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Lambda and Stream Master class - part 1
The document outlines the agenda and content of a Java Lambda Stream master class, focusing on API design, functional interfaces, and streams with practical exercises. It includes examples of consumers, predicates, and comparators, as well as implementing functional programming concepts. Additionally, resources such as GitHub links and further class details are provided.
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Lambda and Stream Master class - part 1
- 1. #Devoxx Java Lambda Stream MasterClass – Part 1 @StuartMarks @JosePaumard
- 2. #LambdaHOL#Devoxx Master Class? Did youbring your laptop?
- 3. #LambdaHOL#Devoxx Yes you did! Whatabout: - 10-15mn of explaination - 3-5mn of time to solve the exercice - ~5mn to show a solution
- 4. #LambdaHOL#Devoxx No you didn’t! Whatabout: - 10-15mn of explaination - 3-5mn to show a first example - 3-5mn to show a second example
- 5. #LambdaHOL#Devoxx The LambdaHOL 8 testclasses, with 80 exercises to complete - Lambda, functionnal interfaces - Comparators - Streams, Collectors - Some challenges at the end - Updated regularly With solutions!
- 6. #LambdaHOL#Devoxx The LambdaHOL You canfind it here https://github.com/stuart-marks/LambdaHOLv2
- 7. #LambdaHOL#Devoxx Agenda 1st part: APIDesign with lambdas and Functional interfaces 2nd part: Streams, reductions, collectors
- 8. #LambdaHOL#Devoxx API Design withlambdas Chaining lambdas with default methods - Consumer interface - Predicate interface Composing lambdas - Comparator interface Partial Application - Currency converter example
- 9. #LambdaHOL#Devoxx Stuart Marks JDK CoreLibraries Developer Java Plaform Group, Oracle Twitter: @stuartmarks
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- 12. #LambdaHOL#Devoxx For today The startingpoint is here: https://github.com/JosePaumard/lambda-master-class-part1
- 13. #Devoxx #LambdaHOL A FewWords on Functional Interfaces
- 14. #LambdaHOL#Devoxx Functional interfaces A functionalinterface is: ▪ An interface ▪ With one abstract method ▪ Methods from Object do not count ▪ May be annotated with @FunctionalInterface
- 15. #LambdaHOL#Devoxx Functional interfaces A functionalinterface can be implemented with a lambda! Comparator<String> comparator = new Comparator<String>() { public int compareTo(String s1, String s2) { return Integer.compare(s1.length(), s2.length()) ; } } Comparator<String> comparator = (String s1, String s2) -> Integer.compare(s1.length(), s2.length()) ;
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- 17. #LambdaHOL#Devoxx 1st example A consumerthat clears a string builder @Test public void consumer_1() { Consumer<List<String>> consumer = null; // TODO List<String> list = new ArrayList<>(Arrays.asList("a", "b", "c")); consumer.accept(list); assertThat(list).isEmpty(); }
- 18. #LambdaHOL#Devoxx 2nd example A consumerthat calls two Consumers @Test public void consumer_2() { Consumer<List<String>> c1 = list -> list.add("first"); Consumer<List<String>> c2 = list -> list.add("second"); Consumer<List<String>> consumer; // TODO List<String> list = new ArrayList<>(Arrays.asList("a", "b", "c")); consumer.accept(list); assertThat(list).containsExactly("a", "b", "c", "first", "second"); }
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- 20. #LambdaHOL#Devoxx 1st example A predicatethat negates another predicate @Test public void predicate_1() { Predicate<String> predicate = s -> s.isEmpty(); Predicate<String> notPredicate; // TODO assertThat(notPredicate.test("")).isFalse(); assertThat(notPredicate.test("Not empty!")).isTrue(); }
- 21. #LambdaHOL#Devoxx 2nd example A predicatethat is true if a string is non null and non empty @Test public void predicate_2() { Predicate<String> p1 = s -> s != null; Predicate<String> p2 = s -> s.isEmpty(); Predicate<String> p3; // TODO assertThat(p3.test("")).isFalse(); assertThat(p3.test(null)).isFalse(); assertThat(p3.test("Not empty!")).isTrue(); }
- 22. #LambdaHOL#Devoxx 3rd example How todesign a xOr() method on Predicate? @Test public void predicate_3() { Predicate<String> p1 = s -> s.length() == 4; Predicate<String> p2 = s -> s.startsWith("J"); Predicate<String> p3; // TODO assertThat(p3.test("True")).isTrue(); assertThat(p3.test("Julia")).isTrue(); assertThat(p3.test("Java")).isFalse(); }
