![Creating StreamsCreating Streams
●
Explicitly
●
From collections
●
From suppliers/generators
Stream.of(new int[] {0, 1, 2, 3, 4, 5, 6});
List<Integer> intList = new LinkedList<>();
//Initialize int list
...
intList.stream();
final Random rand = new Random();
Stream.of(()-> rand.nextInt());
IntStream.generate(() → rand.nextInt())...
LongStream.range(0, 1000L)...](https://image.slidesharecdn.com/javase8nus-140321204441-phpapp01/85/NUS-Hackers-Club-Mar-21-Whats-New-in-JavaSE-8-28-320.jpg)
;
How do you generate the byte code for the call?](https://image.slidesharecdn.com/javase8nus-140321204441-phpapp01/85/NUS-Hackers-Club-Mar-21-Whats-New-in-JavaSE-8-36-320.jpg)
invokedynamic
[#bootstrapMethod]
.this_method_name
class LangaugeRuntime {
bootstrapMethod(info) {
...
return new CallSite();
}
class AClass {
aMethod(x, y) {
...
}
CallSite
Method
Handle
1. Invoke bootstrap
2. Produces
CallSite
3.Complete linkage
4. Invokes method
implementation](https://image.slidesharecdn.com/javase8nus-140321204441-phpapp01/85/NUS-Hackers-Club-Mar-21-Whats-New-in-JavaSE-8-37-320.jpg)
NUS Hackers Club Mar 21 - Whats New in JavaSE 8?
- 1. Lee Chuk MunnLee Chuk Munn [email protected]@nus.edu.sg What's New inWhat's New in JavaSE 8?JavaSE 8?
- 2. JavaSE TimelineJavaSE Timeline JDK 1.0 Jan 1996 JDK 1.1 Feb 1997 JDK 1.2 Dec 1998 JDK 1.3 May 2000 JDK 1.4 Dec 2002 JDK 5 Sept 2004 JDK 6 Dec 2006 JDK 7 July 2011 JDK 8 Mar 2014 5 years!
- 3. What Happened?What Happened? ● Very ambitious – Modularity ● Refactor the JDK ● Native packaging – Lambda ● Language and libraries ● Lots of competing design – New bytecode to support dynamic languages – Lots of other proposed features ● Too many moving parts
- 4. Java SE 7/SE 8Java SE 7/SE 8 ● Oracle acquired Sun in 2010 ● JavaSE 7 gestation period was too long – Developers are loosing interest ● Parts of the JDK was done, some was not – Eg invokedynamic was quite solid, closures were not ● Took a poll – Deliver it in 2 parts and what is completed sooner – Or wait for everything to complete – longer
- 5. JavaSE 7JavaSE 7 ● Released on July 28 2011 ● Features – Project Coin – small change ● Integer literals, Strings in switch, type inferencing <> ● Multi-catch/precise rethrow ● Try-with-resources – NIO2 ● Paths, filesystem support, file attributes and permissions ● Async I/O, file system walker, filesystem watcher – Fork/join framework – invokedynamic
- 6. Modernizing the Java PlatformModernizing the Java Platform ● Biggest change on the Java platform since JavaSE 5 – Change the way we write Java applications ● Language – Lambda expressions – Interface evolution ● Libraries – Bulk data operations on Collections ● Platform – Profiles
- 7. LambdaLambda
- 8. Computing TodayComputing Today ● Multicore is now the default ● Need to make writing parallel code easier ● Need to make libraries smarter – Utilize the cores
- 9. Concurrency in JavaConcurrency in Java ● JDK 1.x – java.lang.Thread ● JDK 1.5 – java.util.concurrent – Locks, semaphores, Atomics – Callables – Synchronization data structures – cyclic barrier, count down latches, etc ● JDK 1.7 – Fork/join framework
- 10. What's the IssueWhat's the Issue ● Preference for doing things in libraries vs doing things in the language ● Decent job of providing easy to use parallel libraries ● Need to reduce conceptual and syntactic gap between serial and parallel – Serial and parallel code for a given task looks very different ● Need language changes to better support the libaries
- 11. Student with the Highest ScoreStudent with the Highest Score Collection<Student> students = … double highestScore = 0.0; for (Student s : students) if ((s.gradYear == 2013) && (s.score > highestScore)) highestScore = s.score;
- 12. Student with the Highest ScoreStudent with the Highest Score Collection<Student> students = ... double highestScore = 0.0; for (Student s : students) { if ((s.gradYear == 2013) && (s.score > highestScore)) highestScore = s.score; } ● Code is inherently serial – Iterate through students serially – Stateful – use of highestScore ● Client determines how to iterate the collection – Not the collection
- 13. Using Functional Language StyleUsing Functional Language Style HypotheticalCollection student = … double highestScore = student .filter(new Predicate<Student>() { public boolean op(Student s) { return (s.getGraduateYear() == 2013); } }) .map(new Mapper<Student, Double>() { public double extract(Student s) { return (s.getScore()); } }) .max(); Stateless functions and immutable data But syntactically ugly !!!
