Lambdas and Laughs

Lambdas and Laughs Jim Bethancourt Houston JUG @jimbethancourt

Forward Looking Statement Ok, Not Really…

Topics Covered • Lambda Support • Lambda syntax • Interface enhancements • Convert inner class to Lambda • forEach& Streams • Method & Constructor References • Functional API

Download Links & IDE Support • Regular JDK download link • http://jdk8.java.net/download.html(for EAs) • Netbeans • IntelliJ • Eclipse

Maven Support <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>2.3.2</version>  <configuration> <source>1.8</source> <target>1.8</target> </configuration> </plugin>

Lambdas A lambda expression is like a method: it provides a list of formal parameters and a body—an expression or block—expressed in terms of those parameters. • Expressions: • s -> s.length() • (int x, int y) -> x+y • () -> 42 Assign lambda to functional interface: Runnable r1 = () ->System.out.println("My Runnable");

Lambdas Blocks: (x, y, z) -> { if (x==y) return x; else { int result = y; for (inti = 1; i < z; i++) result *= i; return result; }}

Typical Use Cases • Anonymous classes (GUI listeners) • Runnables / Callables • Comparator • Apply operation to a collection via foreach method • Chain operations on a collection with Stream API

MOAR !!! Monday Tuesday Jump-Starting Lambda [TUT3371]10:30 AM Hilton Yosimite B/C Lambda Under the Hood [CON4180]11 AM Hilton Imperial A Lambda Q&A Panel [CON3374]1:30 PM Hilton Yosimite B/C • Programming with Lambda Expressions in Java [CON1770]11 AM Hilton Imperial A • GS Collections and Java 8: Functional, Fluent, Friendly, and Fun [CON5423]11 AM Hilton Imperial B • Under the Hood of Java 8 Parallel Streams with an Oracle Solaris Dtrace [BOF1937] 9: 45 PM Moscone North 131

MOAR!!! Thursday • Lambda Programming Laboratory [HOL3373]2 PM Hilton Franciscan A/B • Lambda-izingJavaFX [CON3248]3:30 PM Hilton Plaza A

Effectively Final • For both lambda bodies and inner classes, local variables in the enclosing context can only be referenced if they are final or effectively final. • A variable is effectively final if its value is not reassigned after its initialization. • No longer need to litter code with final keyword

Interface Defender Methods • Interface methods with bodies • default keyword • More graceful API evolution • Interfaces have no state • Static methods not inherited • Can reference abstract method • Called “Extended Interfaces” if no abstract methods present

Super! • Extended Interfaces can extend other extended interfaces • Methods can be overridden • Can decorate parent definitions via super interface I1 { default void method1() {//do stuff}} interface I2 extends I1{ default voidmethod1() { super.method1(); //do new stuff }}

Specify the Parent Interface interface D1{ default void meth1() {//do stuff}} interface D2extends D1{ void default meth1() { super.method1(); //do new stuff}} interface D3extends D1{ void default meth1() { super.method1(); //do new stuff}} interface D4extends D2, D3{ void default meth1() { D2.super.method1(); //do new stuff}}

Convert Anonymous Class to Lambdafrom http://learnjavafx.typepad.com/weblog/2013/02/mary-had-a-little-%CE%BB.html // Anonymous inner class for event handling .onAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent e) {anim.playFromStart(); } })

Convert Anonymous Class to Lambda • .onAction((ActionEvent) -> {anim.playFromStart(); } }) • .onAction((e) -> {anim.playFromStart();})

Convert Anonymous Class to Lambda • .onAction((ActionEvent) -> {anim.playFromStart(); } }) • .onAction((e) -> {anim.playFromStart();}) • .onAction(e -> {anim.playFromStart(); }) • .onAction(e -> anim.playFromStart();)

MOAR!!! • Transforming Code to Java 8 [CON1772] Thursday 2:30 Hilton Imperial B

forEach • forEach() - available on Iterator & Map interfaces and their implementations • Allows for internal control of iteration of elements for possible parallel operation List<String> names =Arrays.asList(“Bill", “Ed", “Al"); names.forEach(e ->{System.out.println(e);}); But be careful!!!

MOAR!!! • GS Collections and Java 8: Functional, Fluent, Friendly, and Fun [CON5423]Monday 11 AM Hilton Imperial B • Autumn Collections: From Iterable to Lambdas, Streams, and Collectors [TUT3472]Tuesday 8:30 AM Hilton Yosemite A • New Tricks for Old Dogs: Collections in Java 8 [CON6309] Thursday 4 PM Hilton Imperial A

java.util.stream • Classes to support functional-style operations on streams of values • Stream<T> - A sequence of elements supporting sequential and parallel bulk ops

java.util.stream • Stream opened by calling • Collection.stream() • Collection.parallelStream() List<String> names = Arrays.asList("Bill", “Ed", “Al"); out(names.stream().filter(e -> e.length() >= 4 ) .findFirst().get()); Returns “Bill”

java.util.stream • All other interfaces in stream package accessible through Stream interface • Collector<T,R> - A (possibly parallel) reduction operation. • FlatMapper<T,U> - Maps element of type T to zero or more elements of type U.

MOAR!!! • Journey’s End: Collection and Reduction in the Stream API [TUT3836]Monday 8:30 AM Hilton Yosemite A • Programming with Streams in Java 8 [CON1771] Monday 4 PM Hilton Imperial A • Parallel Streams Workshop [CON3372]Wednesday 10 AM Hilton Yosemite A • Loads more!!!

java.util • Spliterator<T> provides traversal operations • Optional<T> • Returned by Stream’s aggregate methods find*(), reduce(), min(), max() • Call get() to get the value it’s holding

Method & Constructor References • A method reference is used to refer to a (static or instance) method without invoking it • Aconstructor reference is similarly used to refer to a constructor without creating a new instance of the named class or array type. • Specified with the :: (double colon) operator

Method & Constructor References • Provide a way to refer to a method /constructor without invoking it • Examples: System::getProperty "abc"::length String::length super::toString ArrayList::new int[]::new

Lambdas and Laughs