Java 8

JAVA 8
Features and other cool stuff

A bit of history
● (“1.0”) -> LocalDate.of(1996, Month.JANUARY, 23)
● (“1.1”) -> LocalDate.of(1997, Month.FEBRUARY, 19)
● (“1.2”) -> LocalDate.of(1998, Month.DECEMBER, 9)
● (“1.3”) -> LocalDate.of(2000, Month.MAY, 8)
● (“1.4”) -> LocalDate.of(2002, Month.FEBRUARY, 6)
● (“1.5”) -> LocalDate.of(2004, Month.SEPTEMBER, 30)
● (“1.6”) -> LocalDate.of(2006, Month.DECEMBER, 11)
● (“1.7”) -> LocalDate.of(2011, Month.JULY, 7)
● (“1.8”) -> LocalDate.of(2014, Month.MARCH, 15)

JAVA 8, what more ?
● JAVA 8 is for JAVA 7 what JAVA 5 was for JAVA 1.4
● Lot’s of cool stuff
● Finally fonctional programming oriented
● With great power comes great responsability
● Ok, let’s dive into

Lambdas : let’s blow your mind

Lambdas : let’s blow your mind
Arrays.asList( "a", "b", "d" ).forEach( ( String e ) -> System.out.println( e ));
Arrays.asList( "a", "b", "d" ).forEach( e -> {
System.out.print( e );
System.out.print( e );
} );
Arrays.asList( "a", "b", "d" ).forEach( e -> System.out.println( e ) );

Lambdas : some explanations
● Anonymous method
● To unlearn what you’ve learned, you have to
● (argtype arg...) -> { return some expression.. probably using these arguments }
● Type inference : JVM compiler guess for you args types
● Welcome to functional programming !

Functional interfaces : let’s be friends

Functional interfaces : let’s be friends
● Interfaces with only ONE abstract method
● Can contains static and default method (next slide, don’t panic)
● Most of generic functional use case already in java.util.function package
○ Function, Supplier, Consumer, Predicate, etc.
● The backbone of lambda
@FunctionalInterface
public interface Functional {
void method();
}

Interface’s Default/Static Methods

Interface’s Default Methods : abstract death ?
● Not required to be implemented
● Inherited by default
● Overridden allowed
● Public visibility only

Interface’s Default Methods : abstract death ?
private interface Defaulable {
// Interfaces now allow default methods, the implementer may or
// may not implement (override) them.
default String notRequired() {
return "Default implementation";
}
}
private static class DefaultableImpl implements Defaulable {
}
private static class OverridableImpl implements Defaulable {
@Override
public String notRequired() {
return "Overridden implementation";
}
}

Interface’s Static Methods : tooling in interface
● Act as static class method
● An interface can now contain all the tooling
private interface DefaulableFactory {
// Interfaces now allow static methods
static Defaulable create( Supplier< Defaulable > supplier ) {
return supplier.get();
}
}

Method References : let’s take some shortcuts

Method References : let’s take some shortcuts
● Another way, more concise, to refer directly to existing methods
● Constructor reference
● Static method reference
● Instance method reference
● Instance method reference using Class

Method reference : example please !
public class Example {
public int add(int a, int b) {
return a + b;
}
public static int mul(int a, int b) {
return a * b;
}
public String lower(String a) {
return a.toLowerCase();
}
public void printDate(Date date) {
System.out.println(date);
}
public void oper(IntBinaryOperator operator, int a, int b) {
System.out.println(operator.applyAsInt(a, b));
}
public void operS(Function<String, String> stringOperator, String a) {
System.out.println(stringOperator.apply(a));
}
public GregorianCalendar operC(Supplier<GregorianCalendar> supplier) {
return supplier.get();
}
}

Constructor reference
ex.operC(()->{ return new GregorianCalendar();})
ex.operC(GregorianCalendar::new);
● Lambda way
● Method reference way

Static method reference
● Lambda way
ex.oper((a, b) -> Example.mul(a, b), 1, 2);
ex.oper(Example::mul, 1, 2);

Instance method reference
● Lambda way
ex.oper((a, b) -> ex.add(a, b), 1, 2);
ex.oper(ex::add, 1, 2);

Instance method reference using class
● Lambda way
ex.operS(String::toLowerCase, "STRING");
ex.operS(s->s.toLowerCase(), "STRING");

Method References : WARNING !!!
Should be assignable to a functionnal interface

Repeating annotations : hide me this

Repeating annotations : hide me this
● Same annotation can be repeat several times
● How to
@Schedule(dayOfMonth="last")
@Schedule(dayOfWeek="Fri", hour="23")
public void doPeriodicCleanup() { ... }
@Repeatable(Schedules.class)
public @interface Schedule {
String dayOfMonth() default "first";
String dayOfWeek() default "Mon";
int hour() default 12;
}
public @interface Schedules {
Schedule[] value();
}

Extended Annotations Support : annotation everywhere !

Extended Annotations Support : annotation everywhere !
● ElementType.TYPE_USE -> Annotation on type use
● ElementType.TYPE_PARAMETER -> Annotation on type variable
@NonNull String name; // Type use
List<@NonNull String> names; // Type parameter
class UnmodifiableList<T> implements @Readonly List<@Readonly T>
{...}
email = (@Email String) input;
new @Information MyObject();
void doSomething() throws @ImportantForMe MyException { ... }

Parameter names : for reflection lovers only

Parameter names : for introspection lovers only
JVM arg : -parameter

Optional is not an option : end of NullPointer ?

