Sailing with Java 8 Streams
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The document discusses Java 8 streams and lambda expressions, showcasing their ability to simplify functional programming in Java. It includes examples of how to use streams for data processing and emphasizes the advantages of internal iteration over traditional external iteration methods. The content highlights the efficiency of using parallel streams for performance improvements in computations.
![$ cat limerick.txt | tr -cs "[:alpha:]" "n" | awk '{print
length(), $0}' | sort | uniq
1 a
2 as
2 of
2 on
3 And
3 Who
3 she
3 the
3 was
4 They
4 With
4 face
4 from
4 lady
4 ride
4 rode
5 Niger
5 There
5 smile
5 tiger
5 young
6 inside
6 smiled
8 returned](https://image.slidesharecdn.com/sailingwithjava8streams-160401091838/85/Sailing-with-Java-8-Streams-16-320.jpg)
![public static void main(String []file) throws Exception {
// process each file passed as argument
// try opening the file with FileReader
try (FileReader inputFile = new FileReader(file[0])) {
int ch = 0;
while( (ch = inputFile.read()) != -1) {
// ch is of type int - convert it back to char
System.out.print( (char)ch );
}
}
// try-with-resources will automatically release FileReader object
}
public static void main(String []file) throws Exception {
Files.lines(Paths.get(file[0])).forEach(System.out::println);
}
Existing APIs are enriched with
lambdas and streams support](https://image.slidesharecdn.com/sailingwithjava8streams-160401091838/85/Sailing-with-Java-8-Streams-19-320.jpg)
![interface LambdaFunction {
void call();
}
class FirstLambda {
public static void main(String []args) {
LambdaFunction lambdaFunction = () -> System.out.println("Hello world");
lambdaFunction.call();
}
}
Functional interface - provides
signature for lambda functions
Lambda function/expression
Call to the lambda
Prints “Hello world” on the console when executed](https://image.slidesharecdn.com/sailingwithjava8streams-160401091838/85/Sailing-with-Java-8-Streams-21-320.jpg)
![Method[] objectMethods = Object.class.getMethods();
Stream<Method> objectMethodStream = Arrays.stream(objectMethods);
Stream<String> objectMethodNames
= objectMethodStream.map(method -> method.getName());
Stream<String> uniqueObjectMethodNames = objectMethodNames.distinct();
uniqueObjectMethodNames.forEach(System.out::println);
Arrays.stream(Object.class.getMethods())
.map(method -> method.getName())
.distinct()
.forEach(System.out::println);
Breaking up into separate
(looong) statements for our
understanding](https://image.slidesharecdn.com/sailingwithjava8streams-160401091838/85/Sailing-with-Java-8-Streams-27-320.jpg)
![import java.util.Arrays;
class StringConcatenator {
public static String result = "";
public static void concatStr(String str) {
result = result + " " + str;
}
}
class StringSplitAndConcatenate {
public static void main(String []args) {
String words[] = "the quick brown fox jumps over the lazy dog".split(" ");
Arrays.stream(words).forEach(StringConcatenator::concatStr);
System.out.println(StringConcatenator.result);
}
}
Gives wrong results with
with parallel() call](https://image.slidesharecdn.com/sailingwithjava8streams-160401091838/85/Sailing-with-Java-8-Streams-56-320.jpg)
Sailing with Java 8 Streams
- 1. SAILING WITH JAVA 8 STREAMS ocpjava.wordpress.com Ganesh Samarthyam
- 3. Java 8: Latest (red-hot)
- 6. He he, but lambdas are fun, not scary
- 7. Java meets functional programming (with lambdas)
- 8. Introducing our star feature - lambda functions
- 9. List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = string -> System.out.println(string); strings.forEach(printString); Lambda functions!
- 11. Lambdas is just a fancy name for functions without a name!
- 12. Arrays.asList("eeny", "meeny", "miny", “mo”) .forEach(string -> System.out.println(string)); Internal Iteration List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); for(String string : strings) { System.out.println(string); } External Iteration Lambda expression
- 13. You can use lambdas for some amazing stuff
- 14. sediment pre- carbon ultra-filter post- carbon Filtered water E.g., you can compose lambda functions as in pipes-and-filters
- 15. $ cat limerick.txt There was a young lady of Niger Who smiled as she rode on a tiger. They returned from the ride With the lady inside And a smile on the face of the tiger.
