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Java 7 Features and Enhancements

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Contains Java 7 main features and enhancements from developers perspective

Contains Java 7 main features and enhancements from developers perspective

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  • 1. Java 7 Features and Enhancements Gagan Agrawal
  • 2. AgendaFork and Join FrameworkNew File System API(NIO 2.0) Asynchronous I/O Custom File System ProviderDynamic Language SupportThe try-with resources StatementImproved Exception HandlingOther improvements Underscores in Numeric Literals String in switch Statement Diamond Operator
  • 3. Fork and JoinFork/Join framework is an implementation of ExecutorService interface.Helps to take advantage of multiple processors.It is designed for work that can be broken into smaller pieces recursively.The goal is to use all the available processing power to make application wicked fast.Fork/Join framework distributes tasks to worker threads in a thread pool.It uses a work-stealing algorithmWorker threads that run out of things to do can steal tasks from other threads that are still busy
  • 4. Fork and JoinSuitable for work that can be broken into smaller pieces
  • 5. Fork and JoinWorks on "divide and conquer" algorithmAlso referred to as "map and reduce" Map Phase : Splitting the data space to be processed by an algorithm into smaller, independent chunks. Reduce Phase : Collection of partial results to form the final result once a set of chunks has been processed.
  • 6. Fork and JoinBasic Use if (my portion of the work is small enough) do the work directly else split my work into two pieces invoke the two pieces and wait for the results
  • 7. Fork and Join
  • 8. Fork and JoinImportant Classes ForkJoinPool - An ExecutorService for running ForkJoinTasks. ForJoinTask - Abstract base class for tasks that run within a ForkJoinPool RecursiveAction : A recursive resultless ForkJoinTask RecursiveTask : A recursive result-bearing ForkJoinTask.
  • 9. Fork and JoinTypical Steps :Partition into subproblems - Break up main problem into several parts. Each part should be as independent as possible.Create subtasks - Construct each solution to each part as a ForkJoinTask.Fork subtasks - Feed subtasks to pool of worker threads. Base pool size on number of CPUs or other resource considerations.Join subtasks - Wait out processing of as manysubtasks (usually all) needed to compose solutionCompose solution - Compose overall solution from completed partial solutions.
  • 10. Fork and JoinSome FactsDifferent kind of tasks Computation-intensive I/O-intensive Event-intensiveMost useful with Computation-intensive tasksNormally best to have one worker thread per CPUEach new task is queued in current worker thread’s dequeue (double- ended queue)Workers run tasks from their own dequeues in stack-based LIFO (i.e., newest task first) order.If a worker is idle, it steals a task, in FIFO (oldest task first) order from another thread’s dequeue or entry queue
  • 11. Fork and JoinWork Stealing
  • 12. New file system API (NIO 2.0)New package java.nio.file to access files, file attributes and file systems.New classes to ease life of developer when working with multiple file systems. Path Paths FileSystem FileSystems Files
  • 13. New file system API (NIO 2.0) File I/O Methods Arranged from Less Complex to More Complex
  • 14. New file system API (NIO 2.0)OpenOptions Parameters WRITE – Opens the file for write access. APPEND – Appends the new data to the end of the file. This option is used with the WRITE or CREATE options. TRUNCATE_EXISTING – Truncates the file to zero bytes. This option is used with the WRITE option. CREATE_NEW – Creates a new file and throws an exception if the file already exists. CREATE – Opens the file if it exists or creates a new file if it does not. DELETE_ON_CLOSE – Deletes the file when the stream is closed. This option is useful for temporary files. SPARSE – Hints that a newly created file will be sparse. This advanced option is honored on some file systems, such as NTFS, where large files with data "gaps" can be stored in a more efficient manner where those empty gaps do not consume disk space. Example : Path path = Paths.get("file.txt") OutputStream out = Files.newOutputStream(path, CREATE, APPEND);
  • 15. New file system API (NIO 2.0)File Creation supports optional set of initial attributes. e.g. For UNIX based file system one can specify Owner Group Owner File permissions at the time file is created.
