Functional Programming in Java 8 - Exploiting Lambdas
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This document introduces lambda functions and functional programming in Java 8. It defines lambda functions as anonymous functions without a name. Functional programming views programs as functions that accept inputs and produce outputs. Lambda functions and streams help enable a more functional approach to programming in Java. Parallel streams can improve performance by processing elements concurrently.
![$ 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/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-20-320.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/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-23-320.jpg)
![Java 8 is the new Groovy ;-)
import java.io.*;
class Type {
public sta7c void main(String []files) {
// process each file passed as argument
for(String file : files) {
// try opening the file with FileReader
try (FileReader inputFile = new FileReader(file)) {
int ch = 0;
while( (ch = inputFile.read()) != -1) {
// ch is of type int - convert it back to char
System.out.print( (char)ch );
}
} catch (FileNotFoundExcep7on fnfe) {
System.err.prinR("Cannot open the given file %s ", file);
}
catch(IOExcep7on ioe) {
System.err.prinR("Error when processing file %s; skipping it", file);
}
// try-with-resources will automa7cally release FileReader object
}
}
}
args.each { println new File(it).getText() }](https://image.slidesharecdn.com/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-24-320.jpg)
![Java 8 lambdas - “Hello world!”
interface LambdaFunction {
void call();
}
class FirstLambda {
public static void main(String []args) {
LambdaFunction lambdaFunction = () -> System.out.println("Hello world");
lambdaFunction.call();
}
}](https://image.slidesharecdn.com/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-26-320.jpg)
![Java 8 lambdas - “Hello world!”
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/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-27-320.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/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-39-320.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/functionalprogramminginjava8-exploitinglambdas-160623040016/85/Functional-Programming-in-Java-8-Exploiting-Lambdas-65-320.jpg)
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Functional Programming in Java 8 - Exploiting Lambdas
- 1. Functional Programming in Java 8 Lambda Functions GANESH & HARI CODEOPS TECHNOLOGIES [email protected] [email protected]
- 4. Java meets functional programming (with lambdas)
- 5. Java is not your grandma’s language anymore!
- 7. He he, but lambdas are fun, not scary
- 8. List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = string -> System.out.println(string); strings.forEach(printString); Lambda functions!
- 10. Lambdas is just a fancy name for functions without a name!
- 11. What are lambda functions? ❖ (Java 8) One way to think about lambdas is “anonymous function” or “unnamed function” - they are functions without a name and are not associated with any class ❖ They don’t change external state
- 12. What is functional programming? ❖ Functional languages view programs as an entity— called a function—that accepts inputs and produces output ❖ Functions are connected together by their outputs to other functions’ inputs ❖ Underlying approach: “Evaluate an expression. Then use the results for something else.”
- 13. Perspective - for loops! List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); for(String string : strings) { System.out.println(string); } External Iteration
- 14. Perspective - for loops! List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); strings.forEach(string -> System.out.println(string)); Internal Iteration
- 15. Perspective - for loops! List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); strings.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
- 16. Perspective - for loops! List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); strings.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 Procedural thinking Functional thinking
- 17. You can use lambdas for some amazing stuff
- 18. sedime nt pre- carbon ultra- filter post- carbon Filtered water E.g., you can compose lambda functions as in pipes-and-filters
- 19. $ 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.
- 20. $ 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
- 21. 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
- 22. Lambdas & streams help in productive programming!
