Java 7 LavaJUG

Java 7 — Julien Ponge @jponge Lava JUG

Fork / Join Project Coin NIO.2 invokedynamic (...)

Fork / Join

java.lang.Thread java.lang.Runnable wait()<5 notify() synchronized

Thread thread = new Thread() { public void run() { System.out.println(">>> Hello!"); }};thread.start();thread.join();

java.util.concurrent executors concurrent queues concurrent collections atomic variables5, 6 synchronization patterns rich locks

class Sum implements Callable<Long> { private final long from; private final long to; Sum(long from, long to) { this.from = from; this.to = to; } public Long call() { long acc = 0; for (long i = from; i <= to; i++) { acc = acc + i; } return acc; }}

ExecutorService executor = Executors.newFixedThreadPool(2);List<Future<Long>> results = executor.invokeAll(asList( new Sum(0, 10), new Sum(100, 1000), new Sum(10000, 1000000)));for (Future<Long> result : results) { System.out.println(result.get());}

1.0 Threads made easy1.11.21.31.4 5 Concurrency made easier 6 7 Parallelism made easier

Sum of an arrayn1 n2 n3 n4 n5 n6 n7 n8 n9 ... ... ... ... sum1 sum2 sum3 sum1 + sum2 sum3 + (...) total sum

How many occurrences of“java.util.List” in this ﬁlesystem tree?

Load into RAM (1 thread) Folder Document subfolders: List<Folder> lines: List<String> documents: List<Document> Divide & conquer (#cores threads)

16 Folder word counting task 10 5 1Document word Document word Folder word counting task counting task counting task 3 2 fork() Document word Document word n join() counting task counting task

ForkJoinPool Your workThread management SplitMaximize parallelism Fork subtasks Work stealing Join subtasks Compose results

ForkJoinTask join() join() RecursiveAction fork() fork() vs RecursiveTaskChild ForkJoinTask Child ForkJoinTask

(Some F/J Code)

Speedup&7"6"5"4"3"2"1" 2" 4" 6" 8" 10" 12" #cores

No I/ONo synchronization / locksDecompose in simple recursive tasksDo not decompose below a thresholdTake advantage of multicores with no painYou have more F/J candidate algorithms thanyou think!

try-with-resources

private void writeSomeData() throws IOException { DataOutputStream out = new DataOutputStream(new FileOutputStream("data")); out.writeInt(666); out.writeUTF("Hello"); out.close();}

private void writeSomeData() throws IOException { DataOutputStream out = new DataOutputStream(new FileOutputStream("data")); out.writeInt(666); out.writeUTF("Hello"); out.close();} what if...

private void writeSomeData() throws IOException { DataOutputStream out = null; try { out = new DataOutputStream(new FileOutputStream("data")); out.writeInt(666); out.writeUTF("Hello"); } finally { if (out != null) { out.close(); } }}

private void writeSomeData() throws IOException { DataOutputStream out = null; try { out = new DataOutputStream(new FileOutputStream("data")); out.writeInt(666); out.writeUTF("Hello"); } finally { if (out != null) { out.close(); } }} ...this is still far from correct!

try ( FileOutputStream out = new FileOutputStream("output"); FileInputStream in1 = new FileInputStream(“input1”); FileInputStream in2 = new FileInputStream(“input2”)) { // Do something useful with those 3 streams! // out, in1 and in2 will be closed in any case out.write(in1.read()); out.write(in2.read());}

public class AutoClose implements AutoCloseable { @Override public void close() { System.out.println(">>> close()"); throw new RuntimeException("Exception in close()"); } public void work() throws MyException { System.out.println(">>> work()"); throw new MyException("Exception in work()"); }}

AutoClose autoClose = new AutoClose();try { autoClose.work();} finally { autoClose.close();}

AutoClose autoClose = new AutoClose();try { autoClose.work();} finally { autoClose.close();}>>> work() >>> close() java.lang.RuntimeException: Exception in close() at AutoClose.close(AutoClose.java:6) at AutoClose.runWithMasking(AutoClose.java:19) at AutoClose.main(AutoClose.java:52)

AutoClose autoClose = new AutoClose();try { autoClose.work();} finally { autoClose.close();} MyException m asked by Run>>> work() time Exception >>> close() java.lang.RuntimeException: Exception in close() at AutoClose.close(AutoClose.java:6) at AutoClose.runWithMasking(AutoClose.java:19) at AutoClose.main(AutoClose.java:52)

“Caused by” ≠ “Also happened”