- 14. What is Closure?What is Closure? function adder(x) { return (function(y) { return (x + y); }); } var addTo3 = adder(3); Var addTo7 = adder(7); console.log(addTo3(5) + addTo7(5)); → 21 A function together with a referencing environment for the non local (free variable) variables of the function. Once defined, the free variables are bound to the function, or “closes over” it.
- 15. Lambda Expressions in JavaLambda Expressions in Java ● Lambda expressions are anonymous functions – Like a method, has a typed argument list, a return type, a set of thrown exceptions, a body – Body can be an expression or a block double highestScore = students .filter((Student s) -> s.getGradYear() == 2013) .map((Student s) -> s.getScore()) .max();
- 16. Lambda TypesLambda Types ● SAM – Single Abstract Method – Annotated with @FunctionalInterface ● Not necessary, like @Override – Ensures that the functional interface contract is honoured .map((Student s) -> s.getScore()) What is this type?
- 17. ExampleExample File srcDir = new File(“/home/cmlee/src”); for (File f: srcDir.listFiles( (File sf) -> sf.getName().endsWith(“.java”)) //Do something with f FileFilter.accept(File f) returns boolen
- 18. Target TypingTarget Typing File srcDir = new File(“/home/cmlee/src”); for (File f: srcDir.listFiles( (File sf) -> sf.getName().endsWith(“.java”)) //Do something with f FileFilter.accept(File f) returns boolen File srcDir = new File(“/home/cmlee/src”); for (File f: srcDir.listFiles( sf -> sf.getName().endsWith(“.java”)) //Do something with f Simplified to Target typing – inferring the Lambda expression type
- 19. Target TypingTarget Typing ● Same lambda expression can be assigned to different SAM FileFilter fileFilter = f -> f.getName().endsWith(“.java”); DirectoryStream.Filter<File> directoryFilter = f -> f.getName().endsWith(“.java”); Lambda literal
- 20. Method ReferenceMethod Reference ● Reuse a method as a Lambda expression – Does not have to be static – Use :: to reference it File srcDir = new File(“/home/cmlee/src”); for (File f: srcDir.listFiles(File::canRead) { //Do something with f
- 22. InterfacesInterfaces ● Methods in interfaces are cast in stone – If you do, you break backward compatibility – Classes need to be recompiled ● If you cannot change an interface you cannot refactor ● Issue with evolving libraries that are based on interfaces – Eg java.util.List, java.util.ListEx, java.util.ListEx2
- 23. Default MethodsDefault Methods ● New methods with default implementation to existing interfaces – Without recompiling the implementation class ● New implementation can decide if they want to reimplement the default methods – “Mirandarizing” the implementation package java.util; public interface List<T> { //Existing methods... ... default public void sort(Comparator<? super T> cmp) { //Sort the list ... } }
- 24. Benefits of Default MethodsBenefits of Default Methods ● Retrofitting existing API with newer capabilities – Enumeration have been superseded by Iterator interface Enumeration<E> extends Iterator<E> { //Existing Enumeration methods boolean hasMoreElements(); E nextElement(); //Methods from Iterator default boolean hasNext() { return (hasMoreElements()); } default E next() { return (nextElement()); } default void remove() { throw new UnsupportedOperationException(); } }
- 25. StreamsStreams
- 26. CollectionsCollections ● Collections are data structure – List, Set, Queue, Stack – Size of data is fixed at the point of using it ● Operations on collections can potentially mutate the state of the collection – Not thread friendly – Eg. remove() ● Values cannot be lazily generated – How do you represent and random set of positive numbers?