  • 16. New file system API (NIO 2.0)Reading All Bytes or Lines from a File readAllBytes(Path) readAllLines(Path, Charset) Path file = Paths.get("c:Tempxyz.txt"); byte[] fileArray = Files.readAllBytes(file);Writing All Bytes or Lines to a File write(Path, byte[], OpenOption...) write(Path, Iterable< extends CharSequence>, Charset, OpenOption...) Path file = Paths.get("c:Tempxyz.txt"); byte[] buf = ...; Files.write(file, buf);
  • 17. New file system API (NIO 2.0)Methods for Creating Regular and Temporary Files Creating Regular Files Path sourceFile = Paths.get("source.txt"); Path newFile = Paths.get("new.txt"); PosixFileAttributes attrs = Files.readAttributes(sourceFile, PosixFileAttributes.class); FileAttribute<Set<PosixFilePermission>> attr = PosixFilePermissions.asFileAttribute(attrs.permissions()); Files.createFile(newFile, attr); *************************************************************************************** Path file = Paths.get("test.txt"); Set<PosixFilePermission> perms = PosixFilePermissions.fromString("rw-------"); FileAttribute<Set<PosixFilePermission>> attr = PosixFilePermissions.asFileAttribute(perms); Files.setPosixFilePermissions(file, perms);
  • 18. New file system API (NIO 2.0)Creating Temporary FilesOne of the following methods can be used Files.createTempFile(Path dir,String prefix,String suffix,FileAttribute<?>... attrs) Allows to specify the directory in which temporary file will be created. Files.createTempFile(String prefix,String suffix,FileAttribute<?>... attrs) Creates new file in default temporary file directory. *********************************************************************************************** try { Path tempFile = Files.createTempFile(null, ".myapp"); System.out.format("The temporary file has been created: %s%n", tempFile) ; } catch (IOException x) { System.err.format("IOException: %s%n", x); } ************************************************************************************************ Result The temporary file has been created: /tmp/509668702974537184.myapp
  • 19. New file system API (NIO 2.0)Reading a File by Using Buffered Stream I/O BufferedReader reader = Files.newBufferedReader(path, charset)Writing a File by Using Buffered Stream I/O BufferedWriter writer = Files.newBufferedWriter(path, charset)Similar methods exists for InputStream and OutputStream InputStream in = Files.newInputStream(path) OutputStream os = Files.newOutputStream(path)
  • 20. New file system API (NIO 2.0)Access Control Lists(ACL) Adds entry to existing ACL to grant "joe" access
  • 21. New file system API (NIO 2.0)Managing Metadata size(Path) - Returns the size of the specified file in bytes. isDirectory(Path, LinkOption) - Returns true if the specified Path locates a file that is a directory. isRegularFile(Path, LinkOption...) - Returns true if the specified Path locates a file that is a regular file. isSymbolicLink(Path) - Returns true if the specified Path locates a file that is a symbolic link. isHidden(Path) - Returns true if the specified Path locates a file that is considered hidden by the file system. getLastModifiedTime(Path, LinkOption...) / setLastModifiedTime(Path, FileTime) - Returns or sets the specified files last modified time. getOwner(Path, LinkOption...) / setOwner(Path, UserPrincipal) - Returns or sets the owner of the file. getPosixFilePermissions(Path, LinkOption...) / setPosixFilePermissions(Path, Set<PosixFilePermission>) - Returns or sets a files POSIX file permissions. getAttribute(Path, String, LinkOption...) / setAttribute(Path, String, Object, LinkOption...) - Returns or sets the value of a file attribute.
  • 22. New file system API (NIO 2.0)File change notifications WatchService API – To receive notification events upon changes to the subject (directory or file). Create a WatchService. This service consists of a queue to hold WatchKeys Register the directory/file you wish to monitor with this WatchService While registering, specify the types of events to receive (create, modify or delete events) Start an infinite loop to listen to events When an event occurs, a WatchKey is placed into the queue Consume the WatchKey and invoke queries on it
  • 23. Asynchronous I/OAsynchronous I/O API for both sockets and files.Asynchronous channel represent a connection that supports nonblocking operations e.g connecting, reading or writing.Provides mechanisms for controlling the operations after they have been initiated. Future Style – Initiate I/O operation, returning java.util.concurrent.Future Callback Style – Specify CompletionHandler when invoking I/O operation. CompletionHandler invoked when I/O operation completes.
