New Features in JDK 8
Ivan St. Ivanov
Dmitry Alexandrov
Martin Toshev
Agenda
• Lambda Expressions
• Other New Features in JDK 8
• JEPs and JDK 9 Development
Lambda Expressions
Lambdas
• Lambdas bring anonymous function types in Java
(JSR 335):
(parameters) -> {body}
• Example:
(x,y) -> x + y
Lambdas
• Lambdas bring anonymous function types in Java
(parameters) -> {body}
• Example:
(x,y) -> x + y
… well … Groovy (a superset of java) already
provides this …
Lambdas
• Lambdas can be used in place of functional
interfaces (interfaces with just one method such
as Runnable)
• Example:
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("It
runs !");
}
}
).start();
new Thread(() ->
{ System.out.println("It runs !");
}
).start();
Lambdas
• Examples of such functional interfaces:
java.lang.Runnable -> run()
java.util.concurrent.Callable -> call()
java.security.PrivilegedAction -> run()
java.util.Comparator -> compare(T o1, T o2)
java.awt.event.ActionListener ->
actionPerformed (ActionEvent e)
java.lang.Iterable ->
forEach(Consumer<? super T> action)
Lambdas
java.lang.Iterable ->
forEach(Consumer<? super T> action) ?!?
Isn't this breaking backward compatibility ?!?
Lambdas
java.lang.Iterable ->
forEach(Consumer<? super T> action) ?!?
Isn't this breaking compatibility ?!?
No - because forEach is an extension method.
Lambdas
Extension methods provide a mechanism for
extending an existing interface without breaking
backward compatibility.
public interface Iterable<T> {
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
}
Lambdas
• This essentially means that lambdas can be used
to replace all functional interfaces used in a
gazillion of libraries
• Moreover lambdas increase performance when
used instead of anonymous inner classes because
they are implemented with the invokedynamic
instruction
• In this regard many of the standard JDK class
are being refactored to use lambdas
Lambdas
• Additional functional interfaces are provided by
the java.util.function package for use by lambdas
such as:
o Predicate<T> - one method with param of type T and
boolean return type
o Consumer<T> - one method with param T and no
return type
o Function<T, R> - one method with param T and return
type R
o Supplier<T> - one method with no params and
return type T
Stream API
• Databases and other programming languages
allow us to specify aggregate operations explicitly
• The streams API provides this mechanism in the
Java platform
• The notion of streams is derived from functional
programming languages
Stream API
• The stream API makes use of lambdas and
extension methods
• Streams can be applied on collections, arrays, IO
streams and generator functions
Stream API
• Streams can be finite or infinite
• Streams can apply intermediate functions on the
data that produce another stream (e.g. map,
reduce)
Stream API
java.util.stream.Stream<T> collection.stream();
java.util.stream.Stream<T>
collection.parallelStream();
Useful methods:
o filter(Predicate), map(Function),
reduce(BinaryOperator), collect()
o sum(), min(), max(), count()
o anyMatch(), allMatch(), forEach(),
Stream internals
int sum = widgets.stream()
.filter(w -> w.getColor() == RED)
.mapToInt(w -> w.getWeight())
.sum();
• Stream operations are composed into a pipeline
• Streams are lazy: computation is performed when
the terminal operation is invoked
Method references
• Intended to be used in lambda expressions,
preventing unnecessary boilerplate
• Example:
books.stream().map(b -> b.getTitle()) 
books.stream().map(Book::getTitle)
• Lambda parameter list and return type must
match the signature of the method
Method references – static
methods
public class Printers {
public static void print(String s) {...}
}
Arrays.asList("a", "b", "c").forEach(Printers::print)
Method references – instance
methods (1)
public class Document {
public String getPageContent(int pageNumber) {
return this.pages.get(pageNumber).getContent();
}
}
public static void printPages(Document doc, int[]
pageNumbers) {
Arrays.stream(pageNumbers)
.map(doc::getPageContent)
.forEach(Printers::print);
}
Method references – instance
methods (2)
public class Document {
public String getPageContent(int pageNumber) {
return this.pages.get(pageNumber).getContent();
}
}
public static void printDocuments(List<Page> pages) {
pages.stream()
.map(Page::getContent)
.forEach(Printers::print);
}
Method references – constructors
public static Stream<Page>
createPagesFrom(Stream<String> contents) {
return contents.map(Page::new).
