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- 1. Functional Programming with Java MehdiEinali Advanced Programming in Java 1
- 2. 2 agenda Java versions Default method Functionalinterface Double colon Functional programing Lambda expression Optional Streams
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- 4. 4 Java versions-1 Version ReleaseDate Main Features 1.0 1996 The first stable version 1.1 1997 • an extensive retooling of the AWT event model • Inner classes added to language • Reflection • I18n and Unicode Support 1.2(j2se) 1998 • Swing Framework • Collection Framework 1.3 2000 • Java performance engine Hotspot added • RMI added 1.4 2002 • Regular Expression support • Exception Handling high-level api added • Non-Blocking IO(NIO 1) added • Java Web Start
- 5. 5 Java versions-2 Version ReleaseDate Main Features 1.5(J2SE 5) 2004-2009 22 update • Generic Types • Annotation • Autoboxing • Enumorations • Varargs • Foreach 1.6(J2SE 6) 2006-2013 More than 50 updates Last one 113 • Performance improvements • Security Improvements • JDBC 4 J2SE 7 2011-now Many update Last one 101 • String in switch • NIO 2 • Diamond in generic types • Concurrency high level API
- 6. 6 Java versions-3 Version ReleaseDate Main Features Java SE 8 2014-now Last update 92 • Lambda expression or closure (Functional Programming) • JavaScript embedded emulator • Annotation on Java Type • default method in interface Java SE 9 Scheduled for March 2017 • Better support for multi-gigabyte heaps • Java module system (OSGI like built-in system) • Reactive Streams support • Better support for parallel systems Java SE 10 Scheduled for March 2018 • Object without Identity • Support 64-bit addressable arrays
- 7. 7 Default method ininterfaces
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- 10. 10 Default method In ‘thestrictest sense’, Default methods are a step backwards because they allow you to ‘pollute’ your interfaces with code they provide the most elegant way to allow backwards compatibility The implementation will be used as default if a concrete class does not provide implementation for that method.
- 11. 11 Notes on default defaultmethod can only access its arguments as interfaces do not have any state. Remember interface don’t have object state and its fields are implicitly public static final You can write static method in interface and call it from default method Both on them don’t depend on method arguments and class variables rather than object state All method declarations in an interface, including static methods, are implicitly public, so you can omit the public modifier.
- 12. 12 Notes on default Whenwe extend an interface that contains a default method, we can perform following: Not override the default method and will inherit the default method. Override the default method similar to other methods we override in subclass. Redeclare default method as abstract, which force subclass to override it
- 13. 13 Conflicts multiple interface Sinceclasses in java can implement multiple interfaces, there could be a situation where 2 or more interfaces has a default method with the same signature hence causing conflicts as java will not know what methods to use at a time.
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- 15. 15 Java programing paradigms Priorto JavaSE 8, Java supported three programming paradigms procedural programming object-oriented programming generic programming. Java SE 8 adds functional programming programming that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. Stateless functions is building block of code
- 16. 16 Why functional programing? Multicore and multi thread processor increase every day Functions can pass as building block of computations. Distributes on threads Collections is every important data structure in algorithms In memory storage paradigms are increasing Collection operations is more frequent process consuming codes
- 17. 17 collection iteration External iteration Developercode do iterations What you want to accomplish collection oriented task and how Disadvantages: Its error prone (keep all intermediate variables consistent) Duplicate logic In be optimized in library level Internal iterations Just say what you want to accomplish collection oriented task.
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- 20. 20 Functional interface An interfacethat contains exactly one abstract method (and may also contain default and static methods).also known as single abstract method (SAM) interfaces Functional interfaces are used extensively in functional programming, because they act as an object oriented model for a function. To ensure that your interface meet the requirements, you should add the optional @FunctionalInterface annotation. java.util.function package for basic functional interfaces
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- 24. 24 Double colon staticmethod Java 8 enables you to pass references of methods or constructors via the :: keyword
- 25. 25 Double colon objectmethod
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- 28. 28 Lambda expressions Functional programmingis accomplished with lambda expressions. A lambda expression represents an anonymous method—a shorthand notation for implementing a functional interface, similar to an anonymous inner class A lambda consists of a parameter list followed by the arrow token (->) and a body (parameterList) -> {statements} (int x, int y) -> {return x + y;}
- 29. 29 syntax When the bodycontains only one expression, the return keyword and curly braces may be omitted, as in: (x, y) -> x + y in this case, the expression’s value is implicitly returned When the parameter list contains only one parameter, the parentheses may be omitted, as in value -> System.out.printf("%d ", value) () -> System.out.println("Welcome to lambdas!")
- 30. 30 scoping Accessing outer scopevariables from lambda expressions is very similar to anonymous objects. You can access effectively final variables from the local outer scope as well as instance fields and static variables. effectively final means: Explicitly final Implicitly final: not explicit final keyword but acts as final variable
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- 33. 33 optional Optionals are notfunctional interfaces, instead it's a nifty utility to prevent NullPointerException. Optional is a simple container for a value which may be null or non-null. Think of a method which may return a non-null result but sometimes return nothing. Instead of returning null you return an Optional in Java 8.
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- 36. 36 streams A java.util.Stream representsa sequence of elements on which one or more operations can be performed Stream operations are either intermediate or terminal. terminal operations return a result of a certain type intermediate operations return the stream itself so you can chain multiple method calls in a row Stream operations can either be executed sequential or parallel.
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- 39. 39 Parallel stream Streams canbe either sequential or parallel. Operations on sequential streams are performed on a single thread while operations on parallel streams are performed concurrent on multiple threads.
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