  • 24. Asynchronous I/OAsynchronous Channel APIs AsynchronousSocketChannel AsynchronousServerSocketChannel AsynchronousFileChannel AsynchronousDatagramChannel
  • 25. Asynchronous I/OFuture Style (Server setup)
  • 26. Asynchronous I/OFuture Style (Client setup)Reading/Writing – Client/Server
  • 27. Asynchronous I/OCallback Style Create CompletionHandler Open a file For Reading For Reading/Writing Write content to file
  • 28. Asynchronous I/OAsynchronous Channel Groups Each asynchronous channel constructed belongs to a channel group that shares a pool of Java threads. They are used for handling the completion of initiated asynchronous I/O operations. By default, channels constructed with the open() methods belong to a global channel group. That can be configured using the following system variables: java.nio.channels.DefaultThreadPoolthreadFactory - defines a java.util.concurrent.ThreadFactory to use instead of the default one java.nio.channels.DefaultThreadPool.initialSize - specifies the thread pools initial size
  • 29. Asynchronous I/OThree utility methods in java.nio.channels.AsynchronousChannelGroup provide a way to create new channel groups: withCachedThreadPool() withFixedThreadPool() withThreadPool()
  • 30. Custom File System ProviderThe NIO 2.0 API provides the ability to develop a custom file system provider.A file system is essentially a container with organized, homogenous elements referred to as file system objectsA file system provides access to file system objects.A file system object can be a File store File Directory
  • 31. Custom File System ProviderA file store is a volume or partition in which files are storedFor e.g in Windows, C: and D: are file storesOn the Solaris operating system, / (root) and mounted directories are considered file stores.The java.nio.file.spi.FileSystemProvider class allows you to develop a custom file system provider
  • 32. Custom File System ProviderA custom file system provider is useful in the following situations Developing a memory-based or zip-file-based file system Developing a fault-tolerant distributed file system(Data Striping and Replication for high performace and to maintain data integrity) Replacing or supplementing the default file system provider(e.g. logging all system operations and delegate to the default provider for other routine operations)
  • 33. Custom File System ProviderImplementing Custom File System Provider Create a custom file system provider class that extends the java.nio.file.spi.FileSystemProvider class. Define a URI scheme (e.g file, jar, memory) for the file system provider. The getScheme method should return the URI scheme of this provider. Create an internal cache to keep track of file systems created by this provider. Implement the newFileSystem method. Implement the getFileSystem method. Implement the newFileChannel method or the newAsynchronousFileChannel method. This method should return a FileChannel object that allows a file to be read or written in the file system.
  • 34. Dynamic Language SupportNew Java bytecode "invokedynamic" has been addedAccompanying linkage mechanism that involves a new construct called a "Method Handle".Dynamic Language Compilers can use this new bytecodeDynamic Language should run faster on JVM
  • 35. Dynamic Language SupportWhat is "Dynamic Language" A class of high level programming language that execute at run time many common behaviours that static languages perform during compilation. Behaviour such as extension of the program by Adding new code Extending objects and definitions Modifying type sytem E.g Groovy, JRuby, Jython etc.
  • 36. Dynamic Language SupportThe Challenge of Compiling Dynamically Typed Languages Example to add two numbers def addtwo(a, b) a + b; endStatically Typed Language Compliler chooses implementation of "+" based on static types of a and b(iadd for integer)Dyanmically Typed Language Compiler must differ the choice until run time. The statement a + b is compiled as the method call +(a, b), where "+" is the method name The types of a and b will be determined at run time and accordingly the implementation of "+" will be called.
  • 37. Dynamic Language SupportCurrent Problem Bytecode instructions for Method invocation invokevirtual : Invokes a method on a class. invokeinterface - Invokes a method on an interface invokestatic - Invokes a static method on a class. invokespecial - Invokes a method without reference to the type of the receive e.g constructors, superclass methods or private methods.
  • 38. Dynamic Language SupportJava Code String s = "Hello World"; System.out.println(s);Bytecode ldc #2 // Push the String "Hello World" onto the stack astore_1 // Pop the value "Hello World" from the stack and store it in local variable #1 getstatic #3 // Get the static field java/lang/System.out:Ljava/io/PrintStream from the class aload_1 // Load the String referenced from local variable #1 invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  • 39. Dynamic Language SupportDifferent ways to handle Create language-specific Java types for the return value and method arguments, especially those which act as method call receivers Use java.lang.reflect.Method to invoke method Create a language-specific interpreter for method invocation to run on top of the JVM.
  • 40. Dynamic Language SupportInvokedynamic – New Bytecode instructionMethodHandle – Direct executable reference to an underlying method, constructor, field, or similar low-level operation, with optional transformations of arguments or return valuesCallSite – Holder for MethodHandle, which is called its target. An invokedynamic instruction linked to a CallSite delegates all calls to the sites current target.Bootstrap Method - This method links the name specified by the invokedynamic instruction with the code that should be executed (the target method), which is referenced by a method handle.
