Lambda Expressions in Java 8
- 1. Lambda Expressions in Java 8 Presented by: Isaac Carter
- 2. little bit about me.. Worked for the gov side of life for 4 years with ManTech and SAIC Did it all Prior to that I was in the Marines got to do a bit of traveling Now I work here at 5AM Solutions Full stack dev Interests as of late… Docker Linux Mint Cloud-computing concepts
- 3. Disclaimers I love Java, but don’t know everything about Java…especially Java 8. I’m not an expert. Feel free to ask any questions at any time. I will do my best to answer them. Any questions that I can’t answer, I promise to research and respond promptly on the MCJUG forum.
- 4. Venkat Subramaniam Basis of my talk Heard him give a talk over lambda expressions in Java 8 at NFJS conference Venkat’s amazon book list/bio
- 5. What I plan to cover… Lambda expression syntax Iterate through a list Transform a list Find elements within a list Reusing lambda expressions Code examples
- 6. Is anyone currently using Java 8?
- 7. The good parts of Java 8 Support for lambda expressions New time API Collections API has been given a major overhaul Functional interfaces Default methods Concurrency is much easier!!
- 8. …and the bad parts of Java 8 whyjavasucks.com Still no operator overloading Haven’t seen this many changes since Java 5 Lambda expressions The code is not directly readable without interpretation A developer that reads the code will need to know the code reasonably well
- 9. Java 101 It’s OO Everything is an object except primitives!! Every class creates instances of objects you can’t pass a method as an argument or return a method body for an instance Haskell and Lisp are two good examples of functional programming languages. JavaScript is consider to be one as well. (well actually both)
- 10. Java 8 can now do functional programming!!
- 11. OO v/s Functional Datafields are treated as objects manipulated through pre-defined methods Terms such as.. Inheritance Polymorphism Encapsulation Computation as the evaluation of functions
- 12. But that’s really not the best way to think about Java 8 and lambdas…
- 13. Imperative v/s Declarative Telling the machine “HOW” to do something Result = what you wanted to happen will happen Telling the machine “WHAT” you would like to happen Result = let the computer figure it out
- 14. But Isaac we love imperative programming! We are VERY used to describing the “HOW” Love controlling everything Makes us feel good and comfortable Even makes us feel powerful Don’t like to leave things up to “magic” With the power of today’s languages and compilers, we no longer need to worry about such trivial things …and this is where lambda expressions come into play…
- 15. Some quick syntax before we look at code…
- 16. Syntax of a lambda expression Basic syntax (parameters) --> (expression) (parameters) --> {statements;} Examples… () --> 5 takes no value and returns 5 x --> 2 * x takes a number and returns the result of doubling it (int x, int y) --> x + y takes two integers and returns their sum (String s) --> System.out.print(s) takes a string and prints it to the console without returning anything
- 17. Let’s look at some code examples ** only look at examples using strings **
- 18. .forEach()
- 19. Where did .forEach() come from? As of Java 8, the Iterable interface now contains the .forEach() Performs the given action for each element of the Iterable until all elements have been processed Accepts a Consumer type parameter Is a Higher Order function
- 20. Consumer
- 21. What is a Consumer??? Represents an operation that accepts only one argument and returns void ..is a functional interface …and due to this, it can be used as the assignment target for a lambda expression or method reference Example… Consumer<String> consumer = (String string) --> (System.out.println(string));
- 23. Functional interface?? Java already contains the concept of SAM interfaces Single Abstract Method interfaces Most likely have used them by creating an anonymous inner class Examples of use are...Runnable, ActionListener, and Comparator So a Functional Interface is the same as a SAM interface Java 8 is saying that they can now be represented using lambda expressions. Not going to get into the how’s and why’s of Functional Interfaces Such as.. Not required to use the @FunctionalInterface Helps the compiler Be kind to your follower developers and use the annotation
- 25. What is a Higher Order function? Means that it is possible to PASS to a method both values and functions and in the same way the method itself can return either a value or or a function Examples… public void doSomething(String name, Function some Function) {…..} public Function createAnAction(Integer someInteger) {….do some logic and return back a function..}
- 26. .stream()
- 27. What is .stream() ?? Not to be confused with InputStream or OutputStream In functional programming terms, it’s a “monad” Represents a sequence of elements and provides different kinds of operations to perform computations upon those elements Stream operations are either intermediate or terminal
- 28. Predicate
- 29. What is a Predicate ? A statement that may be true or false depending on the values of its variables Functional interface Where would you use a Predicate? Anywhere where you need to evaluate a condition on a group/collection that results in a boolean
- 30. So in summary… Learn to use lambda expressions Let Java do all the work Program more declaratively Don’t try to customize everything Unique time for programming Java is no longer just OO
- 31. Sources Lambda Expressions for Dummies Functional Programming in Java: Harnessing the power of Java 8 Lambda Expresssions Java 8 API docs Imperative v/s Declarative programming Programming Paradigms Wiki Start using Java Lambda Expressions Java Method Reference
- 32. …more sources Oracle documentation over lambdas Java 8 and Predicates