Intro to java 8
Download as PPTX, PDF1 like58 views
The document provides an introduction to Java 8 streams. It discusses intermediate and terminal stream operations such as filter(), sorted(), forEach(), and reduce(). It describes reductions like max(), min(), sum(), count(), and average(). It covers find methods, match methods, and Optional. It also discusses limiting, skipping, and distinct elements in streams.
Intro to java 8
- 1. Intro to Java 8 Part 1 - Functional Programming, Lambda and Stream - John Henrique Teixeira de Godoi @john_godoi
- 2. References ● Java 8 Prático - Paulo Silveira, Rodrigo Turini - Casa do Código - 2014 ● Oracle Certified Associate Java SE 8 Programmer I Study Guide - Jeanne Boyarsky, Scott Selikoff - Sybex - 2015 ● Oracle Certified Professional Java SE 8 Programmer II Study Guide - Jeanne Boyarsky, Scott Selikoff - Sybex - 2016 ● Slides from Functional Programming with Scala - Martin Odersky - Coursera
- 3. Brief Review Interfaces, Abstract Classes, Anonymous Classes & Reflection
- 4. Static methods and variables
- 5. Static methods and variables ● What means to be static? ● How do you use static: ○ Methods? ○ Variables? ● Should you use static variables? Why? ○ If it is final is there any difference?
- 7. Abstract Classes ● What is the purpose? ● What is necessary? ○ Can an abstract class not have an abstract method? ○ Can an abstract method not be in an abstract class? ● How many abstract methods can we have?
- 8. Interfaces
- 9. Interfaces ● What is the purpose of an interface in Java? ● Can we have implementation of methods in an interface? Why? ● Can we have variables in an interface? Should we?
- 11. Anonymous Classes ● What is the purpose? ● How do you normally use? ● Is there any rules about its use? Can I use any variable inside? ● Here is most of the lambda’s secret!!!!
- 12. Reflection (No, it ain’t about meditation!)
- 13. Reflection (No, it ain’t about meditation!) ● Ability of the code inspect and change itself. ● It is not a requirement to learn functional programming in Java but it helps!
- 14. Paradigms Object Oriented & Functional
- 15. Object-Oriented Unit: Object/Class ● Encapsulation ● Polymorphism ● Inheritance ● Abstraction ● Objects interact with each other by methods organized in modules
- 16. Functional Programming Unit: function ● Based in the math philosophy ● No mutable variables, no assignments, no imperative control structures ● Focus on function ○ Defined anywhere ○ Function as parameter or return value ○ Operators for functions
- 18. How? ● Object Oriented of course! (Keep that in mind!) ○ Behinds the Java functional features there are interfaces like Function, Consumer, Predicate and Supplier ● JVM can infer the type ○ Received improvements at Java 8 ● “You specify what you want to do rather than dealing with the state of objects. You focus more on expressions than loops.”
- 19. Functional Interfaces ● They contains just one abstract method ○ Any interface with just one abstract method is functional ● You can use any the @FunctionalInterface to check in compile time if the interface attends this requirement
- 23. ƛ ● Lambdas expressions comes to Java 8 to allow functional programming. ● With it is possible: ○ Implement anonymous functions “anywhere” ○ Pass those functions as parameters and return ● It can be used with all sort of functional interfaces lambda
- 24. lambda
- 25. lambda
- 26. Default Methods ● Functional Interface can only have an abstract method.
- 27. Default Methods ● Functional Interface can only have an abstract method. ● What if you want to add an implementation method instead of another abstract one?
- 28. Default Methods ● Functional Interface can only have an abstract method. ● What if you want to add an implementation method instead of another abstract one? ○ WAIT! Interfaces can’t have implementation methods!
- 29. Default Methods ● Functional Interface can only have an abstract method. ● What if you want to add an implementation method instead of another abstract one? ○ WAIT! Interfaces can’t have implementation methods! ■ Right! But just till Java 8! ■ In Java 8 they added the feature called as default method.
