pdf
Einstein Copilot Conversational AI for your CRM.pdfEinstein Copilot Conversational AI for your CRM.pdf
Einstein Copilot Conversational AI for your CRM.pdfCloudMetic
 
Steps to Successfully Hire Ionic Developers
Steps to Successfully Hire Ionic DevelopersSteps to Successfully Hire Ionic Developers
Steps to Successfully Hire Ionic Developersmichealwillson701
 
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...telebusocialmarketin
 
User Experience Designer | Kaylee Miller Resume
User Experience Designer | Kaylee Miller ResumeUser Experience Designer | Kaylee Miller Resume
User Experience Designer | Kaylee Miller ResumeKaylee Miller
 
MUT4SLX: Extensions for Mutation Testing of Stateflow Models
MUT4SLX: Extensions for Mutation Testing of Stateflow ModelsMUT4SLX: Extensions for Mutation Testing of Stateflow Models
MUT4SLX: Extensions for Mutation Testing of Stateflow ModelsUniversity of Antwerp
 

Último (20)

Boost Efficiency: Sabre API Integration Made Easy
Boost Efficiency: Sabre API Integration Made EasyBoost Efficiency: Sabre API Integration Made Easy
Boost Efficiency: Sabre API Integration Made Easy
 
Technical improvements. Reasons. Methods. Estimations. CJ
Technical improvements.  Reasons. Methods. Estimations. CJTechnical improvements.  Reasons. Methods. Estimations. CJ
Technical improvements. Reasons. Methods. Estimations. CJ
 
Unlocking AI: Navigating Open Source vs. Commercial Frontiers
Unlocking AI:Navigating Open Source vs. Commercial FrontiersUnlocking AI:Navigating Open Source vs. Commercial Frontiers
Unlocking AI: Navigating Open Source vs. Commercial Frontiers
 
Practical Advice for FDA’s 510(k) Requirements.pdf
Practical Advice for FDA’s 510(k) Requirements.pdfPractical Advice for FDA’s 510(k) Requirements.pdf
Practical Advice for FDA’s 510(k) Requirements.pdf
 
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...
03.2024_North America VMUG Optimizing RevOps using the power of ChatGPT in Ma...
 
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...
Splashtop Enterprise Brochure - Remote Computer Access and Remote Support Sof...
 
Enterprise Content Managements Solutions
Enterprise Content Managements SolutionsEnterprise Content Managements Solutions
Enterprise Content Managements Solutions
 
Leveling Up your Branding and Mastering MERN: Fullstack WebDev
Leveling Up your Branding and Mastering MERN: Fullstack WebDevLeveling Up your Branding and Mastering MERN: Fullstack WebDev
Leveling Up your Branding and Mastering MERN: Fullstack WebDev
 
BATbern52 Swisscom's Journey into Data Mesh
BATbern52 Swisscom's Journey into Data MeshBATbern52 Swisscom's Journey into Data Mesh
BATbern52 Swisscom's Journey into Data Mesh
 
VuNet software organisation powerpoint deck
VuNet software organisation powerpoint deckVuNet software organisation powerpoint deck
VuNet software organisation powerpoint deck
 
Unlocking the Power of IoT: A comprehensive approach to real-time insights
Unlocking the Power of IoT: A comprehensive approach to real-time insightsUnlocking the Power of IoT: A comprehensive approach to real-time insights
Unlocking the Power of IoT: A comprehensive approach to real-time insights
 
20140812 - OBD2 Solution
20140812 - OBD2 Solution20140812 - OBD2 Solution
20140812 - OBD2 Solution
 
Revolutionize Your Field Service Management with FSM Grid
Revolutionize Your Field Service Management with FSM GridRevolutionize Your Field Service Management with FSM Grid
Revolutionize Your Field Service Management with FSM Grid
 
BusinessGPT - SECURITY AND GOVERNANCE FOR GENERATIVE AI.pptx
BusinessGPT  - SECURITY AND GOVERNANCE  FOR GENERATIVE AI.pptxBusinessGPT  - SECURITY AND GOVERNANCE  FOR GENERATIVE AI.pptx
BusinessGPT - SECURITY AND GOVERNANCE FOR GENERATIVE AI.pptx
 
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...
If your code could speak, what would it tell you? Let GitHub Copilot Chat hel...
 