}
Lambda Expressions:
Hands-On-Lab
Lambdas Hands-on-Lab:
Overview
•
Environment setup
•
Concept
•
Task categories
Lambdas Hands-on-Lab:
Environment Setup
•
Download and install OpenJDK 8 early access
build from https://jdk8.java.net/lambda/
(… or build yours from the OpenJDK repo)
Lambdas Hands-on-Lab:
Environment Setup
•
Download and install an IDE:
o Eclipse
http://www.oracle.com/technetwork/articles/java/lambda1984522.html
(for Eclipse 4.3: Start IDE -> Install New Software)
http://build.eclipse.org/eclipse/builds/4P/siteDir/updates/4.3-Pbuilds
o IntelliJ IDEA CE
http://www.jetbrains.com/idea/free_java_ide.html
Lambdas Hands-on-Lab:
Environment Setup
•
Get the sources:
git clone https://github.com/AdoptOpenJDK/lambda-tutorial
or download
• Import the sources as Maven projects in the IDE
http://dmitryalexandrov.net/lambda.zip
• Set the Java 8 profile (source compatibility level)
• Check if the sources compile and that you are able to
run ConfigureYourLambdaBuildOfJdk
Lambdas Hands-on-Lab:
Concept
•
We have several classes and tests for them
•
Find “// your code here” and write the code !
•
Run the tests. Try to make them green!
(… read the comments.. They are useful !)
Lambdas Hands-on-Lab:
Task Categories
• Internal vs External Iteration
• Filtering and Collecting
• Mapping
• Method References
Lambdas Hands-on-Lab:
Internal vs External Iteration
Java 7 (External)
for (Shape shape: myShapes) {
shape.setColor(RED);
}
Java 8 (Internal)
myShapes.forEach(shape ->
shape.setColor(RED));
Lambdas Hands-on-Lab:
Filtering and Collecting
Java7
for (String s: otherThings) {
if (satisfiesSomeCondition(s)) {
things.add(s);
}
}
Java8
otherThings.stream()
.filter(s ->
satisfiesSomeCondition(s))
.collect(Collectors.toList());
Lambdas Hands-on-Lab:
Mapping
Java7
List<String> upperCaseStrings = new ArrayList<>();
for (String s: mixedCaseStrings) {
upperCaseStrings.add(s.toUpperCase());
}
Java8
mixedCaseStrings.stream()
.map(s -> s.toUpperCase())
.collect(Collectors.toList());
Lambdas Hands-on-Lab:
Mapping
Using a lambda expression:
myStrings.map(s -> s.toUpperCase());
Using a method reference:
myStrings.map(String::toUpperCase);
Can be used with:
• Static methods belonging to a particular class (<class>::<staticMethod>)
• Instance methods bound to a particular object instance (<obj> ::
<instanceMethod>)
• Instance methods bound to a particular class (<class> :: <instanceMethod>)
• Constructor belonging to a particular class (<class> :: new)
Lambdas Hands-on-Lab:
Default Methods
Java 8
public interface A {
default void foo(){
System.out.println("Calling A.foo()");
}
}
public class Clazz implements A {
}
Clazz clazz = new Clazz();
clazz.foo(); // Calling A.foo()
Lambdas Hands-on-Lab:
Default Methods
Java 8
public class Clazz2 implements A {
@Override
public void foo(){
System.out.println("Calling A.foo()");
}
}
Clazz2 clazz2 = new Clazz2();
clazz2.foo(); // Calling A.foo()
Lambdas Hands-on-Lab:
Let's have some fun
Lambdas Hands-on-Lab:
Hints
Examples:
The basic syntax of a lambda is either
(parameters) -> expression
1. (int x, int y) -> x + y
or
2. (x, y) -> x - y
(parameters) -> { statements; }
3. () -> 42
4. (String s) -> System.out.println(s)
5. x -> 2 * x
6. c -> { int s = c.size(); c.clear(); return s; }
7. myShapes.forEach(shape -> shape.setColor(RED));
8. otherThings.stream().filter(s ->
satisfiesSomeCondition(s)).collect(Collectors.toList()); 9.
mixedCaseStrings.stream().map(s -> s.toUpperCase()).collect(Collectors.toList());
10. myStrings.map(String::toUpperCase);
11. public interface A { default void foo(){ System.out.println("Calling A.foo()");} }
Other New Features in JDK 8
Date and Time API (JSR 310)
• Provides a new date, time and calendar API for
the Java SE platform
• Examples:
Clock clock = Clock.systemUTC();
ZoneId zone = ZoneId.systemDefault();
ZoneId customZone = ZoneId.of("Europe/Berlin");
Clock customClock = Clock.system(customZone);
DateTimeFormatter formatter = DateTimeFormatter.