- 27. What are Streams?What are Streams? ● Conduit for data flow ● As the data are flowing, perform operation on them ● Streams are composable – Combine one stream with anohter ● Does not modify the source
- 28. Creating StreamsCreating Streams ● Explicitly ● From collections ● From suppliers/generators Stream.of(new int[] {0, 1, 2, 3, 4, 5, 6}); List<Integer> intList = new LinkedList<>(); //Initialize int list ... intList.stream(); final Random rand = new Random(); Stream.of(()-> rand.nextInt()); IntStream.generate(() → rand.nextInt())... LongStream.range(0, 1000L)...
- 29. Streams ExampleStreams Example Set<Student> students = … for (Student s: students) System.out.println(“Name: %s, Email: %s” , s.getName(), s.getEmail()); students.stream().forEach(s -> { System.out.println(“Name: %s, Email: %s” , s.getName(), s.getEmail()); }); Refactor to
- 30. Streams ExampleStreams Example Set<Student> students = … students.stream() .filter(s -> (2013 == s.getGradYear()) && (s.getScore() > 90)) .findAny() //Returns Optional .ifPresent(s -> { System.out.println(s); }) Print out the names of all honor students for 2013 LINQ like DSL
- 31. JavaScriptJavaScript (and dynamic language support)(and dynamic language support)
- 32. Dynamic Language SupportDynamic Language Support ● http://www.is- research.de/info/vmlanguages/category/jvm-language/ – Some are academic, experimentation – You can find a Java implementation form MOST dynamic/scripting languages – prefix with j ● JavaScript, Lua, Python, Haskell, Scheme,... – Some are JVM specific ● Scala, Groovy, Clojure – Some in serious use ● Scala, JRuby, Groovy, Clojure
- 33. Java Virtual MachineJava Virtual Machine ● Reasons for targeting the JVM – Java language != Java Virtual Machine – Mature, performant, scalable, introspection, ubiquitous ● Dynamic language support began in JDK 6 ● Integration with Java ecosystem – Large set of libraries ● Use cases – Java calling into script – adding scripting capabilities to Java application – Script calling into Java – prototyping
- 34. DemoDemo
- 35. Scripting ExampleScripting Example config.js ScriptEngine jsEngine = mgr.getEngineByName(“JavaScript”); //Application configuration bean MyAppConfig appConfig = new MyAppConfig(); //Bind appConfig to config jsEngine.put(“config”, appConfig); jsEngine.eval(new FileReader(“confing.js”)); config.server = “myserver” config.port = 12345 //Dynamically determine timeout config.timeout = calculateTimeout()
- 36. JavaScriptJavaScript this[method_name](x, y); How do you generate the byte code for the call?
