Java8 and Functional Programming
Download as PPTX, PDF1 like384 views
This document discusses new features in Java 8 including lambda expressions, default methods, streams, optionals, and date/time API improvements. It provides examples of using lambda expressions and streams to more concisely represent and process collections of data in a functional way. The document also discusses optionals as a way to safely handle potential null values without exceptions.
![Groovy Closure
def myConst = 5
def incByConst = { num -> num + myConst }
println incByConst(10) //==>15
myConst = 20
println incByConst(10) //==>30
def result=[]
(1..10).collect(result,{a->a*a})
result==[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]](https://image.slidesharecdn.com/java8-150724022512-lva1-app6891/85/Java8-and-Functional-Programming-5-320.jpg)
![Optionals
❖ how to model “absence of a value”
❖ Scala introduced Option[T]
❖ Java 8 call it Optional[T]
❖ Optional<String> version =
optcomputer.map(Computer::getSoundcard).map(Sound
Card::getUSB).map(USB::getVersion)](https://image.slidesharecdn.com/java8-150724022512-lva1-app6891/85/Java8-and-Functional-Programming-20-320.jpg)
Java8 and Functional Programming
- 2. What has been happening in Computer ❖ Moor’s Law no longer applicable ❖ Computer speed is not increasing unlimited ❖ MultiCore Computer ❖ Pre-Java8 does not take advantage of multicore computer Power ❖ Threading is hard, multicore make it harder
- 3. Computer Languages ❖ Groovy, Scala, Clojure, Kotlin, JavaScript/CoffeeScript, Go, Swift, Lua, ErLang, Haskell, Ruby,C#,F#,… ❖ Closure ❖ Lambda Expression ❖ Pre-Java8 Did not have this, so what?
- 4. What is Closure “In computer science, a closure is a first-class function with free variables that are bound in the lexical environment.”
- 5. Groovy Closure def myConst = 5 def incByConst = { num -> num + myConst } println incByConst(10) //==>15 myConst = 20 println incByConst(10) //==>30 def result=[] (1..10).collect(result,{a->a*a}) result==[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
- 6. What is Lambda Expression ❖ A concise representation of an anonymous function that can be passed around: ❖ doesn't have a name, but has ❖ a list of parameters ❖ a body ❖ a return type ❖ possibly a list of exceptions
- 7. Example Lambda Expression //Anonymous version Runnable r1 = new Runnable(){ @Override public void run(){ System.out.println("Hello world one!"); } }; // Lambda Runnable Runnable r2 = () -> System.out.println("Hello world two!"); // Run em! r1.run(); r2.run(); Compare the one-liner lambda with the 4+ lines legacy code!
- 8. What’s new in Java8 ❖ Lambda expression ❖ Default methods ❖ Stream ❖ optionals ❖ Date/Time API
- 9. What Lambda Expression brings? ❖ Pass code concisely-functions are passed as values ❖ Collection: ❖ List<Person> pl ;//Given a list of Persons ❖ looping: pl.forEach( p -> p.printName() ); ❖ filtering and chaining: ❖ pl.stream().filter(p->p.getAge()>30).sort(comparing((a)- >a.getAge())).forEach(Person::printName); ❖ This one line replaces 20 lines of traditional code and does more (later on stream)
- 10. functional interfaces ❖ functional interface specifies exactly one abstract method ❖ Examples: ❖ Predicate<T>:boolean test(T t) ❖ Comparator<T>:compare(T o1, T o2)
- 12. Default Methods ❖ Interface can contain method signatures for which an implementation class doesn’t have to provide implementation ❖ interface can now provide default method implementation
- 13. Streams ❖ Manipulate collection of data in a declarative way. ❖ Streams can be processed in parallel transparently without having to write any multithreaded code!
- 14. Stream example ❖ pl.stream().filter(p->p.getAge()>30).sort(comparing((a)- >a.getAge()).reversed().thenComparing(Person::getHeigh t())).map(Person::getName()).collect(toList)) ❖ To Exploit multicore architecture and execute the code in parallel ❖ pl.parallelStream().filter(p- >p.getAge()>30).sort(comparing((a)- >a.getAge()).reversed().thenComparing(Person::getHeigh t())).map(Person::getName()).collect(toList))
- 15. Hi Map Collect/Reduce ❖ pl.parallelStream().filter(p- >p.getAge()>30).sort(comparing((a)- >a.getAge()).reversed().thenComparing(Person::getHei ght())).map(Person::getName()).collect(toList)) ❖ pl.parallelStream().filter(p- >p.getAge()>30).sort(comparing((a)- >a.getAge()).reversed().thenComparing(Person::getHei ght())).map(Person::getSallary()).reduce(Integer::sum)).get ()
- 16. Optionals ❖ String version = computer.getSoundcard().getUSB().getVersion(); ❖ Problem: Multiple NPE possible. Traditional way: String version = "UNKNOWN"; if(computer != null){ Soundcard soundcard = computer.getSoundcard(); if(soundcard != null){ USB usb = soundcard.getUSB(); if(usb != null){ version = usb.getVersion(); } } }
- 17. Optionals ❖ The problem with Null ❖ source of error: NPE ❖ bloats code ❖ meaningless ❖ break java philosophy ❖ a hole in type system
- 18. –Tony Hoare Introducing Null reference in ALGOL W in 1965 was “my billion-dollar mistake”
- 19. Optionals ❖ Groovy safe navigation operator+Elvis operator ❖ String version = computer?.soundcard?.uSB.version ?: "UNKNOWN";
- 20. Optionals ❖ how to model “absence of a value” ❖ Scala introduced Option[T] ❖ Java 8 call it Optional[T] ❖ Optional<String> version = optcomputer.map(Computer::getSoundcard).map(Sound Card::getUSB).map(USB::getVersion)
- 21. Beyond Java 8 ❖ Functional programming: Focus on What ❖ Scala example ❖ flatten(List(List(1, 1), 2, List(3, List(5, 8)))) ❖ result: List(1, 1, 2, 3, 5, 8) ❖ Imperative programming: Focus on How ❖ Many lines needed to do the above 1-line job ❖ Functional programming is itself a great topic!