Einstein Copilot Conversational AI for your CRM.pdf
Einstein Copilot Conversational AI for your CRM.pdfEinstein Copilot Conversational AI for your CRM.pdf
Einstein Copilot Conversational AI for your CRM.pdf
 
Steps to Successfully Hire Ionic Developers
Steps to Successfully Hire Ionic DevelopersSteps to Successfully Hire Ionic Developers
Steps to Successfully Hire Ionic Developers
 
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...
Telebu Social -Whatsapp Business API : Mastering Omnichannel Business Communi...
 
User Experience Designer | Kaylee Miller Resume
User Experience Designer | Kaylee Miller ResumeUser Experience Designer | Kaylee Miller Resume
User Experience Designer | Kaylee Miller Resume
 
MUT4SLX: Extensions for Mutation Testing of Stateflow Models
MUT4SLX: Extensions for Mutation Testing of Stateflow ModelsMUT4SLX: Extensions for Mutation Testing of Stateflow Models
MUT4SLX: Extensions for Mutation Testing of Stateflow Models
 

Java SE 8 best practices

  • 1. Java SE 8 Best Practices A personal viewpoint Stephen Colebourne, October 2015
  • 2. Agenda ● ⇒ Introduction ● λ Lambdas ● f⒳ Functional interfaces ● ! Exceptions ● ? Optional ● ♒ Streams ● I Interfaces ● Date and Time ● Extras
  • 4. Introduction ● What is a Best Practice?
  • 5. Introduction ● What is a Best Practice? "commercial or professional procedures that are accepted or prescribed as being correct or most effective"
  • 6. Introduction ● What is the Best Practice for Java SE 8?
  • 7. Introduction ● What is the Best Practice for Java SE 8? "whatever I say in the next 50 minutes"
  • 8. Introduction ● Software Best Practice is mostly opinion ● Different conclusions perfectly possible ● My opinions are based on over a year using Java SE 8
  • 9. Introduction ● Software Best Practice is mostly opinion ● Different conclusions perfectly possible ● My opinions are based on over a year using Java SE 8 But you must exercise your own judgement!
  • 10. Java SE 8 version ● Use Java SE 8 update 40 or later ○ preferably use the latest available ● Earlier versions have annoying lambda/javac issues Best Practice
  • 12. Lambdas ● Block of code ○ like an anonymous inner class ● Always assigned to a Functional Interface ○ an interface with one abstract method ● Uses target typing ○ context determines type of the lambda
  • 13. Lambdas - Example // Java 7 List<Person> people = loadPeople(); Collections.sort(people, new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { return p1.name.compareTo(p2.name); } });
  • 14. Lambdas - Example // Java 7 List<Person> people = loadPeople(); Collections.sort(people, new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { return p1.name.compareTo(p2.name); } });
  • 15. Lambdas - Example // Java 8 List<Person> people = loadPeople(); Collections.sort(people, (Person p1, Person p2) p1.name.compareTo(p2.name) );
  • 16. Lambdas - Example // Java 8 List<Person> people = loadPeople(); Collections.sort(people, (Person p1, Person p2) -> p1.name.compareTo(p2.name));
  • 17. Lambdas - Example // Java 8 List<Person> people = loadPeople(); Collections.sort(people, (Person p1, Person p2) -> p1.name.compareTo(p2.name));
  • 18. Lambdas - Example // Java 8 List<Person> people = loadPeople(); Collections.sort(people, (p1, p2) -> p1.name.compareTo(p2.name));
  • 19. Lambdas - Example // Java 8 List<Person> people = loadPeople(); people.sort((p1, p2) -> p1.name.compareTo(p2.name));
  • 20. Lambdas ● Make use of parameter type inference ● Only specify the types when compiler needs it // prefer (p1, p2) -> p1.name.compareTo(p2.name); // avoid (Person p1, Person p2) -> p1.name.compareTo(p2.name); Best Practice
  • 21. Lambdas ● Do not use parameter brackets when optional // prefer str -> str.toUpperCase(Locale.US); // avoid (str) -> str.toUpperCase(Locale.US); Best Practice
  • 22. Lambdas ● Do not declare local variables as 'final' ● Use new "effectively final" concept public UnaryOperator<String> upperCaser(Locale locale) { return str -> str.toUpperCase(locale); } Best Practice Do not declare as 'final'
  • 23. Lambdas ● Prefer expression lambdas over block lambdas ● Use a separate method if necessary // prefer str -> str.toUpperCase(Locale.US); // use with care str -> { return str.toUpperCase(Locale.US); } Best Practice