- 30. Default Methods ● Functional Interface can only have an abstract method. ● What if you want to add an implementation method instead of another abstract one? ○ WAIT! Interfaces can’t have implementation methods! ■ Right! But just till Java 8! ■ In Java 8 they added the feature called as default method. ● Default methods allows you declare an implementation method in the interface using the modifier default before the method.
- 31. Default Methods
- 32. Default Methods
- 33. Time for a break…
- 35. Methods added ● Some improvements were made to Collection API adding: ○ forEach method to Iterable interface ■ Allows to apply a function (lambda expression for Consumer), by lambda, into all elements
- 36. forEach method
- 37. Methods added ● Some improvements were made to Collection API adding: ○ forEach method to Iterable interface ■ Allows to apply a function (lambda expression for Consumer), by lambda, into all elements ○ removeIf method to Collection interface ■ Remove all the items that matchs to the Predicate
- 38. removeIf method
- 39. Methods added ● Some improvements were made to Collection API adding: ○ forEach method to Iterable interface ■ Allows to apply a function (lambda expression for Consumer), by lambda, into all elements ○ removeIf method to Collection interface ■ Remove all the items that matchs to the Predicate ○ sort method to List interface ■ Sort items in a collection by a lambda expression for Comparator
- 40. sort method
- 41. Methods added ● Some improvements were made to Collection API adding: ○ forEach method to Iterable interface ■ Allows to apply a function (lambda expression for Consumer), by lambda, into all elements ○ removeIf method to Collection interface ■ Remove all the items that matchs to the Predicate ○ sort method to List interface ■ Sort items in a collection by a lambda expression for Comparator ○ replaceAll method to List interface ■ Replace the items by the result of applying a lambda expression for UnaryOperator
- 43. Methods added ● Some improvements were made to Collection API adding: ○ forEach method to Iterable interface ■ Allows to apply a function (lambda expression for Consumer), by lambda, into all elements ○ removeIf method to Collection interface ■ Remove all the items that matchs to the Predicate ○ sort method to List interface ■ Sort items in a collection by a lambda expression for Comparator ○ replaceAll method to List interface ■ Replace the items by the result of applying a lambda expression for UnaryOperator ○ stream and parallelStream methods to Collection interface ■ Those methods are factory methods that create a Stream or a ParallelStream from a Collection
- 44. Streams
- 45. Streams
- 46. Streams ● A functional version of collection ○ Immutable ○ Process data all at once ○ Naturally thread-safe ○ Disposable ○ Fluent API
- 47. Streams
- 48. To be continued... Avaliação: https://goo.gl/forms/DJYEDDbUhecRbZul2
- 49. Intro to Java 8 Part 2 - More Stream - John Henrique Teixeira de Godoi jgodoi@fitec.org.br @john_godoi
- 52. Lambda & Default Methods
- 54. Now More Stream!
- 55. Streams ● Operations at a stream can be: ○ Intermediate ■ Can be more than one in a pipeline ■ Return type is a stream type ■ Stream still valid after call ■ Lazy execution ■ Ex.: filter(), sorted(), map()
- 56. Streams ● Operations at a stream can be: ○ Intermediate ■ Can exist multiple time in a pipeline ■ Return type is a stream type ■ Stream still valid after call ■ Lazy execution ■ Ex.: filter(), sorted(), map() ○ Terminal ■ Required part of a useful pipeline ■ Executed upon method call ■ Ex.: forEach()
- 57. Streams ● forEach lyric.stream().forEach(line -> System.out.println(line)); ● filter lyric.stream().filter(line -> !line.isEmpty()).forEach(line -> System.out.println(line)); ● sort lyric.stream().map(line -> line.toUpperCase()).forEach(line -> System.out.println(line)); ● map lyric.stream().sorted().forEach(line -> System.out.println(line)); lyric.stream().sorted(Comparator.reverseOrder()).forEach(line -> System.out.println(line));
- 58. The creation of Java 1. The JVM was without types and there was just void. So, Gosling came and said let there be primitives. Then appeared int, long, char, float, double and others.