AutoClose autoClose = new AutoClose();MyException myException = null;try { autoClose.work();} catch (MyException e) { myException = e; throw e;} finally { if (myException != null) { try { autoClose.close(); } catch (Throwable t) { myException.addSuppressed(t); } } else { autoClose.close(); }}

try (AutoClose autoClose = new AutoClose()) { autoClose.work();}

try (AutoClose autoClose = new AutoClose()) { autoClose.work(); }>>> work() >>> close() MyException: Exception in work() at AutoClose.work(AutoClose.java:11) at AutoClose.main(AutoClose.java:16) Suppressed: java.lang.RuntimeException: Exception in close() at AutoClose.close(AutoClose.java:6) at AutoClose.main(AutoClose.java:17)

public void compress(String input, String output) throws IOException { try( FileInputStream fin = new FileInputStream(input); FileOutputStream fout = new FileOutputStream(output); GZIPOutputStream out = new GZIPOutputStream(fout) ) { byte[] buffer = new byte[4096]; int nread = 0; while ((nread = fin.read(buffer)) != -1) { out.write(buffer, 0, nread); } }}

public void compress(String input, String output) throws IOException { public void compress(String paramString1, String paramString2) try( throws IOException { FileInputStream fin = new FileInputStream(input); FileInputStream localFileInputStream = new FileInputStream(paramString1); FileOutputStream fout = new FileOutputStream(output); Object localObject1 = null; GZIPOutputStream out = new GZIPOutputStream(fout) try { ) { FileOutputStream localFileOutputStream = new FileOutputStream(paramString2); byte[] buffer = new byte[4096]; Object localObject2 = null; int nread = 0; try { while ((nread = fin.read(buffer)) != -1) { GZIPOutputStream localGZIPOutputStream = new GZIPOutputStream(localFileOutputStream); out.write(buffer, 0, nread); Object localObject3 = null; } try { } byte[] arrayOfByte = new byte[4096];} int i = 0; while ((i = localFileInputStream.read(arrayOfByte)) != -1) { localGZIPOutputStream.write(arrayOfByte, 0, i); } } catch (Throwable localThrowable6) { localObject3 = localThrowable6; throw localThrowable6; } finally { if (localGZIPOutputStream != null) { if (localObject3 != null) { try { localGZIPOutputStream.close(); } catch (Throwable localThrowable7) { localObject3.addSuppressed(localThrowable7); } } else { localGZIPOutputStream.close(); } } } } catch (Throwable localThrowable4) { localObject2 = localThrowable4; throw localThrowable4; } finally { if (localFileOutputStream != null) { if (localObject2 != null) { try { localFileOutputStream.close(); } catch (Throwable localThrowable8) { localObject2.addSuppressed(localThrowable8); } } else { localFileOutputStream.close(); } } } } catch (Throwable localThrowable2) { localObject1 = localThrowable2; throw localThrowable2; } finally { if (localFileInputStream != null) { if (localObject1 != null) { try { localFileInputStream.close(); } catch (Throwable localThrowable9) { localObject1.addSuppressed(localThrowable9); } } else { localFileInputStream.close(); } } } }

Not just syntactic sugarClutter-free, correct codeclose(): - be more speciﬁc than java.lang.Exception - no exception if it can’t fail - no exception that shall not be suppressed (e.g., java.lang.InterruptedException)

Diamond <>

List<String> strings = new LinkedList<Integer>();Map<String, List<String>> contacts = new HashMap<Integer, String>();

List<String> strings = new LinkedList<String>();strings.add("hello");strings.add("world");Map<String, List<String>> contacts = new HashMap<String, List<String>>();contacts.put("Julien", new LinkedList<String>());contacts.get("Julien").addAll(asList("Foo", "Bar", "Baz"));

List<String> strings = new LinkedList<>();strings.add("hello");strings.add("world");Map<String, List<String>> contacts = new HashMap<>();contacts.put("Julien", new LinkedList<String>());contacts.get("Julien").addAll(asList("Foo", "Bar", "Baz"));

Map<String, String> map = new HashMap<String, String>() { { put("foo", "bar"); put("bar", "baz"); }};

Map<String, String> map = new HashMap<>() { { put("foo", "bar"); put("bar", "baz"); }};

Map<String, String> map = new HashMap<>() { { put("foo", "bar"); put("bar", "baz"); }};Diamond.java:43: error: cannot infer type arguments for HashMap; Map<String, String> map = new HashMap<>() { ^ reason: cannot use <> with anonymous inner classes1 error

class SomeClass<T extends Serializable & CharSequence> { } Non-denotable type

class SomeClass<T extends Serializable & CharSequence> { } Non-denotable typeSomeClass<?> foo = new SomeClass<String>();SomeClass<?> fooInner = new SomeClass<String>() { };SomeClass<?> bar = new SomeClass<>();SomeClass<?> bar = new SomeClass<>() { };

class SomeClass<T extends Serializable & CharSequence> { } Non-denotable typeSomeClass<?> foo = new SomeClass<String>();SomeClass<?> fooInner = new SomeClass<String>() { };SomeClass<?> bar = new SomeClass<>();SomeClass<?> bar = new SomeClass<>() { }; No denotable type to generate a class

Less ceremony when using genericsNo diamond with inner classes

Simpliﬁed varargs

private static <T> void doSomethingBad(List<T> list, T... values) { values[0] = list.get(0);}public static void main(String[] args) { List list = Arrays.asList("foo", "bar", "baz"); doSomethingBad(list, 1, 2, 3);}

This yields warnings + crash:private static <T> void doSomethingBad(List<T> list, T... values) { values[0] = list.get(0);}public static void main(String[] args) { List list = Arrays.asList("foo", "bar", "baz"); doSomethingBad(list, 1, 2, 3);} Heap Pollution: List = List<String>

private static <T> void doSomethingGood(List<T> list, T... values) { for (T value : values) { list.add(value); }}

private static <T> void doSomethingGood(List<T> list, T... values) { for (T value : values) { list.add(value); }}$ javac Good.javaNote: Good.java uses unchecked or unsafe operations.Note: Recompile with -Xlint:unchecked for details.