- 16. $ cat limerick.txt | tr -cs "[:alpha:]" "n" | awk '{print length(), $0}' | sort | uniq 1 a 2 as 2 of 2 on 3 And 3 Who 3 she 3 the 3 was 4 They 4 With 4 face 4 from 4 lady 4 ride 4 rode 5 Niger 5 There 5 smile 5 tiger 5 young 6 inside 6 smiled 8 returned
- 17. List<String> lines = Files.readAllLines(Paths.get("./limerick.txt"), Charset.defaultCharset()); Map<Integer, List<String>> wordGroups = lines.stream() .map(line -> line.replaceAll("W", "n").split("n")) .flatMap(Arrays::stream) .sorted() .distinct() .collect(Collectors.groupingBy(String::length)); wordGroups.forEach( (count, words) -> { words.forEach(word -> System.out.printf("%d %s %n", count, word)); }); 1 a 2 as 2 of 2 on 3 And 3 Who 3 she 3 the 3 was 4 They 4 With 4 face 4 from 4 lady 4 ride 4 rode 5 Niger 5 There 5 smile 5 tiger 5 young 6 inside 6 smiled 8 returned
- 18. Lambdas & streams help in productive programming!
- 19. public static void main(String []file) throws Exception { // process each file passed as argument // try opening the file with FileReader try (FileReader inputFile = new FileReader(file[0])) { int ch = 0; while( (ch = inputFile.read()) != -1) { // ch is of type int - convert it back to char System.out.print( (char)ch ); } } // try-with-resources will automatically release FileReader object } public static void main(String []file) throws Exception { Files.lines(Paths.get(file[0])).forEach(System.out::println); } Existing APIs are enriched with lambdas and streams support
- 20. So, lets get our hands dirty and start coding
- 21. interface LambdaFunction { void call(); } class FirstLambda { public static void main(String []args) { LambdaFunction lambdaFunction = () -> System.out.println("Hello world"); lambdaFunction.call(); } } Functional interface - provides signature for lambda functions Lambda function/expression Call to the lambda Prints “Hello world” on the console when executed
- 22. @FunctionalInterface interface LambdaFunction { void call(); } Functional interface Abstract method providing the signature of the lambda function Annotation to explicitly state that it is a functional interface
- 23. arg -> System.out.println(arg) System.out::println Method references - “syntactic sugar” for lambda functions They “route” function parameters
- 24. Java 8 streams (and parallel streams): Excellent example of applying functional programming in practice
- 25. But what are streams?
- 27. Method[] objectMethods = Object.class.getMethods(); Stream<Method> objectMethodStream = Arrays.stream(objectMethods); Stream<String> objectMethodNames = objectMethodStream.map(method -> method.getName()); Stream<String> uniqueObjectMethodNames = objectMethodNames.distinct(); uniqueObjectMethodNames.forEach(System.out::println); Arrays.stream(Object.class.getMethods()) .map(method -> method.getName()) .distinct() .forEach(System.out::println); Breaking up into separate (looong) statements for our understanding
- 30. IntStream.range(1, 6) You can use range or iterate factory methods in the IntStream interface IntStream.iterate(1, i -> i + 1).limit(5)
- 31. 1 2 3 4 5 1 4 9 16 25 map(i -> i * i) IntStream.range(1, 5).map(i -> i * i).forEach(System.out::println); Using streams instead of imperative for i = 1 to 5, print i * i
- 32. Stream.of (1, 2, 3, 4, 5) .map(i -> i * i) .peek(i -> System.out.printf("%d ", i)) .count(); prints: 1 4 9 16 25
- 33. stream can be infinite IntStream.iterate(0, i -> i + 2).forEach(System.out::println); This code creates infinite stream of even numbers!