- 37. invokedynamicinvokedynamic this[method_name](x, y) invokedynamic [#bootstrapMethod] .this_method_name class LangaugeRuntime { bootstrapMethod(info) { ... return new CallSite(); } class AClass { aMethod(x, y) { ... } CallSite Method Handle 1. Invoke bootstrap 2. Produces CallSite 3.Complete linkage 4. Invokes method implementation
- 38. NashornNashorn ● A new Javascript engine based on invokedynamic – To supercede Rhino in JavaSE 8 ● Why? – Node.js on Java? - https://avatar-js.java.net – Javascript container ala PhoneGap/Cordova, Adobe AIR ● Side note: javafx.scene.web.WebView – Wrapper for WebKit – Now you can display HTML pages (with JavaScript) correctly in Java
- 39. ProfilesProfiles
- 40. The Java RuntimeThe Java Runtime ● The JDK is big and monolithic – Lots of improvement over the years: warm start, memory images ● Slow startup time, memory footprint – Why should the VM load javax.swing.Jframe when you are just using classes from java.lang package? ● Single codebase – simplify engineering, better code quality – From small to big – Not the case: CLDC, CDC, JavaSE ● Versioning?
- 41. Compact ProfilesCompact Profiles ● A step toward full modularization – Coming in JavaSE 9 (I hope) ● Enable applications that use only a subset of the JavaSE platform on resource constrained devices – Eg. CLDC, CDC ● Profiles – The entire JVM and the JLS spec – Define a subset of the API – Larger profiles must be superset of smaller ones – The contents of the API packages must be the same as the full SE platform
- 42. Compact ProfilesCompact Profiles ● compact1 – 14MB – Smallest set of API packages – 14MB – java.lang, java.nio, java.util, java.net, java.security ● compact2 – 18MB – compact1 + XML + RMI + JDBC ● compact3 – 21MB – compact2 + everything except Desktop, JAX-WS/JAXB, CORBA ● Full SE – 45MB ● See https://blogs.oracle.com/jtc/entry/a_first_look_at_compact
- 43. Good Use Cases?Good Use Cases? Linux X86 Linux ARM soft float Linux ARM VFP soft float Linux ARM VFP hard float Linux PowerPC Linux PowerPC e500v2
- 44. Compact Profile ToolsCompact Profile Tools ● Restricting compiles to a profile ● Analyzing compact dependency $ jdeps -P Hello.class Hello.class -> /opt/java/jdk1.8.0/jre/lib/rt.jar (compact1) <unnamed> (Hello.class) -> java.io compact1 -> java.lang compact1 $ javac -profile compact1 Hello.class
- 45. Use The Docs Luke...Use The Docs Luke...
- 46. Embedded JavaEmbedded Java ● Can be downloaded from Oracle website ● Commercial product Prebuild profiles ejdk1.8.0 ejdk1.8.0/{architecture} ejdk1.8.0/{architecture}/compact1 ejdk1.8.0/{architecture}/compact2 ejdk1.8.0/{architecture}/compact3 ejdk1.8.0/{architecture}/jre ejdk1.8.0/{architecture}/extensions Custom profiles ejdk1.8.0/bin/jrecreate.sh
- 48. Parameter NamesParameter Names ● Reflection now returns parameter names ● Good news for all tools and framework developers ● Hypothetical example from JAX-RS @GET @Path(“{custId}”) public void get(@PathParam(“custId”) int custId) { ... @GET @Path(“{custId}”) public void get(@PathParam int custId) { ...
- 49. AnnotationAnnotation ● Annotations are pieces of information embedded in the class files – Typically used by tools to generate code, enforce certain programming practices, etc ● Processed during – Compile time – At runtime ● You can annotate – Package, class, member, constructor, method, parameters, local variable, annotation
- 50. Type AnnotationType Annotation ● Annotations can currently be used on type declarations – Package, class, member, constructor, method, parameters, local variable, annotation ● Annotations can now be used on where types are used – Permits error detection by pluggable type checkers – See http://types.cs.washington.edu/checker-framework List<@Email String> emails = new @ReadOnly LinkedList<String>(aCollection); if ((@NonNull)obj) instanceof String)
- 51. Date TimeDate Time LocalDate yesterday = LocalDate.now().minusDays(1); ZoneId.getAvailableZoneIds().stream() .forEach(tz -> { System.out.println(tz); });