- 23. 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
- 24. Java 8 is the new Groovy ;-) import java.io.*; class Type { public sta7c void main(String []files) { // process each file passed as argument for(String file : files) { // try opening the file with FileReader try (FileReader inputFile = new FileReader(file)) { int ch = 0; while( (ch = inputFile.read()) != -1) { // ch is of type int - convert it back to char System.out.print( (char)ch ); } } catch (FileNotFoundExcep7on fnfe) { System.err.prinR("Cannot open the given file %s ", file); } catch(IOExcep7on ioe) { System.err.prinR("Error when processing file %s; skipping it", file); } // try-with-resources will automa7cally release FileReader object } } } args.each { println new File(it).getText() }
- 25. Lambdas in Java 8
- 26. Java 8 lambdas - “Hello world!” interface LambdaFunction { void call(); } class FirstLambda { public static void main(String []args) { LambdaFunction lambdaFunction = () -> System.out.println("Hello world"); lambdaFunction.call(); } }
- 27. Java 8 lambdas - “Hello world!” 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
- 28. Parts of a lambda expression () -> System.out.println("Hello world"); No parameters, i.e., () Arrow operator that separates parameters and the body The lambda body Return type “void” inferred from the body
- 29. Functional interfaces @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
- 30. Using built-in functional interfaces // within Iterable interface default void forEach(Consumer<? super T> action) { Objects.requireNonNull(action); for (T t : this) { action.accept(t); } } // in java.util.function package @FunctionalInterface public interface Consumer<T> { void accept(T t); // the default andThen method elided }
- 31. Using built-in functional interfaces List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = string -> System.out.println(string); strings.forEach(printString); List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); strings.forEach(string -> System.out.println(string));
- 32. Method references Method references - “syntactic sugar” for lambda functions They “route” function parameters arg -> System.out.println(arg) System.out::println
- 33. Method references List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = System.out::println; strings.forEach(printString); Method reference List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = string -> System.out.println(string); strings.forEach(printString);
- 34. Method references Cannot use method references when lambda functions do more than“routing” function parameters strings.forEach(string -> System.out.println(string.toUpperCase())); More processing here than just “routing” parameters
- 35. Method references List<String> strings = Arrays.asList("eeny", "meeny", "miny", "mo"); Consumer<String> printString = System.out::println; strings.forEach(printString); public static void printUpperCaseString(String string) { System.out.println(string.toUpperCase()); } strings.forEach(MethodReference::printUpperCaseString);
- 36. Java 8 streams (and parallel streams): Excellent example of applying functional programming in practice
- 37. But what are streams?
- 39. 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
- 42. IntStream.range(1, 6) You can use range or iterate factory methods in the IntStream interface IntStream.iterate(1, i -> i + 1).limit(5)
- 43. 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
- 44. 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
- 45. stream can be infinite IntStream.iterate(0, i -> i + 2).forEach(System.out::println); This code creates infinite stream of even numbers!
- 46. IntStream .iterate(0, i -> i + 2) .limit(5) .forEach(System.out::println); Using the “limit” function to limit the stream to 5 integers
- 47. 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
- 48. Files.lines(Paths.get("FileRead.java")).forEach(System.out::println); This code prints the contents of the file “FileRead.java” in the current directory
- 49. 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
- 50. new Random().ints().limit(5).forEach(System.out::println); Generates 5 random integers and prints them on the console
- 51. "hello".chars().sorted().forEach(ch -> System.out.printf("%c ", ch)); Extracts characters in the string “hello”, sorts the chars and prints the chars
- 52. Parallel Streams
- 53. race conditions
- 55. deadlocks
- 57. I really really hate concurrency problems
- 59. long numOfPrimes = LongStream.rangeClosed(2, 100_000) .filter(PrimeNumbers::isPrime) .count(); System.out.println(numOfPrimes); Prints 9592 2.510 seconds
- 60. Parallel code Serial code Let’s flip the switch by calling parallel() function
- 61. long numOfPrimes = LongStream.rangeClosed(2, 100_000) .parallel() .filter(PrimeNumbers::isPrime) .count(); System.out.println(numOfPrimes); Prints 9592 1.235 seconds
- 62. Wow! That’s an awesome flip switch!
- 63. Internally, parallel streams make use of fork-join framework
- 65. 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
- 68. Upcoming bootcamps/workshops Modern Software Architecture - July 2 Modern Programming with Java 8 - July 16 Software Refactoring in Practice - July 23
- 69. Image credits ❖ http://mayhemandmuse.com/wp-content/uploads/2013/04/This-optical-illusion-drawing-by-WE- Hill-shows-both-his-wife-and-his-mother-in-law.jpg ❖ http://www.webtrafficroi.com/wp-content/uploads/2012/10/mahatma-gandhi-apple-think- different.jpg ❖ http://rexx-language-association-forum.44760.x6.nabble.com/file/n2236/Ruby-lambda-function.jpg ❖ http://www.ibm.com/developerworks/library/j-jn16/figure1.png ❖ http://www.ibm.com/developerworks/library/j-jn16/figure2.png ❖ http://img.viralpatel.net/2014/01/java-lambda-expression.png ❖ http://www.codercaste.com/wp-content/uploads/2011/01/animals.png ❖ http://blog.takipi.com/wp-content/uploads/2014/03/blog_lambada_2.png ❖ http://quotespictures.com/wp-content/uploads/2014/01/it-is-not-the-strongest-of-the-species-that- survive-nor-the-most-intelligent-but-the-one-most-responsive-to-change-charles-darwin.jpg ❖ http://7-themes.com/data_images/out/27/6859733-surfing-wallpaper.jpg
- 70. [email protected] @GSamarthyam www.codeops.tech slideshare.net/sgganesh +91 98801 64463 bit.ly/sgganesh