Java 8 Lambda Expressions

Apr 19, 201314 likes12,492 views

Slides for a lightning talk on Java 8 lambda expressions I gave at the Near Infinity (www.nearinfinity.com) 2013 spring conference. The associated sample code is on GitHub at https://github.com/sleberknight/java8-lambda-samples

Mom, why?
Promote immutability
Declare what to do, not how to do it
Easier parallelization & lazy evaluation
Cleaner, more concise code

List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.forEach(new Consumer<Integer>() {
@Override
public void accept(Integer integer) {
System.out.println(integer);
}
});
iterating w/ forEach
(under the hood)

lambda expressions
(argument list) -> code
(final String name, final int age) -> code
(name, age) -> code
name -> code
examples:
type inference
(String name, int age) -> code
}
λ

iterating w/lambdas
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.forEach((final Integer value) -> System.out.println(value));
lambda expression

iterating w/lambdas, type inference
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.forEach(value -> System.out.println(value));

method references
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.forEach(System.out::println);
method reference

transforms using map
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.stream()
.map(value -> value * 2)
.forEach(System.out::println);

filtering
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
numbers.stream()
.filter(value -> value % 2 == 0)
.forEach(System.out::println);

filtering v2
List<String> names = Arrays.asList(
"Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve");
final Function<String, Predicate<String>> startsWithLetter =
letter -> name -> name.startsWith(letter);
names.stream()
.filter(startsWithLetter.apply("J"))
.forEach(System.out::println);

Streams.iterate(1, number -> number + 1)
.map(number -> number * number)
.limit(25)
.forEach(number -> System.out.print(number + " "));
// 1 4 9 16 25 36 49 64 ... 529 576 625
Streams

finding with Optional
List<String> names = Arrays.asList(
"Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve");
Optional<String> firstS = names.stream()
.filter(name -> name.startsWith("S"))
.findFirst();
System.out.println(firstS.orElse("None found"));

reducers
List<String> names = Arrays.asList(
"Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve");
Optional<String> longestName = names.stream()
.reduce((name1, name2) ->
name1.length() >= name2.length() ? name1 : name2);
if (longestName.isPresent()) {
System.out.println(longestName.get());
}

sum reducer
List<Integer> numbers =
Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
long sum = numbers.stream()
.map(value -> value * value)
.sum();

parallelization
numbers.parallelStream()
.filter(number -> isPerfect(number))
.forEach(System.out::println);

http://pragprog.com/book/vsjava8/functional-programming-in-java

http://jdk8.java.net/
JDK 8 Project

sample code available at:
https://github.com/sleberknight/java8-lambda-samples

My Info
scott dot leberknight at nearinfinity dot com
twitter.com/sleberknight www.sleberknight.com/blog
www.nearinfinity.com/blogs/scott_leberknight/all/
scott dot leberknight at gmail dot com

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Java 8 Lambda Expressions

1. Scott Leberknight Java 8 λ Expressions

2. Mom, why? Promote immutability Declare what to do, not how to do it Easier parallelization & lazy evaluation Cleaner, more concise code

3. List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.forEach(new Consumer<Integer>() { @Override public void accept(Integer integer) { System.out.println(integer); } }); iterating w/ forEach (under the hood)

4. lambda expressions (argument list) -> code (final String name, final int age) -> code (name, age) -> code name -> code examples: type inference (String name, int age) -> code } λ

5. iterating w/lambdas List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.forEach((final Integer value) -> System.out.println(value)); lambda expression

6. iterating w/lambdas, type inference List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.forEach(value -> System.out.println(value));

7. method references List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.forEach(System.out::println); method reference

8. transforms using map List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.stream() .map(value -> value * 2) .forEach(System.out::println);

9. filtering List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); numbers.stream() .filter(value -> value % 2 == 0) .forEach(System.out::println);

10. filtering v2 List<String> names = Arrays.asList( "Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve"); final Function<String, Predicate<String>> startsWithLetter = letter -> name -> name.startsWith(letter); names.stream() .filter(startsWithLetter.apply("J")) .forEach(System.out::println);

11. Streams.iterate(1, number -> number + 1) .map(number -> number * number) .limit(25) .forEach(number -> System.out.print(number + " ")); // 1 4 9 16 25 36 49 64 ... 529 576 625 Streams

12. finding with Optional List<String> names = Arrays.asList( "Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve"); Optional<String> firstS = names.stream() .filter(name -> name.startsWith("S")) .findFirst(); System.out.println(firstS.orElse("None found"));

13. reducers List<String> names = Arrays.asList( "Bob", "Tom", "Jeff", "Scott", "Jennifer", "Steve"); Optional<String> longestName = names.stream() .reduce((name1, name2) -> name1.length() >= name2.length() ? name1 : name2); if (longestName.isPresent()) { System.out.println(longestName.get()); }

14. sum reducer List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); long sum = numbers.stream() .map(value -> value * value) .sum();

15. parallelization numbers.parallelStream() .filter(number -> isPerfect(number)) .forEach(System.out::println);

16. how far we went in this short talk...

17. http://pragprog.com/book/vsjava8/functional-programming-in-java

18. http://jdk8.java.net/ JDK 8 Project

19. sample code available at: https://github.com/sleberknight/java8-lambda-samples

20. My Info scott dot leberknight at nearinfinity dot com twitter.com/sleberknight www.sleberknight.com/blog www.nearinfinity.com/blogs/scott_leberknight/all/ scott dot leberknight at gmail dot com

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