This document summarizes some of the new features introduced in Java 8, including streams, lambda expressions, default methods, and date/time API changes. It discusses streams in more detail, covering stream operations like filter, map, distinct, and collect. It also covers new features like Optional for returning absent/present values, annotations for null checks, parallel array sorting, and concurrency utilities.

1. What’s new in Java 8
Maxim Zakharenkov
3 April, 2014

2. Existing presentations
• Новое в JDK 8. Александр Ильин, Oracle
https://www.youtube.com/watch?v=lSnNWRABA1s
• JDK8: Stream style, Sergey Kuksenko, Oracle
http://www.slideshare.net/SergeyKuksenko/jdk8-stream-style
• More on slideshare

3. What this talk is about
• Streams
• Stream notes
• Some other new features in Java 8
– Optional<?>
– Annotations
– parallelSort
– Concurrency
– Some other stuff

4. Streams
Other presentation slides here

13. filter()

14. filter()
map()

15. filter()
map()
map()

16. filter()
map()
map()
distinct()

17. filter()
map()
map()
distinct()collect()

18. Stream notes: Short circuiting
Random random = new Random();
int[] result = IntStream
.generate(() ->random.nextInt())
.sorted()
.toArray();

19. Stream notes: parallel forEach
DEMO

20. Stream notes: parallel forEach
• forEach does not preserve order!
• Use forEachOrdered if order matters

21. Stream notes: not reusable
IntStream stream = Arrays.stream(new int[]{1, 2, 3, 4});
List<Object> list = stream.boxed().collect(Collectors.toList());
// this throws java.lang.IllegalStateException
double average = stream.average().getAsDouble();

22. Optional results 1
public String findById(int id) {
// ...
return …;
}

23. Optional results 2
public String findById(int id) {
// ...
return …;
}
String result = findById(10);

24. Optional results 3
public String findById(int id) {
// ...
return …;
}
String result = findById(10);
prefix = result.substring(0, 3);

25. Optional results 4
public String findById(int id) {
// ...
return …;
}
String result = findById(10);
if(result != null) {
prefix = result.substring(0, 3);
}

26. Optional results 5
public String ? findById(int id) {
// ...
return …;
}
String result = findById(10);
prefix = result.substring(0, 3);

27. Optional results 6
public Optional<String>
findById(int id) {
// ...
return …;
}
if(result.isPresent()) {
}

28. Annotations
public @NonNull String findById(int id) {
// ...
return …;
}

29. Checker framework
http://types.cs.washington.edu/checker-
framework/current/checkers-manual.html

30. Checker framework
• @Interned String intern() { ... } // return value
• int compareTo(@NonNull String other) { ... } // parameter
• String toString(@ReadOnly MyClass this) { ... } // receiver
• @NonNull List<@Interned String> messages; // generics: non-
null list of interned Strings
• @Interned String @NonNull [] messages; // arrays: non-null
array of interned Strings
• myDate = (@ReadOnly Date) readonlyObject; // cast

31. Arrays.parallelSort
• Works faster
• Everyting has own cost
– DualPivotQuickSort - sequental
– MergeSort - parallel

32. Parallel sort of 50M elements
(on my 4 core laptop)
• Single threaded DualPivotQuickSort: 47sec
• Parallel merge sort: 21sec
• Sequential stream: 95sec
• Parallel stream: 104sec

33. Parallelism, is it good or bad?
(example)
• 2 CPU
• Concurrent clients - 1000 queries per second
• Single sequential sort - 2ms
• Single parallel sort - 1ms + sync overhead ~1.2ms
• Less transactions per second with parallel sort
• Parallel algorithms do not always fit well

34. HashMap
0 key1
1
2
3
4
5
6
key2
key3

35. HashMap before Java 8
0 key1
1
2
3
4
5
6
key2
key3
key4 key4

36. HashMap in Java 8
0 key1
1
2
3
4
5
6
key2
key3
key4
key4

37. MissionControl
• Cool tool for JVM diagnostics
• Comes with JDK installation (jmc executable
• Now we have 3 similar tools in JDK
– jconsole
– jvisualvm
– jms

38. Future of frameworks
• Type-safe property references in Hibernate-
like query languages
• JUnit, Mockito-like frameworks with method
references
• Event handlers
• Better XML and JSON serializers
• - ….

39. QA