Java 8 will finally deliver us to the promised land of functional programming! So can we stop worrying now about learning Scala and Clojure and the other new kids on the block? We'll look at what new powers the new features such as Lambdas, Default Methods and Streams give us, as well as what Java is still lacking compared to other functional languages on the JVM.

1. Java 8 to the rescue!?
JavaZone 2013
1
torsdag 12. september 13

2. 2
RETURNOF
THE AVA
J
JAVA EIGHT
torsdag 12. september 13

3. Fredrik Vraalsen
vraalsen@iterate.no
Dad,
Java developer,
Scala enthusiast,
sci-fi fan, photo geek
and Age of Conan
assassin
@fredriv
© Fredrik Vraalsen 2008
torsdag 12. september 13

4. Java 8 – what’s new?
Lambdas, Extension Methods, SAMs, Streams, Method Handles, Oh My!
Nashorn JS engine
JSR-310: Date & time API
No more PermGen– where classloaders go to die
Compact profiles
...
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torsdag 12. september 13

5. Java 8 – what’s new?
Lambdas, Extension Methods, SAMs, Streams, Method Handles, Oh My!
Nashorn JS engine
JSR-310: Date & time API
No more PermGen– where classloaders go to die
Compact profiles
...
5
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6. Your Mission
Should you choose to accept it
Sort a list of people
by their names
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7. Java 7
List<Person> people = ...
Collections.sort(people);
7
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8. Java 7
Collections.sort(people, new Comparator<Person>() {
});
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9. Java 7
Collections.sort(people, new Comparator<Person>() {
public int compare(Person x, Person y) {
}
});
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10. Java 7
Collections.sort(people, new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
});
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11. We are not amused
© Fredrik Vraalsen 2012
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12. Java 7
Collections.sort(people, new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
});
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13. Java 7
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
Collections.sort(people, byName);
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14. Java 7
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
sort(people, byName);Collections.
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15. sort(people, byName)
Java 7
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
( , ;
Lisp?
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16. What about Java 8?
© Fredrik Vraalsen 2012
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17. Java 8
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
sort(people, byName);
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18. Java 8
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
people.sort(byName);
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19. Java 8
19
java.util.List:
default void sort(Comparator<? super E> c)
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20. Java 8
Defender Method
Default Method
(Virtual) Extension Method
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java.util.List:
default void sort(Comparator<? super E> c)
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21. Java 8
java.util.List:
default void sort(Comparator<? super E> c) {
}
Defender Method
Default Method
(Virtual) Extension Method
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22. Java 8
java.util.List:
default void sort(Comparator<? super E> c) {
Collections.sort(this, c);
}
Defender Method
Default Method
(Virtual) Extension Method
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23. Extension method
Extend interfaces with new methods
Compatibility
Default implementation
Override
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24. C# extension methods
Static methods
Cannot be overridden
One-size fits all solution
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25. Scala Traits
“Interfaces on steroids”
Method implementations
Variables
Everything a class can have – except constructors
Can mix in multiple traits
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26. Ok, nice...
What else?
© Fredrik Vraalsen 2012
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27. Java 8
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
Single Abstract Method
(SAM)
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28. Single Abstract Method
Interface with only one (non-default) method
Abstract class with only one abstract method
Sound familiar?
Pretty much every event listener, callback mechanism, ...
Can be replaced by a Lambda
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29. Lambda
Closure
Anonymous function
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30. SAM
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
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31. SAM
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
BodyReturn type
Parameter list
Method name
Type
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32. Lambda
Comparator<Person> byName = new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
};
BodyReturn type
Parameter list
Method name
Type
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33. Lambda
Comparator<Person> byName =
return x.getName().compareTo(y.getName());
};
BodyReturn type?
Parameter list
(Person x, Person y) -> {
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34. Lambda
Comparator<Person> byName =
(Person x, Person y) ->
Parameter list
BodyReturn type?
x.getName().compareTo(y.getName());
{
};
return
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35. Lambda
Comparator<Person> byName =
Parameter list
BodyReturn type?
(x, y) -> x.getName().compareTo(y.getName());(Person x, Person y)
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36. Lambda – putting it together
Comparator<Person> byName =
(x, y) -> x.getName().compareTo(y.getName());
people.sort(byName);
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37. Lambda – putting it together
people.sort((x, y) -> x.getName().compareTo(y.getName()));
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38. Lambda vs Java 7
Collections.sort(people, new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
});
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39. Lambda vs Java 7
Collections.sort(people, new Comparator<Person>() {
public int compare(Person x, Person y) {
return x.getName().compareTo(y.getName());
}
});
vs
people.sort((x, y) -> x.getName().compareTo(y.getName()));
39
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40. Cool!
Now onwards... © Fredrik Vraalsen 2013
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41. Method handles
Reference to methods
Can be used in place of lambdas
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42. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
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43. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
Comparator<Person> byName =
(Person a, Person b) -> a.compareByName(b);
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44. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
Comparator<Person> byName =
(a, b) -> a.compareByName(b);
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45. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
Comparator<Person> byName = Person::compareByName;
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46. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
Comparator<Person> byName = Person::compareByName;
people.sort(byName);
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47. Method handles
class Person { ...
public int compareByName(Person other) {
return name.compareTo(other.name);
}
}
people.sort(Person::compareByName);
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48. So far, so good?
Extension methods
Lambdas
Method handles
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49. So, what’s the catch?© Fredrik Vraalsen 2012
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50. What’s wrong with using List::sort ?
Modifies existing collection
Others may be using it?
Concurrency issues
Performance
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51. Streams
© Fredrik Vraalsen 2008
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52. The old fashioned way
List<String> namesOfAdults = new ArrayList<>();
for (Person p : people) {
if (p.getAge() >= 18) {
namesOfAdults.add(p.getName());
}
}
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53. Streams
Stream<Person> stream = people.stream();
Stream<Person> adults = stream.filter(p -> p.getAge() >= 18);
Stream<String> namesOfAdults =
adults.map(Person::getName);
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54. Streams – compose
Stream<String> namesOfAdults = people.stream().
filter(p -> p.getAge() >= 18).
map(Person::getName);
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55. Streams – collect
List<String> namesOfAdults = people.stream().
filter(p -> p.getAge() >= 18).
map(Person::getName).
collect(Collectors.toList());
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56. Streams – collect
List<String> namesOfAdults = people.stream().
filter(p -> p.getAge() >= 18).
map(Person::getName).
collect(toList());
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57. Performance
© Fredrik Vraalsen 2012
torsdag 12. september 13