Optional< String > fullName = Optional.ofNullable( null );
System.out.println( "Full Name is set? " + fullName.isPresent() );
System.out.println( "Full Name: " + fullName.orElseGet( () -> "[none]" ) );
System.out.println( fullName.map( s -> "Hey " + s + "!" ).orElse( "Hey Stranger!" ) );
Full Name is set? false
Full Name: [none]
Hey Stranger!

Optional< String > firstName = Optional.of( "Tom" );
System.out.println( "First Name is set? " + firstName.isPresent() );
System.out.println( "First Name: " + firstName.orElseGet( () -> "[none]" ) );
System.out.println( firstName.map( s -> "Hey " + s + "!" ).orElse( "Hey Stranger!" ) );
First Name is set? true
First Name: Tom
Hey Tom!

Streams : THIS IS map/reduce !!!

● Create a pipeline made of operations
● Terminal operation could produce another data store
● Parallelization

final Collection< Task > tasks = Arrays.asList(
new Task( Status.OPEN, 5 ),
new Task( Status.CLOSED, 8 )
);
// Calculate total points of all active tasks using sum()
final long totalPointsOfOpenTasks = tasks
.stream()
.filter( task -> task.getStatus() == Status.OPEN )
.mapToInt( Task::getPoints )
.sum();
System.out.println( "Total points: " + totalPointsOfOpenTasks );
Total points: 18

);
// Group tasks by their status
final Map< Status, List< Task > > map = tasks
.stream()
.collect( Collectors.groupingBy( Task::getStatus ) );
System.out.println( map );
{CLOSED=[[CLOSED, 8]], OPEN=[[OPEN, 5], [OPEN, 13]]}

);
// Calculate the weight of each tasks (as percent of total points)
final Collection< String > result = tasks
.stream() // Stream< String >
.mapToInt( Task::getPoints ) // IntStream
.asLongStream() // LongStream
.mapToDouble( points -> points / totalPoints ) // DoubleStream
.boxed() // Stream< Double >
.mapToLong( weigth -> ( long )( weigth * 100 ) ) // LongStream
.mapToObj( percentage -> percentage + "%" ) // Stream< String>
.collect( Collectors.toList() ); // List< String >
System.out.println( result );
[19%, 50%, 30%]

Date/Time API : Joda time was here...

● Inspired by JODA Time : made by developpers for developpers
● One package : java.time
● IMMUTABLE by design
Date/Time API : Joda time was here...

Date/Time API : Clock
// Get the system clock as UTC offset
final Clock clock = Clock.systemUTC();
System.out.println( clock.instant() );
System.out.println( clock.millis() );
2014-04-12T15:19:29.282Z
1397315969360

Date/Time API : LocalDate / LocalTime
// Get the local date and local time
final LocalDate date = LocalDate.now();
final LocalDate dateFromClock = LocalDate.now( clock );
System.out.println( date );
System.out.println( dateFromClock );
// Get the local date and local time
final LocalTime time = LocalTime.now();
final LocalTime timeFromClock = LocalTime.now( clock );
System.out.println( time );
System.out.println( timeFromClock );
2014-04-12
2014-04-12
11:25:54.568
15:25:54.568

Date/Time API : ZoneDateTime
// Get the zoned date/time
final Clock clock = Clock.systemUTC();
final ZonedDateTime zonedDatetime = ZonedDateTime.now();
final ZonedDateTime zonedDatetimeFromClock =
ZonedDateTime.now( clock );
final ZonedDateTime zonedDatetimeFromZone =
ZonedDateTime.now( ZoneId.of( "America/Los_Angeles" ) );
System.out.println( zonedDatetime );
System.out.println( zonedDatetimeFromClock );
System.out.println( zonedDatetimeFromZone );
2014-04-12T11:47:01.017-04:00
[America/New_York]
2014-04-12T15:47:01.017Z
2014-04-12T08:47:01.017-07:00
[America/Los_Angeles]

Date/Time API : Duration
// Get duration between two dates
final LocalDateTime from =
LocalDateTime.of( 2014, Month.APRIL, 16, 0, 0, 0 );
final LocalDateTime to =
LocalDateTime.of( 2015, Month.APRIL, 16, 23, 59, 59 );
final Duration duration = Duration.between( from, to );
System.out.println( "Duration in days: " + duration.toDays() );
System.out.println( "Duration in hours: " + duration.toHours() );
Duration in days: 365
Duration in hours: 8783

And so many other things
● Nashorn JavaScript Engine : evaluate JavaScript in JAVA
● Base64 standard support
○ URL-friendly encoder/decoder
○ MIME-friendly encoder/decoder
● Parallel Arrays
● Class dependency analyzer : jdeps
● XX:PermSize / XX:MaxPermSize respectivly replaced by XX:MetaSpaceSize
/ XX:MaxMetaSpaceSize
● String.join() / Objects.nonNull()
● Reflection api support TypeName, GenericString, access Generic type, etc.
● ...

Java 8

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Java 8

Similaire à Java 8 (20)

Plus de Cédric GILLET

Plus de Cédric GILLET (6)

Dernier

Dernier (20)

Java 8