@SuppressWarnings({“unchecked”,“varargs”})public static void main(String[] args) { List<String> list = new LinkedList<>(); doSomethingGood(list, "hi", "there", "!");}$ javac Good.java$

static, ﬁnal methods, constructors@SafeVarargsprivate static <T> void doSomethingGood(List<T> list, T... values) { for (T value : values) { list.add(value); }}

Mark your code as safe for varargsYou can’t cheat with @SafeVaragsRemove @SuppressWarnings in client codeand pay attention to real warnings

Multi-catch & more precise rethrow

Class<?> stringClass = Class.forName("java.lang.String");Object instance = stringClass.newInstance();Method toStringMethod = stringClass.getMethod("toString");System.out.println(toStringMethod.invoke(instance));

try { Class<?> stringClass = Class.forName("java.lang.String"); Object instance = stringClass.newInstance(); Method toStringMethod = stringClass.getMethod("toString"); System.out.println(toStringMethod.invoke(instance));} catch (ClassNotFoundException e) { e.printStackTrace();} catch (InstantiationException e) { e.printStackTrace();} catch (IllegalAccessException e) { e.printStackTrace();} catch (NoSuchMethodException e) { e.printStackTrace();} catch (InvocationTargetException e) { e.printStackTrace();}

try { Class<?> stringClass = Class.forName("java.lang.String"); Object instance = stringClass.newInstance(); Method toStringMethod = stringClass.getMethod("toString"); System.out.println(toStringMethod.invoke(instance));} catch (Throwable t) { t.printStackTrace();}

try { Class<?> stringClass = Class.forName("java.lang.String"); Object instance = stringClass.newInstance(); Method toStringMethod = stringClass.getMethod("toString"); System.out.println(toStringMethod.invoke(instance));} catch (Throwable t) { t.printStackTrace();} How about SecurityException?

try { Class<?> stringClass = Class.forName("java.lang.String"); Object instance = stringClass.newInstance(); Method toStringMethod = stringClass.getMethod("toString"); System.out.println(toStringMethod.invoke(instance));} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) { e.printStackTrace();} Union of alternatives

catch (SomeException e)Now implicitly ﬁnal unless assigned...

static class SomeRootException extends Exception { }static class SomeChildException extends SomeRootException { }static class SomeOtherChildException extends SomeRootException { }public static void main(String... args) throws Throwable {try { throw new SomeChildException();} catch (SomeRootException firstException) { try { throw firstException; } catch (SomeOtherChildException secondException) { System.out.println("I got you!"); }}

static class SomeRootException extends Exception { }static class SomeChildException extends SomeRootException { }static class SomeOtherChildException extends SomeRootException { }public static void main(String... args) throws Throwable {try { throw new SomeChildException();} catch (SomeRootException firstException) { try { throw firstException; } catch (SomeOtherChildException secondException) { System.out.println("I got you!"); }}$ javac Imprecise.javaImprecise.java:13: error: exception SomeOtherChildException is never thrown in body ofcorresponding try statement } catch (SomeOtherChildException secondException) { ^1 error

Less clutterBe preciseDo not capture unintended exceptionsBetter exception ﬂow analysis

Minor additions

// 123 in decimal, octal, hexadecimal and binarybyte decimal = 123;byte octal = 0_173;byte hexadecimal = 0x7b;byte binary = 0b0111_1011;// Other valuesdouble doubleValue = 1.111_222_444F;long longValue = 1_234_567_898L;long longHexa = 0x1234_3b3b_0123_cdefL;

public static boolean isTrue(String str) { switch(str.trim().toUpperCase()) { case "OK": case "YES": case "TRUE": return true; case "KO": case "NO": case "FALSE": return false; default: throw new IllegalArgumentException("Not a valid true/false string."); }}

public static boolean isTrue(String s) { String str = s.trim().toUpperCase(); int jump = -1; switch(str.hashCode()) { case 2404: if (str.equals("KO")) { jump = 3; Bucket } break;(...) switch(jump) {(...) case 3: case 4: case 5: return false; default: Real code throw new IllegalArgumentException( "Not a valid true/false string."); }}

Oracle Technology Network (more soon...) Fork and Join: Java Can Excel at Painless Parallel Programming Too! http://goo.gl/tostz Better Resource Management with Java SE 7: Beyond Syntactic Sugar http://goo.gl/7ybgr

Julien Ponge @jponge http://gplus.to/jpongehttp://julien.ponge.info/julien.ponge@insa-lyon.fr

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Java 7 LavaJUG

by julien.ponge on Oct 14, 2011

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