58. Streams – performance
List<String> namesOfAdults = people.stream().
filter(p -> p.getAge() >= 18).
map(Person::getName).
collect(toList());
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59. Streams – performance
List<String> namesOfAdults = people.parallelStream().
filter(p -> p.getAge() >= 18).
map(Person::getName).
collect(toList());
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60. Scala FTW!
val namesOfAdults = people.
filter(p => p.age >= 18).
map(p => p.name)
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61. Scala FTW!
val namesOfAdults = people.
filter(_.age >= 18).
map(_.name)
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62. Scala FTW!
val namesOfAdults = people.filter(_.age >= 18).map(_.name)
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63. Scala FTW!
val namesOfAdults = people.par.filter(_.age >= 18).map(_.name).toList
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64. Streams – sorting
List<Person> sorted = people.stream().
sort(Person::compareByName).
collect(Collectors.toList());
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65. Scala FTW 2!
val sorted = people.sortBy(_.name)
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66. Streams – pipelines
Source
collection, array, generator function, IO channel, ...
Intermediate operations (Stream-producing)
filter, map, ...
Terminal operations (value-producing)
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67. Streams
java.util.stream
Create new results
Lazy
Parallelizable
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68. Ready to
make the jump!?
© Fredrik Vraalsen 2013
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69. Play with it!
Download from http://jdk8.java.net/download.html
Whitepapers at http://openjdk.java.net/projects/lambda/
FAQ http://www.lambdafaq.org/
Supported in IntelliJ IDEA 12 (and NetBeans nightlies?)
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70. Why use X instead?
Java 8 not yet released (duh!)
March 2014?
Will be a long time before you can use it in enterprise dev!
Clojure and Scala available NOW! (JDK 1.5 and 1.6)
Important things are still missing
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71. What’s missing?
© Fredrik Vraalsen 2012
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72. What’s missing?
Immutability
Value types
Immutable data structures
Lists, maps, sets, etc.
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73. What’s the big deal?
Functional programming is all about values!
And transformations (functions) computing new values
Concurrency
Parallelism
Robustness
Testability
Better / higher abstractions
Less code, less bugs!
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74. Some help to be found
Immutable collections
Google Guava, FunctionalJava
Concurrency mechanisms
Akka (Actors, STM)
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75. What else is missing?
Type inference
Pattern matching
For comprehensions
Named and default parameters
Properties
Implicit parameters / conversions
and much more...
http://stackoverflow.com/questions/3844745/scala-advantages-after-java-having-closures/3844844#3844844 75
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76. LambdaJ
Easier manipulation of collections and more, limited closure support
Google Guava
Lots of nice utility classes, some functional programming support
FunctionalJava
Most “pure” FP – but slow, separate collection hierarchy
Funcito
Simplify creation of functions from existing methods
Integrates with Guava, FunctionalJava, Jedi, ...
But I’m stuck in Java 6... Help!
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77. Questions?
© Fredrik Vraalsen 2012
vraalsen@iterate.no / @fredriv
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78. torsdag 12. september 13