jug java7
TRANSCRIPT
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();
}
};
Questions