- 59. The creation of Java 1. The JVM was without types and there was just void. So, Gosling came and said let there be primitives. Then appeared int, long, char, float, double and others. 2. From the declarative chaos Gosling made the Object. It would domain everything in the JVM. Gosling seeing the Object alone and without definition, he decide to create the Class. From their union others objects could be instantiated and defined to populate the memory. And Gosling saw that was good.
- 60. The creation of Java 1. The JVM was without types and there was just void. So, Gosling came and said let there be primitives. Then appeared int, long, char, float, double and others. 2. From the declarative chaos Gosling made the Object. It would domain everything in the JVM. Gosling seeing the Object alone and without definition, he decide to create the Class. From their union others objects could be instantiated and defined to populate the memory. And Gosling saw that was good. 3. Then Gosling created also classes for the primitives (Integer, Long, Character, Float, Double and others), so them could instantiate objects too. To those classes, he called them as Wrappers. A primitive could turn into a object of its Wrapper automatically, and vice-versa. That came to be known as autoboxing.
- 61. autoboxing
- 62. Wickedness in the Runtime 1. The objects began to increase in number. And autoboxing was being used all the time. So, things started to make the runtime out of control and slow.
- 63. Wickedness in the Runtime 1. The objects began to increase in number. And autoboxing was being used all the time. So, things started to make the runtime out of control and slow. 2. One prophet of Gosling, Bloch, with the Effective book proclaimed that, because of the time consuming in massive processing, autoboxing should be avoided always as possible.
- 64. Wickedness in the Runtime 1. The objects began to increase in number. And autoboxing was being used all the time. So, things started to make the runtime out of control and slow. 2. One prophet of Gosling, Bloch, with the Effective book proclaimed that, because of the time consuming in massive processing, autoboxing should be avoided always as possible. 3. Collection API is based in Objects and doesn’t support primitives.
- 65. Wickedness in the Runtime 1. The objects began to increase in number. And autoboxing was being used all the time. So, things started to make the runtime out of control and slow. 2. One prophet of Gosling, Bloch, with the Effective book proclaimed that, because of the time consuming in massive processing, autoboxing should be avoided always as possible. 3. Collection API is based in Objects and doesn’t support primitives. And now… Who could help us?
- 66. IntStream and the Stream Family
- 67. mapToInt ● Using map function to create a stream of integers probably: Stream<Integer> integerStream = units.stream().map(unit -> unit.getConsume()); ● That uses autoboxing and has potential to become a time consuming problem. One way to avoid it, is using the mapToInt version. IntStream intStream = units.stream().mapToInt(unit -> unit.getConsume());
- 68. Another way to look at streams ● The sintaxe of Stream API looks like SQL queries. ● And its concept as well.
- 69. reductions ● Reductions are terminal operations that reduces ALL the data to one just one value result ● This result can be Optional
- 70. reductions ● max OptionalInt max = units.stream().mapToInt(unit -> unit.getAttack()).max(); ● min OptionalInt min = units.stream().mapToInt(unit -> unit.getAttack()).min();
- 71. reductions ● sum int sum = units.stream().mapToInt(unit -> unit.getAttack()).sum(); ● count long count = units.stream().count(); ● average OptionalDouble average = units.stream().mapToInt(unit -> unit.getAttack()).average();
- 72. reductions ● reduce int totalAttack = units.stream().mapToInt(unit -> unit.getAttack()).reduce(0, (combined, attack) -> combined + attack); Integer alsoTotalAttack = units.stream().reduce(0, (result, unit) -> result + unit.getAttack(), (combined, actual) -> combined + actual);
- 73. summaryStatistics ● This class will give you some statistics about your numeric stream IntSummaryStatistics summaryStatistics = units.stream().mapToInt(unit -> unit.getAttack()).summaryStatistics(); System.out.println(summaryStatistics); // IntSummaryStatistics{count=25, sum=150, min=2, average=6,000000, max=10}
- 74. find methods ● The find methods returns an element with the stream is not empty. But if the stream is empty, it return an Optional value.
