50 new things we can do with Java 8
José Paumard
Date
- Instant.now()
- Duration.between(start, end).toMillis()
- LocalDate.now() — .of() —
- Period: time between 2 dates
- now.with(TemporalAdjuster.next(DayOfWeek.SUNDAY));
- LocalTime.now() — of(10,20) //10:20
- ZoneTime / ZoneId.of(“Europe/London”)
- ZonedDateTime — Period
- Formatter (DateTimeFormatter.ISO_DATE_TIME etc.)
- Bridge with java.util.Date:
- Date.from(instant)
- TimeStamp.from(instant)
- Date.from / toLocalDate()
Stream
- IntStream
- Patter.compile(…).splitAsStream(txt)
String concat
- compiler does stringbuilder conversion
- StringJoiner: concat with delimeters + pre-/postfix
- String.join(…)
Numbers
- Long.max(), Long.sum()
- lambda: .reduce(…,Long::max)
- static Long.hashCode(l)
I/O reading text files
- Files.lines(Path)
- path=Paths.get(…);
- autoclosable with try(resource){} pattern
- Files.list(path)
- Files.walk(path): recursive find
Iterable
- forEach consumes (e.g; strings.forEacht(System.out::println))
- boolean b = list.removeIf(s-> s.length() > 4)
- list.replaceAll(String::toUpperCase)
- list.sort(Comparator.naturalOrder())
Comparator
- Comparator.naturalOrder()
- Comparator.comparingBy(Person::getLastName) .thenComparing(Person::getFirstName).thenComparing(..)
- comparator.reversedOrder() / comp.reversed()
- Comparator.nullsFirst() /nullsLast()
Optional
- Optional.
empty(); - Optional.of(“one”)
- opt.isPresent() /.get() / .orElse(“”) / .orElseThrow()
- Stream integration ifPresent / filter / map / flatMap
- flatMap().collect(…)
Map
- map.forEach( (key, value) -> …)
- better Compare-And-Swap functions for concurrency:
- map.get(key) -> map.getOrDefault(key, default)
- map.putIfAbsent(key, object)
- map.replace(key, old, new) -> extra test on old value
- map.remove(key, old) - extra test on old value
- map.compute() / computeIfAbsent() / computeIfPresent()
Type Annotations
- @NonNull
Parallel Arrays
- Arrays.parallelPrefix
- parallelSort
Completable Future -> graphs of tasks (“reactive programming”)
- CompletableFuture.supplyAsync()
- thenApply() thenAccept()
- thenCompose()
- allof(): combine multiple futures -> join()
- thenCombine() / applyToEither: get the first result
Atomic Variables
- AtomicLong -> updateAndGet(lambda) / accumulateAndGet(lambda)
- multithreaded ;increment() / .sum() computes final result
StampedLock
- s.writeLock() s.readLock()
- tryOptimisticRead()
ConcurrentHashMap
- completely replaced, no locking
size(): do not use! -> map.mappingCount()- search(threshold, lambda) : threshold before going parallel
- reduce() / reduceKey() / reduceEntries()
- ConcurrentHashMap.newKeySet() // values are Boolean.TRUE
Books
- Java SE8 for the Really Impatient - Cay Horstman
Introduction to Android Wear - A Glimpse Into the Future
Cyril Mottier
principles:
- contextual
- glanceable
- low interaction
In Full Flow: Java 8 Lambdas in the Stream
Paul Sandoz
Stream Basics
- Stream:
- abstract view over data
- aggregate ops
- not RxJava, not CompletableFuture, not Distributed Stream
- e.g.;
- list.stream().filter(s -> s.length() > 0).count()
- mapToLong(e -> 1L)
- reduce(0, Long::sum);
- reduce(“”, (a, b) -> a + “ “ + b)
- Optional
- performance:
- parallel can go slower for small datasets (due to overhead)
- reduce can generate a lot of extra classes -> .collect()
Parallel Game
- a stream is sequential by default
- can be made parallel()
- Greedy -> takes more work -> multicore
- implementation under the hood:
- forkjoinpool -> split problem in parts
- when to use?
- http://gee.cs.oswego.edu/dl/html/StreamParallelGuidance.html
- minimum threshold (~100µs)
- workload ‘components’
- measure
- JMH — http://openjdk.java.net/projects/code-tools/jmh/
- switch off HyperThreading
- visualize
- -> DOT file -> SVG
- adapt() / peek(): to get feedback
- datamodels:
- ArrayList / Range: best
- HashSet: not completely balanced
- LinkedList / iterator: poor choice (size unknown)
- boxing:
- gc works harder
- pointer chasing/ cache issues
- -> Int/Long Streams
The future
- near term:
- better parallel resource control
- improved splitting implementations
- Files.lines()
- unordered input to limit()
- more operations:
- takeWhile()
- skipWhile()
- Matcher.stream()
- helper methods
- Optional.stream()
- Stream.ofNullable(T t)
- longer term:
- Value types
- extending generics over values
- IntStream extends Stream
- Tuples
