Lambda functions in java 8

Lambda functions in java 8

• 1.
  …in Java 8
• 2.
  ...coming 2013
• 3.
  What’s a lambdafunction?  A.K.A.:  Anonymous function  Anonymous method  Function literal  Function constant  Closure  Wikipedia: “a function (or a subroutine) defined, and possibly called, without being bound to an identifier”  Typically can’t be recursive directly  Simple example: (int x, int y) -> x + y  Supported in a bunch of languages…
• 4.
  Already supported in…  ActionScript, C#, C++, Clojure, Curl, D, Dart, Delphi, Dylan, Erlang, F#, Frink, Go, Groovy, Haskell, JavaScript, Lisp, Logtalk, Lua, Mathematica, Maple, Matlab, Maxima, Ocaml, Octave, Objective-C, Perl, PHP, Python, R, Racket, Ruby, Scala, Scheme, Smalltalk, Vala, Visual Basic, Visual Prolog…
• 5.
  More Examples  x-> x + 1  (x) -> x + 1  (int x) -> x + 1  (int x, int y) -> x + y  (x, y) -> x + y  (x, y) -> { System.out.printf("%d + %d = %d%n", x, y, x+y); }  () -> { System.out.println("I am a Runnable"); }
• 6.
  Meanwhile, in Java7…  Functional Interfaces  SAM – “Single Abstract Method”  Interfaces that have just 1 method  java.lang.Runnable  java.util.concurrent.Callable  java.security.PrivilegedAction  java.util.Comparator  java.io.FileFilter  java.nio.file.PathMatcher  java.lang.reflect.InvocationHandler  java.beans.PropertyChangeListener  java.awt.event.ActionListener  javax.swing.event.ChangeListener
• 7.
  Meanwhile, in Java7…  Typically: button.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { panel.doStuff(e.getModifiers()); } });  Five lines to do one statement  This would become: button.addActionListener(e -> { panel.doStuff(e.getModifiers()); });
• 8.
  More Anonymous ClassIssues(?)  Lexical scoping  What does this mean? final Runnable r = () -> { // This reference to 'r' is legal: if (!allDone) { workQueue.add(r); } else { displayResults(); } };  Accessing non-final variables  Lambdas: same variable access as you’d have just outside the expression
• 9.
  java.util.functions  Predicate List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Dave"); List<String> filteredNames = names .filter(e -> e.length() >= 4) .into(new ArrayList<String>());  filter: only retain elements where the predicate holds true  into: fills up an ArrayList with the filtered elements, then gets set as filteredNames
• 10.
  java.util.functions  Block  No more for loops…? List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Dave"); names .filter(e -> e.length() >= 4) .forEach(e -> { System.out.println(e); });  forEach: Can only see one element at a time  Lazy element computation
• 11.
  java.util.functions  Method chaining List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "Dave"); names .mapped(e -> { return e.length(); }) .asIterable() // returns an Iterable of BiValue // elements; an element's key is the // person's name, its value is the // string length .filter(e -> e.getValue() >= 4) .sorted((a, b) -> a.getValue() - b.getValue()) .forEach(e -> { System.out.println(e.getKey() + 't' + e.getValue()); });  Is method chaining good…?
• 12.
  Method References  Canpass around references to methods like you can with anonymous functions by using ::  Static and instance methods Arrays.asList("Alice", "Bob", "Charlie", "Dave").forEach(System.out::println);  Make factories easily: Factory<Biscuit> biscuitFactory = Biscuit::new; Biscuit biscuit = biscuitFactory.make();
• 13.
  Default Methods  Currently, interfaces are basically “set in stone”  Altering an interface will break existing implementations  Blurred line between abstract/concrete methods…? interface Foo { void bar() default { System.out.println(“baz”); } } interface AnotherFoo extends Foo { void bar() default { System.out.println(“not baz”); } } interface YetAnotherFoo extends Foo { void bar(); }
• 14.
  More Java 8Stuff…  http://openjdk.java.net/projects/jigsaw/  Sources:  http://java.dzone.com/news/java-8-lambda- syntax-closures  http://datumedge.blogspot.ca/2012/06/java- 8-lambdas.html  http://cr.openjdk.java.net/~briangoetz/lambd a/lambda-state-4.html