  • 24. Lambas for Abstraction ● Two large methods contain same code ● Except for one bit in the middle ● Can use a lambda to express the difference
  • 25. Lambas for Abstraction private int doFoo() { // lots of code // logic specific to method1 // lots of code } private int doBar() { // lots of code // logic specific to method2 // lots of code }
  • 26. Lambas for Abstraction private int doFoo() { return doFooBar( lambdaOfFooSpecificLogic ); } private int doFooBar(Function<A, B> fn) { // lots of code result = fn.apply(arg) // lots of code } Best Practice
  • 27. Example Abstraction double[][] res = new double[rowCount][colCount]; for (int i = 0; i < rowCount; ++i) { for (int j = 0; j < colCount; ++j) { res[i][j] = pp.getCoefMatrix().get(i, j) * (nCoefs - j - 1); } } DoubleMatrix2D coef = new DoubleMatrix2D(res);
  • 28. Example Abstraction DoubleMatrix2D coef = DoubleMatrix2D.of( rowCount, colCount, (i, j) -> pp.getCoefMatrix().get(i, j) * (nCoefs - j - 1)); // new method public static DoubleMatrix2D of( int rows, int columns, IntIntToDoubleFunction valueFunction)
  • 30. Functional interfaces ● An interface with a single abstract method ○ Runnable ○ Comparable ○ Callable ● Java SE 8 adds many new functional interfaces ○ Function<T, R> ○ Predicate<T> ○ Supplier<T> ○ Consumer<T> ○ see java.util.function package
  • 31. Functional interfaces ● Learn java.util.function package interface ● Only write your own if extra semantics are valuable ● If writing one, use @FunctionalInterface @FunctionalInterface public interface FooBarQuery { public abstract Foo findAllFoos(Bar bar); } Best Practice
  • 32. Higher order methods ● Methods accepting lambdas are nothing special ○ declared type is just a normal interface ● However there are some subtleties private String nameGreet(Supplier<String> nameSupplier) { return "Hello " + nameSupplier.get(); } // caller can use a lambda String greeting = nameGreet(() -> "Bob");
  • 33. Avoid method overloads ● Lambdas use target typing ● Clashes with method overloading // avoid public class Foo<T> { public Foo<R> apply(Function<T, R> fn); public Foo<T> apply(UnaryOperator<T> fn); }
  • 34. Avoid method overloads ● Lambdas use target typing ● Clashes with method overloading ● Use different method names to avoid clashes Best Practice // prefer public class Foo<T> { public Foo<R> applyFunction(Function<T, R> fn); public Foo<T> applyOperator(UnaryOperator<T> fn); }
  • 35. Functional interface last ● Prefer to have functional interface last ○ when method takes mixture of FI and non-FI ● Mostly stylistic ○ slightly better IDE error recovery Best Practice // prefer public Foo parse(Locale locale, Function<Locale,Foo> fn); // avoid public Foo parse(Function<Locale,Foo> fn, Locale locale);
  • 37. Checked exceptions ● Most functional interfaces do not declare exceptions ● No simple way to put checked exceptions in lambdas // does not compile! public Function<String, Class> loader() { return className -> Class.forName(className); } Throws a checked exception
  • 38. Checked exceptions ● Write or find a helper method ● Converts checked exception to unchecked public Function<String, Class> loader() { return Unchecked.function( className -> Class.forName(className)); } Best Practice
  • 39. Checked exceptions ● Helper methods can deal with any block of code ○ convert to runtime exceptions ● May be a good case for a block lambda Unchecked.wrap(() -> { // any code that might throw a checked exception });
  • 40. Testing for exceptions ● Complete unit tests often need to test for exceptions public void testConstructorRejectsEmptyString() { try { new FooBar(""); fail(); } catch (IllegalArgumentException ex) { // expected } }
  • 41. Testing for exceptions ● Use a helper method ● Lots of variations on this theme are possible public void testConstructorRejectsEmptyString() { TestHelper.assertThrows( IllegalArgumentException.class, () -> new FooBar("")); } Best Practice
  • 44. Optional and null ● New class 'Optional' added to Java 8 ● Polarizes opinions ○ functional programming dudes think it is the saviour of the universe ● Simple concept - two states ○ present, with a value - Optional.of(foo) ○ empty - Optional.empty()