- 75. find methods ● The find methods returns an element with the stream is not empty. But if the stream is empty, it return an Optional value. ● findFirst() - return the “real” first element on the list Optional<Unit> firstPeon = units.stream().filter(u -> u instanceof Peon).findFirst();
- 76. find methods ● The find methods returns an element with the stream is not empty. But if the stream is empty, it return an Optional value. ● findFirst() - return the “real” first element on the list Optional<Unit> firstPeon = units.stream().filter(u -> u instanceof Peon).findFirst(); ● findAny() - return the first element on the list Optional<Unit> anyAlive = units.parallelStream().filter(u -> u.getEnergy() > 0).findAny();
- 77. matchs ● The match methods analyse the stream data and tell whether a predicate is valid or not
- 78. matchs ● allMatch() - looks through ALL the data whether them match to the predicate boolean allMatch = units.stream().allMatch(unit -> unit instanceof Unit);
- 79. matchs ● allMatch() - looks through ALL the data whether them match to the predicate boolean allMatch = units.stream().allMatch(unit -> unit instanceof Unit); ● anyMatch() - looks through the data whether any match to the predicate, if positive return the first to match and stops processing boolean anyMatch = units.stream().anyMatch(unit -> unit instanceof Healer);
- 80. matchs ● allMatch() - looks through ALL the data whether them match to the predicate boolean allMatch = units.stream().allMatch(unit -> unit instanceof Unit); ● anyMatch() - looks through the data whether any match to the predicate, if positive return the first to match and stops processing boolean anyMatch = units.stream().anyMatch(unit -> unit instanceof Healer); ● noneMatch() - looks through ALL the data checking if none of them match to the predicate boolean noneMatch = units.stream().noneMatch(unit -> unit instanceof Hero);
- 81. Optional ● Some operations can have an unexpected result or no result at all.
- 82. Optional ● Some operations can have an unexpected result or no result at all. ● You could use null to those cases but it comes with more problems than solutions.
- 83. Optional ● Some operations can have an unexpected result or no result at all. ● You could use null to those cases but it comes with more problems than solutions. ● In those case, you may also want a default value or an object that helps to determine that those cases occurred.
- 84. Optional ● Some operations can have an unexpected result or no result at all. ● You could use null to those cases but it comes with more problems than solutions. ● In those case, you may also want a default value or an object that helps to determine that those cases occurred. ● So since Java 8, “If you want Optional, you got it!”
- 85. Optional ● Some operations can have an unexpected result or no result at all. ● You could use null to those cases but it comes with more problems than solutions. ● In those case, you may also want a default value or an object that helps to determine that those cases occurred. ● So since Java 8, “If you want Optional, you got it!” ● And it comes in others flavors: OptionalInt, OptionalLong e OptionalDouble
- 86. Optional ● Optional class offers:
- 87. Optional
- 88. Time for a break…
- 89. Limit, skip, distinct ● The limit() and skip() makes a Stream smaller ○ skip returns a stream without the first elements, the quantity is specified by parameter Stream<Unit> saveTheFirstThree = units.stream().skip(10);
- 90. Limit, skip, distinct ● The limit() and skip() makes a Stream smaller ○ skip returns a stream without the first elements, the quantity is specified by parameter Stream<Unit> saveTheFirstThree = units.stream().skip(10); ○ limit returns just a stream with the first elements, the quantity is specified by parameter saveTheFirstThree.limit(5).forEach(unit -> System.out.println(unit));
- 91. Limit, skip, distinct ● The limit() and skip() makes a Stream smaller ○ skip returns a stream without the first elements, the quantity is specified by parameter Stream<Unit> saveTheFirstThree = units.stream().skip(10); ○ limit returns just a stream with the first elements, the quantity is specified by parameter saveTheFirstThree.limit(5).forEach(unit -> System.out.println(unit)); ● The distinct method removes all the duplicates units.stream().map(unit -> unit.getClass().getSimpleName()).distinct().forEach(name -> System.out.println(name));
- 92. Reference Method ● Let’s say that is just another way to create a lambda
- 93. Reference Method ● Let’s say that is just another way to create a lambda ● When you want to create a lambda with just one call to a method, you could just use a reference for this method
- 94. Reference Method ● Let’s say that is just another way to create a lambda ● When you want to create a lambda with just one call to a method, you could just use a reference for this method ● Calling a method from each instance double averageSpeed = units.stream().mapToInt(Unit::getSpeed).average().getAsDouble(); ● Receiving each instance as argument units.stream().forEach(System.out::println);
- 95. Collectors ● Can we obtain a collection back from a stream? ● Yes, we can!