ofPattern("MM-DD-YYYY");
LocalDate date = LocalDate.now();
String formattedDate = date.format(formatter);
System.out.println(formattedDate);
Nashorn (via JSR 223)
• Nashorn is a JavaScript engine developed in the
Java language
• A command line tool (jjs) for running javascript
without using Java is also provided
Nashorn (via JSR 223)
• Nashorn is a JavaScript engine developed in the
Java language
• A command line tool (jjs) for running javascript
without using Java is also provided
• … well … JDK 6 is already shipped with Mozilla's
Rhino JavaScript engine but is slower …
Nashorn (via JSR 223)
• Example (calling JavaScript from Java):
ScriptEngineManager m = new ScriptEngineManager();
ScriptEngine nashorn = m.getEngineByName("nashorn");
try {
nashorn.eval("print('Hello, world')");
} catch (ScriptException e) {
}
Nashorn (via JSR 223)
• Example (calling Java from JavaScript):
var ExampleType = Java.type("com.sample.Example");
var example = new ExampleType("arg");
print(example.method())
Parameter Names (JEP 118)
• Parameter names for method/constructor
parameters can be retrieved at runtime via
reflection
Method method = …
Parameter param = method.getParameters()[0];
System.out.println(param.getName());
Annotation on Java Types
(JSR 308, JEP 104)
• Extend the set of annotatable locations in the
syntax of the Java programming language
• Allow type checkers in the form of compiler plugins to provide stronger type checking
• Sample annotations: @notnull, @readonly
• Enhancements to JSR 269 (Pluggable
Annotation Processing API)
Repeating Annotations
(JEP 120)
• Change the Java programming language to allow
multiple annotations with the same type on a
single program element
Base64 Encoding/Decoding
(JEP 135)
• Defines a standard API for Base64 encoding and
decoding:
java.util.Base64.Encoder
java.util.Base64.Decoder
Concurrency Updates
(JEP 155)
• Scalable updatable variables (for frequent
updates from multiple threads) are part of the
concurrency updates:
java.util.concurrent.atomic.DoubleAccumulator
java.util.concurrent.atomic.DoubleAdder
java.util.concurrent.atomic.LongAccumulator
java.util.concurrent.atomic.LongAdder
Compact Profiles
(JEP 161)
• Defines a few subset Profiles of the Java SE
Platform Specification so that applications that do
not require the entire Platform can be deployed
and run on small devices.
• Currently three profiles:
o compact1
o compact2
o compact3
Other
• Prepare for modularization (JEP 162) - changes
and deprecation of APIs to prepare for the
modularization of the platform as undertaken by
project Jigsaw
• Permanent generation space removed - objects
from this space such as class metadata, static
variables and interned strings moved to heap
space
(improved convergence between OpenJDK and Oracle's JRockit)
Some books
JEPs and JDK 9 Development
JEPs and JDK 9 Development
So lets see what JEPs are left for JDK 9 ->
http://openjdk.java.net/jeps/
Q&A
References
OpenJDK 8 early access builds
https://jdk8.java.net/
Oracle JDK 8 early access builds
http://www.oracle.com/technetwork/java/javase/d
ownloads/ea-jsp-142245.html
Eclipse with JDK 8 support
https://wiki.eclipse.org/JDT_Core/Java8
References
OpenJDK mercurial repositories
http://hg.openjdk.java.net/
OpenJDK 9 build instructions
http://hg.openjdk.java.net/jdk9/jdk9/rawfile/tip/README-builds.html
JSR 337: Java SE 8 (Early Draft Review Specification)
http://cr.openjdk.java.net/~mr/se/8/java-se-8edr-spec.html
References
Lambda tutorial
https://github.com/AdoptOpenJDK/lambda-tutorial
State of the Lambda
http://cr.openjdk.java.net/~briangoetz/lambda/lam
bda-state-final.html
Lambda FAQ
http://www.lambdafaq.org/
References
Java SE tutorials: Lambda Expressions
http://docs.oracle.com/javase/tutorial/java/javaOO
/lambdaexpressions.html
Lambda Quick Start Guide
http://www.oracle.com/webfolder/technetwork/tu
torials/obe/java/Lambda-QuickStart/index.html
Java Enhancement Proposals
http://openjdk.java.net/jeps