jug java7

Java 7 new features

Java User Group Latviawww.jug.lv

Java 7Project began in August 2006JDK7 is done via Open JDK effortMajor release – JVM, language and library changesCurrent status – milestone M10, build b115, planned release Mid 2011

Initially planned featuresClosures – Project LambdaSmall language changes – Project CoinModularity for Java platform – Project JigsawSupport for dynamically-typed languagesCore and IO library extensionsSwing and UI related changesSupport for updated standards - Unicode, localization, security, cryptography, XML and JDBC

Two release plansPlan A

All features, release in Mid 2012Plan B

JDK 7 minus Lambda, Jigsaw and part of Coin, release in Mid 2011JDK 8, release in late 2012

Plan B selectedPlan A

All features, release in Mid 2012Plan B

JDK 7 minus Lambda, Jigsaw and part of Coin, release in Mid 2011JDK 8, release in late 2012

Approved feature listJSR 292: Support for Dynamically-Typed Languages (“InvokeDynamic”)Small Language Enhancements (Project Coin)Concurrency and Collections Updates (including the Fork/Join Framework)Upgrade Class-Loader ArchitectureUnicode 6.0JSR 203: More New I/O APIs (“NIO 2”)Updated cryptographyJDBC 4.1Translucent & Shaped WindowsHeavyweight/Lightweight Component MixingSwing: Nimbus Look-and-Feel, JLayer ComponentUpdate the XML Stack (JAXP, JAXB, & JAX-WS)

Language enhancements - Project Coin

Strings in switch statementGregorianCalendar c = new GregorianCalendar();

int monthNameToDays(String s, int year) {

switch (s) {

case "April": case "June":

case "September": case "November":

return 30;

case "January": case "March":

case "May": case "July":

case "August": case "December":

return 31;

case "February":

return 28 + (c.isLeapYear(year) ? 1 : 0);

default:

return -1;

}

}

Improved Type Inference for Generic Instance Creation

Map<Integer, List<String>> map =

new HashMap<Integer, List<String>>();

New “diamond” operator:

Map<Integer, List<String>> map = new HashMap<>();

List<?> l = new ArrayList<>();

Try-with-resourcesvoid copy(String src, String dest) throws IOException {

InputStream in = new FileInputStream(src);

try {

OutputStream out = new FileOutputStream(dest);

try {

byte[] buf = new byte[8 * 1024];

int n;

while ((n = in.read(buf)) >= 0)

out.write(buf, 0, n);

} finally {

out.close();

}

} finally {

in.close();

}

}

Try-with-resources

void copy(String src, String dest) throws IOException {

try (InputStream in = new FileInputStream(src);

OutputStream out = new FileOutputStream(dest)) {

byte[] buf = new byte[8192];

int n;

while ((n = in.read(buf)) >= 0)

out.write(buf, 0, n);

}

}

Try-with-resources

void copy(String src, String dest) {

try (InputStream in = new FileInputStream(src);

OutputStream out = new FileOutputStream(dest)) {

byte[] buf = new byte[8192];

int n;

while ((n = in.read(buf)) >= 0)

out.write(buf, 0, n);

} catch (IOException e) {

e.printStackTrace();

}

}

Try-with-resources

package java.lang;

public interface AutoCloseable {

void close() throws Exception;

}

package java.io;

public interface Closeable extends AutoCloseable {

void close() throws IOException;

}

Multi-catch

try {

String.class.newInstance();

} catch (final IllegalAccessException | InstantiationException e) {

e.printStackTrace();

throw e;

} catch (Exception e) {

// handle exception

}

Integer and binary literals

byte b = 0b00100101;

int phoneNumber = 123_456_7890;

long creditCardNumber = 1234_5678_9012_3456L;

int hexBytes = 0xFF_EC_DE_5E;

Simplified Varargs Method Invocation

List<String> a = new ArrayList<String>(),

b = new ArrayList<String>(),

c = new ArrayList<String>();

// Warning: [unchecked] unchecked generic array

// creation for varargs parameter of type

// List<String>[]

return Arrays.asList(a, b, c);

Language enhancements postponed until Java 8

Language enhancements in Java 8

Collection literals and indexing

List<String> cities = ["Riga", "London", "Tokio"];

Set<String> countries = { "LV", "LT", "EE" };

Map<String, Double> atomicWeights = { "H" : 1.0079,

"He" : 4.0026, "Li" : 6.941 };

String city = cities[0];

Double weight = atomicWeights["H"];

Language enhancements in Java 8

Closures

#{ int x -> x + 1 }

#{ System.out.println("Hello, World!") }

list.forEach(#{ e -> System.out.println(e) });

Arrays.sort(array, #{ a, b -> a.compareToIgnoreCase(b) });

Language enhancements in Java 8

Method references

class Person {

public static int compareByAge(Person a, Person b) { ... }

}

Person[] people = ...