- 96. Collectors ● Can we obtain a collection back from a stream? ● Yes, we can! ● At stream there are a method called collect() it receives a implementation for Collector, that will tell how to create the collection, and return the collection with the elements of the stream inside.
- 97. Collectors ● Can we obtain a collection back from a stream? ● Yes, we can! ● At stream there are a method called collect() it receives a implementation for Collector, that will tell how to create the collection, and return the collection with the elements of the stream inside. ● Also, there is a Collectors class that wraps those implementations. ○ You can passa just a call for one of its methods to collect() units.stream().filter(unit -> unit.getAttack() > 0).collect(Collectors.toList());
- 98. Grouping ● Sometimes you may want to classify the elements of a stream by some features ● For that you could make groups of them by values of the selected features ● groupingBy a feature will result in a map Map<String, List<Unit>> unitsByType = units.stream().collect(Collectors.groupingBy(unit -> unit.getClass().getSimpleName()));
- 99. Partitioning ● groupingBy a boolean feature has a specific method partitioningBy Map<Boolean, List<Unit>> strongers = units.stream().collect(Collectors.partitioningBy(unit -> unit.getAttack() >= 10)); System.out.println(strongers.get(true)); System.out.println(strongers.get(false));
- 100. Comparator ● Since 8th version of Java, the Comparator interface is functional. units.sort(Comparator.comparing(Unit::getAttack)); ● Beyond that some default methods were added to this interface with some commons uses. These methods can be called chaining the calls. units.sort(Comparator.comparing(Unit::getAttack).thenComparing(unit -> unit.getClass().getSimpleName()));
- 102. What we have done? ● Reviews of Java SE ● Functional Programming ● Functional Interfaces ● Default Methods ● lambda ● Streams till exhaustion (Still have more to cover!) ● Optional ● Reference Method ● Collectors ● Comparators
- 103. Challenge #1 ● Create an abstract class called Creator ● Creator will have a static method create that receives any Class that implements an interface Creature and return an instance of it ● The create implementation should go inside an Thread
- 104. Challenge #2 ● Create an interface Tekpix with ○ A default method startComercial that will return a greeting message ○ An abstract method whatItDoes
- 105. Challenge #3 plantsAndWeeds = Arrays.asList("Camellias 7", "weed 5", "Sunflower 3", "Lily 1", "weed 4", "Azalea 5", "weed 2", "Begonia 4"); ● Remove all the weeds ● Increment the number after their names by 1 ● Sort by the number at the end in decrescent order ● Print them without the numbers
- 106. Challenge #4 ● Convert challenge #3 to stream
- 107. Challenge #5 ● Who wants to be a millionaire? ● Figure out the statistics of Bitcoin price dataset
- 108. Challenge #6 ● From celebrities_profile.txt ○ Find the top 10 with more followers ○ Group them by gender ○ Sort by created_at
- 109. Bonus Challenge ● Try to solve our Java challenge at: https://bitbucket.org/dev- fitec/desafiojavafitec
- 110. Intro to Java 8 Part 2 - More Stream - John Henrique Teixeira de Godoi jgodoi@fitec.org.br @john_godoi