- 34. IntStream .iterate(0, i -> i + 2) .limit(5) .forEach(System.out::println); Using the “limit” function to limit the stream to 5 integers
- 35. IntStream chars = "bookkeep".chars(); System.out.println(chars.count()); chars.distinct().sorted().forEach(ch -> System.out.printf("%c ", ch)); Cannot “reuse” a stream; this code throws IllegalStateException
- 37. Files.lines(Paths.get("FileRead.java")).forEach(System.out::println); This code prints the contents of the file “FileRead.java” in the current directory
- 38. Pattern.compile(" ").splitAsStream("java 8 streams").forEach(System.out::println); This code splits the input string “java 8 streams” based on whitespace and hence prints the strings “java”, “8”, and “streams” on the console
- 39. new Random().ints().limit(5).forEach(System.out::println); Generates 5 random integers and prints them on the console
- 40. "hello".chars().sorted().forEach(ch -> System.out.printf("%c ", ch)); Extracts characters in the string “hello”, sorts the chars and prints the chars
- 41. Parallel Streams
- 42. race conditions
- 44. deadlocks
- 46. I really really hate concurrency problems
- 48. Sometimes, dreams do come true even at 86 :-)
- 49. So, keep dreaming till you become 86!
- 50. long numOfPrimes = LongStream.rangeClosed(2, 100_000) .filter(PrimeNumbers::isPrime) .count(); System.out.println(numOfPrimes); Prints 9592 2.510 seconds
- 51. Parallel code Serial code Let’s flip the switch by calling parallel() function
- 52. long numOfPrimes = LongStream.rangeClosed(2, 100_000) .parallel() .filter(PrimeNumbers::isPrime) .count(); System.out.println(numOfPrimes); Prints 9592 1.235 seconds
- 53. Wow! That’s an awesome flip switch!
- 54. Internally, parallel streams make use of fork-join framework
- 56. import java.util.Arrays; class StringConcatenator { public static String result = ""; public static void concatStr(String str) { result = result + " " + str; } } class StringSplitAndConcatenate { public static void main(String []args) { String words[] = "the quick brown fox jumps over the lazy dog".split(" "); Arrays.stream(words).forEach(StringConcatenator::concatStr); System.out.println(StringConcatenator.result); } } Gives wrong results with with parallel() call
- 58. ❖ Programming examples are from our book: ❖ Oracle Certified Professional Java SE 8 Programmer Exam 1Z0-809: A Comprehensive OCPJP 8 Certification Guide, S.G. Ganesh, Hari Kiran Kumar, Tushar Sharma, Apress, 2016. ❖ Website: ocpjava.wordpress.com
- 59. Image credits • http://www.wetplanetwhitewater.com/images/uploads/adam_mills_elliott82.jpg • http://s.ecrater.com/stores/321182/53e46c705f68d_321182b.jpg • http://img.viralpatel.net/2014/01/java-lambda-expression.png • https://i.ytimg.com/vi/3C0R_fEXcYA/maxresdefault.jpg • http://farm1.static.flickr.com/74/170765090_53762a686c.jpg • http://www.monazu.com/wp-content/uploads/2012/06/ask-the-right-questions.jpg • https://s-media-cache-ak0.pinimg.com/736x/43/42/8a/43428ac2c352166374d851e895ed5db1.jpg • http://cdn.attackofthecute.com/August-17-2011-12-36-23-peekaboo- kitty-46f32anul-131384-530-410.jpeg • https://ludchurchmyblog.files.wordpress.com/2010/02/myths-legend-pictures-083.jpg • http://www.youramazingplaces.com/wp-content/uploads/2013/06/Mauvoisin-Dam- Switzerland-620x413.jpg • http://www.welikeviral.com/files/2014/08/Image-914.jpg • http://geekandpoke.typepad.com/.a/6a00d8341d3df553ef013485f6be4d970c-800wi • https://qph.fs.quoracdn.net/main-qimg-56547c0506050206b50b80a268bf2a84 • https://i.ytimg.com/vi/kCVsKsgVhBA/maxresdefault.jpg • http://i.livescience.com/images/i/000/022/395/original/man-dreams-bed.jpg • https://static-secure.guim.co.uk/sys-images/Guardian/Pix/pictures/2012/11/26/1353952826063/Alarm- clock-010.jpg
- 60. email [email protected] website www.designsmells.com twitter @GSamarthyam linkedin bit.ly/sgganesh slideshare slideshare.net/sgganesh