Post on 15-Jul-2015
What’s new in Java 8Kyle Smith
linkedin.com/in/kylesm
@kylesm
• Concurrency improvements
• Default methods
• Functional interfaces
• Lambda expressions
• Method references
• Streams
• Date/time
• Optional
• JavaScript
• JVM PermGen
• Base64 support
• Compact profiles
• Annotation improvements
• Type inference improvements
• Method parameter reflection
• JDBC 4.2
• Concurrency improvements
• Default methods
• Functional interfaces
• Lambda expressions
• Method references
• Streams
• Date/time
• Optional
• JavaScript
• JVM PermGen
• Base64 support
• Compact profiles
• Annotation improvements
• Type inference improvements
• Method parameter reflection
• JDBC 4.2
Themes
• ConcurrentHashMap — all new (inside)!
• LongAdder, DoubleAdder
• StampedLock
• CompletableFuture
Adders
• New classes for concurrent counters
• Waaaayyy more scalable than AtomicLong,etc.
• …if you can tolerate some inaccuracy
LongAdder clicks = new LongAdder();
clicks.increment();
// or counter.add(long)
// ...
clicks.sum();
StampedLock
• Alternative to ReentrantReadWriteLock
• “does not consistently prefer readers over writers or
vice versa"
• Provides optimistic reads
void move(double deltaX, double deltaY){
long stamp = sl.writeLock();
try {
x += deltaX;
y += deltaY;
} finally {
sl.unlockWrite(stamp);
}
}
double distanceFromOrigin() {
long stamp = sl.tryOptimisticRead();
double currentX = x, currentY = y;
if (!sl.validate(stamp)) {
stamp = sl.readLock();
try {
currentX = x;
currentY = y;
} finally {
sl.unlockRead(stamp);
}
}
return Math.sqrt(currentX * currentX
+ currentY * currentY);
}
CompletableFuture
• Everybody wants to be event-driven & reactive
• CompletableFuture allows composition of async
work
CompletableFuture<String> f1 = //…
CompletableFuture<Double> f2 = f1
.thenApply(Integer::parseInt)
.thenApply(r -> r * r * Math.PI);
Default methods
• Interfaces can supply non-abstract methods
• Enables existing interfaces to evolve
• Eliminates the need for companion (“garbage”)
classes
// java.lang.Iterable
default void forEach(Consumer<? super T>
action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
Functional interfaces
• Any interface with a single abstract method
• Examples:
• java.util.Comparator
• java.lang.Runnable
• Can be annotated with @FunctionalInterface
Lambda expressions
• Function values in Java
• Compatible with a functional interface when their
shapes match
• Syntax: (parameters) -> expression
DoubleUnaryOperator op1 =
(double r) -> r * r * Math.PI;
DoubleUnaryOperator op2 =
(r) -> r * r * Math.PI;
Runnable r =
() -> System.out.println("Hi, NEJUG!");
void cut(List<String> l, int len) {
l.replaceAll(s -> s.substring(0, len));
}
Streams
public Collection<Person>
findStudents(List<Person> people) {
Collection<Person> students =
new ArrayList<>();
for (Person p : people) {
if (p.isStudent()) {
students.add(p);
}
}
return students;
}
public Collection<Person>
findStudents(List<Person> people) {
Collection<Person> students =
new ArrayList<Person>();
people.forEach(i -> {
if (i.isStudent()) {
students.add(i);
}
});
return students;
}
public Collection<Person>
findStudents(List<Person> people) {
return people
.stream()
.filter(p -> p.isStudent())
.collect(Collectors.toList());
}
• “ A sequence of elements on which one or more
operations can be performed”
• Operations are either intermediate or terminal
• Streams can be sequential or parallel
• Intermediates:
• map, filter, flatMap, sorted, allMatch, anyMatch,
findAny, findFirst, flatMap, …
• Terminal:
• collect, count, forEach,reduce, max, min, …
long count = values
.stream()
.sorted()
.count();
long count = values
.parallelStream()
.sorted()
.count();
What next?
• Download JDK 8 from java.oracle.com
• IDE Support:
• Eclipse 4.3.2 SR2 (with patches!)
• IntelliJ IDEA 12.0+
• NetBeans IDE 8.0
Can’t move to Java 8?
• Google Guava (Java 6+)
• jsr166e (Java 6+)
• CHMv8, F/J tweaks, StampedLock, etc.
• Mix in some Groovy
• GPars