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- 24. #LambdaHOL#Devoxx A first example Whatis this code doing? Comparator<Person> cmp = new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { return p1.getLastName().compareTo(p2.getLastName()); } };
- 25. #LambdaHOL#Devoxx A first example Whatis this code doing? Comparator<Person> cmp = new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { int cmp = p1.getLastName().compareTo(p2.getLastName()); if (cmp == 0) { return p1.getFirstName().compareTo(p2.getFirstName()); } else { return cmp; } } };
- 26. #LambdaHOL#Devoxx A first example Whatis this code doing?Comparator<Person> cmp = new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { int cmp = p1.getLastName().compareTo(p2.getLastName()); if (cmp == 0) { cmp = p1.getFirstName().compareTo(p2.getLastName()); if (cmp == 0) { return Integer.compare(p1.getAge(), p2.getAge()); } else { return cmp; } } else { return cmp; } } };
- 27. #LambdaHOL#Devoxx A first example Whatis this code doing?Comparator<Person> cmp = new Comparator<Person>() { @Override public int compare(Person p1, Person p2) { int cmp = p1.getLastName().compareTo(p2.getLastName()); if (cmp == 0) { cmp = p1.getFirstName().compareTo(p2.getFirstName()); if (cmp == 0) { return Integer.compare(p1.getAge(), p2.getAge()); } else { return cmp; } } else { return cmp; } } };
- 28. #LambdaHOL#Devoxx A first example Whatis this code doing? Comparator<Person> cmp = Comparator.comparing(Person::getLastName) .thenComparing(Person::getFirstName) .thenComparing(Person::getAge);
- 29. #LambdaHOL#Devoxx 1st example A comparatorthat puts null values at the end Person michael = new Person("Michael", "Jackson", 51); Person rod = new Person("Rod", "Stewart", 71); Person paul = new Person("Paul", "McCartney", 74); Person mick = new Person("Mick", "Jagger", 73); Person jermaine = new Person("Jermaine", "Jackson", 61); @Test public void comparator_1() { Comparator<Person> cmp = null; // TODO assertThat(cmp.compare(michael, rod)).isLessThan(0); assertThat(cmp.compare(paul, paul)).isEqualTo(0); assertThat(cmp.compare(michael, jermaine)).isGreaterThan(0); assertThat(cmp.compare(mick, null)).isLessThan(0); assertThat(cmp.compare(null, mick)).isGreaterThan(0); }
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- 31. #LambdaHOL#Devoxx A Currency Converter Giventhe following data… Date=2018/11/05 EUR=1 AUD=1.58125 BRL=4.20735 NOK=9.51682 GBP=0.87749 PLN=4.30044 CAD=1.49181 RUB=75.25596
- 32. #LambdaHOL#Devoxx A Currency Converter …write the following currency converter: LocalDate date = ...; CurrencyConverter plnToAud = CurrencyConverter.of(date) .from("PLN") .to("AUD"); float pln = ...; float aud = plnToAud.convert(pln);
- 33. #LambdaHOL#Devoxx A Validator Given thefollowing bean public class Person { private String lastName ; private int age ; // getters, setters, constructeurs }
- 34. #LambdaHOL#Devoxx A Validator Implement thefollowing pattern If the user is not valid: get() throws an exception, with all the exceptions of each validator in the suppressed exceptions Validator<Person> validator = Validator. .firstValidate(p -> p.getName() == null, "name is null") .thenValidate(p -> p.getAge() < 0, "age is negative") .thenValidate(p -> p.getAge() > 150, "age is greater than 150"); person = validator.validate(person).get();
- 35. #LambdaHOL#Devoxx A Validator If theuser is not valid: get() throws an exception, with all the exceptions of each validator in the suppressed exceptions Validator<Person> validator = Validator .firstValidate(p -> p.getName() == null, "name is null") .thenValidate(p -> p.getAge() < 0, "age is negative") .thenValidate(p -> p.getAge() > 150, "age is greater than 150"); person = validator.validate(person).get();
- 36. #Devoxx Don’t miss the2nd day: 1) More functional programming! 2) Stream, reduction 3) Collectors Day break!
- 37. #Devoxx Java Lambda Stream MasterClass – Part 2 @StuartMarks @JosePaumard
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- 40. #Devoxx Come back forthe last part! 1) Collectors 2) Challenges Coffee break!
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