  • 45. Optional and null ● Standard code using null // library, returns null if not found public Foo findFoo(String key) { … } // application code Foo foo = findFoo(key); if (foo == null) { foo = Foo.DEFAULT; // or throw an exception }
  • 46. Optional and null ● Standard code using Optional // library, returns null if not found public Optional<Foo> findFoo(String key) { … } // application code Foo foo = findFoo(key).orElse(Foo.DEFAULT); // or Foo foo = findFoo(key).orElseThrow(RuntimeException::new);
  • 47. Optional and null ● Variable of type Optional must never be null ● Never ever ● Never, never, never, never! Best Practice
  • 48. Optional ● Prefer "functional" methods like 'orElse()' ● using 'isPresent()' a lot is misusing the feature Best Practice // prefer Foo foo = findFoo(key).orElse(Foo.DEFAULT); // avoid Optional<Foo> optFoo = findFoo(key); if (optFoo.isPresent()) { … }
  • 49. Optional ● Have a discussion and choose an approach A. Use everywhere B. Use instead of null on public APIs, input and output C. Use instead of null on public return types D. Use in a few selected places E. Do not use Best Practice
  • 50. Optional ● Have a discussion and choose an approach A. Use everywhere B. Use instead of null on public APIs, input and output C. Use instead of null on public return types ↖ my preferred choice ↗ D. Use in a few selected places E. Do not use Best Practice
  • 51. Optional ● Optional is a class ● Some memory/performance cost to using it ● Not serializable ● Not ideal to be an instance variable ● JDK authors added it for return types ● Use in parameters often annoying for callers ● Use as return type gets best value from concept http://blog.joda.org/2015/08/java-se-8-optional-pragmatic-approach.html
  • 53. Streams ● Most loops are the same ● Repetitive design patterns ● Stream library provides an abstraction ● Lambdas used to pass the interesting bits
  • 54. Streams List<Trade> trades = loadTrades(); List<Money> valued = new ArrayList<Money>(); for (Trade t : trades) { if (t.isActive()) { Money pv = presentValue(t); valued.add(pv); } } Loop to build output list from input Only interested in some trades Converts each trade to the money value
  • 55. Streams List<Trade> trades = loadTrades(); List<Money> valued = new ArrayList<Money>(); for (Trade t : trades) { if (t.isActive()) { Money pv = presentValue(t); valued.add(pv); } }
  • 56. Streams List<Trade> trades = loadTrades(); List<Money> valued = new ArrayList<Money>(); for (Trade t : trades) { if (t.isActive()) { Money pv = presentValue(t); valued.add(pv); } }
  • 57. Streams List<Trade> trades = loadTrades(); List<Money> valued = List trades t.isActive() presentValue(t)
  • 58. Streams List<Trade> trades = loadTrades(); List<Money> valued = // List // trades // t.isActive() // presentValue(t)
  • 59. Streams List<Trade> trades = loadTrades(); List<Money> valued = // List trades.stream() // trades // t.isActive() // presentValue(t)
  • 60. Streams List<Trade> trades = loadTrades(); List<Money> valued = // List trades.stream() // trades .filter(t -> t.isActive()) // t.isActive() // presentValue(t)
  • 61. Streams List<Trade> trades = loadTrades(); List<Money> valued = // List trades.stream() // trades .filter(t -> t.isActive()) // t.isActive() .map(t -> presentValue(t)) // presentValue(t)
  • 62. Streams List<Trade> trades = loadTrades(); List<Money> valued = // List trades.stream() // trades .filter(t -> t.isActive()) // t.isActive() .map(t -> presentValue(t)) // presentValue(t) .collect(Collectors.toList());
  • 63. Streams List<Trade> trades = loadTrades(); List<Money> valued = trades.stream() .filter(t -> t.isActive()) .map(t -> presentValue(t)) .collect(Collectors.toList());
  • 64. Streams ● Streams are great, sometimes ● Important not to get carried away ● Design focus was on Collections, not Maps ● Key goal was simple parallelism
  • 65. Streams List<Trade> trades = loadTrades(); List<Money> valued = trades.stream() .filter(t -> t.isActive()) .map(t -> presentValue(t)) .collect(Collectors.toList());
  • 66. Streams List<Trade> trades = loadTrades(); List<Money> valued = trades.parallelStream() .filter(t -> t.isActive()) .map(t -> presentValue(t)) .collect(Collectors.toList());