Arrays.sort(people, #Person.compareByAge);

Arrays.sort(people, #Person.compareByAge(Person, Person));

Arrays.sort(people, #comparatorHolder.comparePersonByAge);

JSR 292 – Support for Dynamically-Typed languages

JSR 292 - OverviewDynamic languages on the JVMJSR 223 implemented in JDK6JVM initially designed for statically-typed language4 bytecode instructions available for method invocations

InvokestaticInvokevirtualInvokespecialInvokeinterface

new bytecode instruction "invokedynamic“ and Method Handlesjava.dyn package

JSR 292 – Method HandlesMethod handle is a lightweight pointer or reference to a methodjava.dyn.MethodHandleExample

public void testMethodHandle() throws Throwable {

MethodHandle hndl = MethodHandles.lookup().findVirtual(

PrintStream.class, "println",

MethodType.methodType(void.class, String.class));

hndl.<void>invokeGeneric(System.out, "Hello, MethodHandle!");

}

JSR 292 Invokedynamic – how it works?

JVM encounters invokedynamic instructionJVM invokes the bootstrap methodThe Bootstrap method resolves the method handleThe Bootstrap method must be previously registered in JVMFuture calls don't require the Bootstrap method invocation

JSR 292 InvokeDynamic, Java example

public void testDynamic() throws Throwable {InvokeDynamic.<void>greet("World");

}

static {Linkage.registerBootstrapMethod("bootstrap");

}

public static void greet(String str) {System.out.println("Hello, dynamic " + str);

}

private static CallSite bootstrap(Class caller, String name, MethodType type) {CallSite site = new CallSite(caller, name, MethodType.make(void.class));site.setTarget(MethodHandles.lookup().findStatic(Test.class, name, MethodType.make(void.class, String.class)));return site;

}

NIO.2

NIO.2 – Pathsjava.nio.file.Path – a replacement for java.io.File

File file = new File("index.html");

Path path = Paths.get("index.html");

Path path = new File("index.html").toPath();

All Path methods throw exceptions in case of errors

if (!file.delete()){ ... }

try { path.delete(); } catch (IOException e) {

...}

NIO.2 – FileSystemProvides interface to file systemDefault file system is local/platform file system

FileSystem local = FileSystems.getDefault();

Path p = local.getPath(“filename");

Path p2 = Paths.get(“filename”);

Jar and Zip file systems included

NIO.2 – DirectoryStream

DirectoryStream to iterate over the entriesScales to large directoriesFilter using glob, regex, or custom filter

try (DirectoryStream<Path> stream =

dir.newDirectoryStream("*.{c,h,cpp,hpp,java}")) {

for (Path entry : stream) {

...

}

}

NIO.2 - Files.walkFileTree

Walks a file tree rooted at a given starting fileInvoke FileVisitor method for each file/directory

interface FileVisitor<T> {

FileVisitResult preVisitDirectory(T dir);

FileVisitResult visitFile(T file, BasicFileAttributes attrs);

FileVisitResult visitFileFailed(T file, IOException exc);

FileVisitResult postVisitDirectory(T dir, IOException exc);

}

SimpleFileVisitor – a default implementation

NIO.2 - File change notifications

Current approach – polling the file systemWatchService – watch registered objects (Watchables) for changes

WatchService watcher = path.getFileSystem().newWatchService();

path.register(watcher, ENTRY_CREATE, ENTRY_MODIFY); for (;;) { WatchKey watchKey = watcher.take(); for (WatchEvent event : watchKey.pollEvents()) { System.out.println(event.kind() + " : “ + event.context()); } watchKey.reset();}

Fork/Join framework

Fork/Join FrameworkMulticore era approachingMoore’s Law doesn’t work since ~2003Current solution (java.util.concurrent) has its limitations

Coarse grained parallelismInefficient CPU utilization

Solution: Fork/Join framework

Fork/Join – Divide and conquer

Result solve(Problem problem) {

if (problem.size < SEQUENTIAL_THRESHOLD)

return solveSequentially(problem);

else {

Result left, right;

INVOKE-IN-PARALLEL {

left = solve(extractLeftHalf(problem));

right = solve(extractRightHalf(problem));

}

return combine(left, right);

}

}

Fork/Join - architectureForkJoinExecutor, ForkJoinTaskEach worker thread has it’s own task queue (deque) – no concurrency between treads for tasksWork stealing algorithm – threads are never idle

Fork/Join - ParallelArrayParallelArray<T>, ParallelLongArray etc.Supports filtering, mapping, searching, sorting, reducing etc.

ParallelArray exampleParallelArray<Order> orders = new ParallelArray<>(fjPool, data);

double maxAmount = orders

.withFilter(madeThisYear)

.withMapping(getAmount)

.max();

static final Ops.Predicate<Order> madeThisYear = new Ops.Predicate<>() {

public boolean op(Order o) {

return o.getYear() == thisYear;

}

};

static final Ops.ObjectToDouble<Order> getAmount = new Ops.ObjectToDouble<>() {

public double op(Order o) {

return o.getAmount();

}

};

Try it yourselfDownload JDK 7 early access https://jdk7.dev.java.net/

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