  • 41. Dynamic Language SupportThe invokedynamic instruction Simplifies and improves implementations of compilers and runtime systems for dynamic languages on the JVM Each instance of invokedynamic instruction is called a dynamic call site. A dynamic call site is originally in an unlinked state. i.e there is no method for call site to invoke. It is linked to a method by means of a bootstrap method Bootstrap method is specified by the compiler for the dynamically-typed language that is called once by the JVM to link the site The object returned from the bootstrap method permanently determines the call sites behavior
  • 42. Dynamic Language SupportExample IntegerOps class belongs to the library that accompanies the dynamic languages runtime system. The method Bootstrap.mybsm is a bootstrap method that links the invokedynamic call site to the adder method. The object callerClass is a lookup object, which is a factory for creating method handles. The method MethodHandles.Lookup.findStatic (called from the callerClass lookup object) creates a static method handle for the method adder.
  • 43. Dynamic Language SupportInvokedynamic bytecode
  • 44. The try-with-resources StatementIs a try statement that declares one or more resourcesA resource is as an object that must be closed after the program is finished with it.It ensures that each resource is closed at the end of the statement.Any object that implements java.lang.AutoCloseable can be used as a resource.E.gstatic String readFirstLineFromFile(String path) throws IOException {try (BufferedReader br = new BufferedReader(new FileReader(path))) { return br.readLine(); }}
  • 45. The try-with-resources StatementDeclaring multiple resourcestry ( java.util.zip.ZipFile zf = new java.util.zip.ZipFile(zipFileName); java.io.BufferedWriter writer = java.nio.file.Files.newBufferedWriter(outputFilePath, charset)){ //perform work } The close methods of resources are called in the oppositeorder of their creation.
  • 46. The try-with-resources StatementCan have catch and finally blocks just like an ordinary try statementAny catch or finally block is run after the resources declared have been closed
  • 47. The try-with-resources StatementSuppressed Exceptions An exception can be thrown from the block of code associated with the try-with-resources statement. In the example writeToFileZipFileContents, an exception can be thrown from the try block, and up to two exceptions can be thrown from the try-with-resources statement when it tries to close the ZipFile and BufferedWriter objects. Suppressed exceptions can be retrieved by calling the Throwable.getSuppressed method from the exception thrown by the try block.
  • 48. Improved Exception HandlingHanding more than one type of Exception Before Java 7 catch (IOException ex) { logger.log(ex); throw ex; catch (SQLException ex) { logger.log(ex); throw ex; } In Java 7 catch (IOException|SQLException ex) { logger.log(ex); throw ex; }
  • 49. Improved Exception HandlingRethrowing Exceptions with More Inclusive Type Checking Before Java 7 static class FirstException extends Exception { } static class SecondException extends Exception { } public void rethrowException(String exceptionName) throws Exception { try { if (exceptionName.equals("First")) { throw new FirstException(); } else { throw new SecondException(); } } catch (Exception e) { throw e; } }
  • 50. Improved Exception HandlingIn Java 7 public void rethrowException(String exceptionName) throws FirstException, SecondException { try { // ... } catch (Exception e) { throw e; } }
  • 51. Underscores in Numeric LiteralsAny number of underscore characters (_) can appear anywhere between digits in a numerical literal long creditCardNumber = 1234_5678_9012_3456L; long socialSecurityNumber = 999_99_9999L; float pi = 3.14_15F; long hexBytes = 0xFF_EC_DE_5E; long hexWords = 0xCAFE_BABE; long maxLong = 0x7fff_ffff_ffff_ffffL;
  • 52. Underscores in Numeric LiteralsAllowed only between digitsNot allowed At the beginning or end of a number Adjacent to a decimal point in a floating point literal Prior to an F or L suffix In positions where a string of digits is expected float pi1 = 3_.1415F; // Invalid; cannot put underscores adjacent to a decimal point float pi2 = 3._1415F; // Invalid; cannot put underscores adjacent to a decimal point int x1 = _52; // This is an identifier, not a numeric literal int x3 = 52_; // Invalid; cannot put underscores at the end of a literal
  • 53. String in switch StatementThe switch statement compares the String object using the String.equals methodConsequently the comparison is case sensitiveThe Java compiler generates generally more efficient bytecode from switch statements that use String objects than from chained if-then-else statements.
  • 54. Diamond Operator(<>)Type declaration is not required on right sideBefore Java 7 Map<String, List<Trade>> trades = new TreeMap<String, List<Trade>> ();In Java 7 Map<String, List<Trade>> trades = new TreeMap <> ();