  • 67. Streams ● Do not overdo it ● Stream not always more readable than loop ● Good for Collections, less so for Maps ● Don't obsess about method references ○ IntelliJ hint may not be the best idea Best Practice
  • 68. Streams ● Benchmark use in performance critical sections ● Parallel streams must be used with great care ● Shared execution pool can be deceiving Best Practice
  • 69. Streams List<Trade> trades = loadTrades(); Predicate<Trade> activePredicate = t -> t.isActive(); Function<Trade, Money> valueFn = t -> presentValue(t); List<Money> valued = trades.stream() .filter(activePredicate) .map(valueFn) .collect(Collectors.toList()); Top Tip ● Extract lines if struggling to get to compile
  • 70. Streams List<Trade> trades = loadTrades(); List<Money> valued = trades.stream() .filter(t.isActive()) .map((Trade t) -> presentValue(t)) .collect(Collectors.toList()); ● Sometimes compiler needs a type hint Top Tip
  • 71. Streams ● Learn to love 'Collector' interface ● Complex, but useful ● Sometime necessary to write them ● Need collectors for Guava 'ImmutableList' and friends ○ see 'Guavate' class in OpenGamma Strata
  • 73. Interfaces ● Now have super-powers ● Default methods ○ normal method, but on an interface ● Static methods ○ normal static method, but on an interface ● Extend interfaces without breaking compatibility ● Cannot default equals/hashCode/toString
  • 74. Interfaces ● New macro-design options ● Instead of factory class, use static method on interface ● Instead of abstract class, use interface with defaults ● Result tends to be fewer classes and better API Top Tip
  • 75. Interfaces ● If factory method is static on interface ● And all API methods are on interface ● Can implementation class be package scoped? Best Practice
  • 76. Coding Style ● Use modifiers in interfaces ● Much clearer now there are different types of method ● Prepares for possible future with non-public methods Best Practice public interface Foo { public static of(String key) { … } public abstract getKey(); public default isActive() { … } }
  • 78. Date and Time ● New Date and Time API - JSR 310 ● Covers dates, times, instants, periods, durations ● Brings 80%+ of Joda-Time to the JDK ● Fixes the mistakes in Joda-Time
  • 79. Date and Time Class Date Time ZoneOffset ZoneId Example LocalDate ✔ ❌ ❌ ❌ 2015-12-03 LocalTime ❌ ✔ ❌ ❌ 11:30 LocalDateTime ✔ ✔ ❌ ❌ 2015-12-03T11:30 OffsetDateTime ✔ ✔ ✔ ❌ 2015-12-03T11:30+01:00 ZonedDateTime ✔ ✔ ✔ ✔ 2015-12-03T11:30+01:00 [Europe/London] Instant ❌ ❌ ❌ ❌ 123456789 nanos from 1970-01-01T00:00Z
  • 80. Date and Time ● Move away from Joda-Time ● Avoid java.util.Date and java.util.Calendar ● Use ThreeTen-Extra project if necessary ○ http://www.threeten.org/threeten-extra/ ● Focus on four most useful types ○ LocalDate, LocalTime, ZonedDateTime, Instant ● Network formats like XML/JSON use offset types ○ OffsetTime, OffsetDateTime Best Practice
  • 81. Date and Time ● Temporal interfaces are low-level ● Use concrete types Best Practice // prefer LocalDate date = LocalDate.of(2015, 10, 15); // avoid Temporal date = LocalDate.of(2015, 10, 15);
  • 83. Other features ● Base64 ● Arithmetic without numeric overflow ● Unsigned arithmetic ● StampedLock ● CompletableFuture ● LongAdder/LongAccumulator ● Enhanced control of OS processes
  • 84. Other Features ● Enhanced annotations ● Reflection on method parameters ● No PermGen in Hotspot JVM ● Nashorn JavaScript ● JavaFX is finally ready to replace Swing
  • 85. Try a Java 8 open source library ● JOOL ○ https://github.com/jOOQ/jOOL ● ThrowingLambdas ○ https://github.com/fge/throwing-lambdas ● Parts of OpenGamma Strata (strata-collect - Guavate) ○ https://github.com/OpenGamma/Strata ● But beware excessively functional ones ○ most push ideas that don't really work well in Java
  • 86. Immutability ● Favour immutable classes ● Lambdas and streams prefer this ● Preparation for value types (Java 10?) ● Use Joda-Beans to generate immutable "beans" ○ http://www.joda.org/joda-beans/
  • 88. Summary ● Java 8 is great ● Can be quite different to Java 7 and earlier ● Vital to rethink coding style and standards ○ methods on interfaces make a big difference ● Beware the functional programming/Scala dudes ○ a lot of their advice is simply not appropriate for Java