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• In Java What is the guaranteed way to get a FileLock from FileChannel while accessing a RandomAcces

  - by narasimha.bhat

  I am trying to use FileLock lock(long position, long size,boolean shared) in FileChannel object As per the javadoc it can throw OverlappingFileLockException. When I create a test program with 2 threads lock method seems to be waiting to acquire the lock (both exclusive and non exclusive) But when the number threads increases in the acutal scenario over lapping file lock exception is thrown and processing slows down due the block at File lock table. What is the best way to acquire lock avoiding the OverlappingFileLockException ?

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• Can Java ServerSocket and Sockets using ObjectIOStreams lose packets?

  - by Joel Garboden

  I'm using a ServerSocket on my server and Sockets that use ObjectIOStreams to send serializable objects over the network connection. I'm developing an essentially more financial version of monopoly and thus packets being sent and confirmed as sent/received is required. Do I need to implement my own packet loss watcher or is that already taken care of with (Server)Sockets? I'm primarily asking about losing packets during network blips or whatnot, not full connection error. E.g. siblings move a lead plate between my router and computer's wi-fi adapter. http://code.google.com/p/inequity/source/browse/#svn/trunk/src/network Code can be found under network-ClientController and network-Server

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• Help using Horner's rule and Hash Functions in JAVA?

  - by Matt

  I am trying to use Horner's rule to convert words to integers. I understand how it works and how if the word is long, it may cause an overflow. My ultimate goal is to use the converted integer in a hash function h(x)=x mod tableSize. My book suggests, because of the overflow, you could "apply the mod operator after computing each parenthesized expression in Horner's rule." I don't exactly understand what they mean by this. Say the expression looks like this: ((14*32+15)*32+20)*32+5 Do I take the mod tableSize after each parenthesized expression and add them together? What would it look like with this hash function and this example of Horner's rule?

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• How do I convert CamelCase into human-readable names in Java?

  - by Frederik

  I'd like to write a method that converts CamelCase into a human-readable name. Here's the test case: public void testSplitCamelCase() { assertEquals("lowercase", splitCamelCase("lowercase")); assertEquals("Class", splitCamelCase("Class")); assertEquals("My Class", splitCamelCase("MyClass")); assertEquals("HTML", splitCamelCase("HTML")); assertEquals("PDF Loader", splitCamelCase("PDFLoader")); assertEquals("A String", splitCamelCase("AString")); assertEquals("Simple XML Parser", splitCamelCase("SimpleXMLParser")); assertEquals("GL 11 Version", splitCamelCase("GL11Version")); }

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• Construct a SOAP Request to a WebService using Axis2 Library in Java?

  - by Ruchi Kaur

  Hello, I need to be able to construct a SOAP request using Apache Axis2 and provide the IP address and user agent in the SOAP header to the webservice. Is there a code sample that describes how to do that? Thanks in advance for the help! Best wishes Ruchi Kaur.

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• Why are local variables also called "Automatic" in Java?

  - by kunjaan

  I read this in Kathy Sierra's book: "Local variables are sometimes called stack, temporary, automatic, or method variables, but the rules for these variables are the same regardless of what you call them." Why are the local variables called automatic?

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• Java: illegal start of type error in try-catch-interface, why?

  - by HH

  The number of braces equals. What is the error for? static interface userInfo { File startingFile=new File("."); String startingPath="dummy"; try{ startingPath=startingFile.getCanonicalPath(); }catch(Exception e){e.printStackTrace();} } Error illegal start of type

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• How can I control the width of JTextFields in Java Swing?

  - by Jonas

  I am trying to have several JTextFields on a single row, but I don't want them to have the same width. How can I control the width and make some of them wider than others? I want that they together take up 100% of the total width, so it would be good if I could use some kind of weigthing. I have tried with .setColumns() but it doesn't make sense. Here is my code: class Row extends JComponent { public Row() { this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS)); JTextField fld1 = new JTextField("First field"); JTextField fld2 = new JTextField("Second field, should be longer"); JTextField fld3 = new JTextField("Short field"); JTextField fld4 = new JTextField("Another field"); fld1.setBorder(null); fld2.setBorder(null); fld3.setBorder(null); fld4.setBorder(null); fld1.setFocusable(false); fld2.setFocusable(false); fld3.setFocusable(false); fld4.setFocusable(false); fld1.setColumns(5); // makes no sense this.add(fld1); this.add(fld2); this.add(fld3); this.add(fld4); } } this.setLayout(new GridLayout(20,0)); this.add(new Row()); this.add(new Row()); this.add(new Row());

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• How do I create an ImageView in java code, within an existing Layout?

  - by Dan T

  I'm looking for an easy way for the user to see how many drinks they've had for a BAC calculator. PICTURE OF THE APP, for reference On button press, I would like an image to be added to the screen, directly under the spinner and with left alignment. When I press the button again, I want another image to be added to the screen. So if I pressed the add beer button, a drawable of a beer would appear below the spinner. If I pressed the add beer button again, I want there to be TWO drawables of beers under the spinner, preferably with them being added from the right. (Also, having them reach their width limit, wrapping around, and starting again on the left, but below a full line, would be AWESOME) I can't figure out how to do this. I assume adding a ImageView in code to a relative layout (because it needs to be positioned to the right) would be the best route, but if it's possible in xml I'd be more than happy to use that. Any help?

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• Is the Contains Method in java.lang.String Case-sensitive?

  - by Kamikaze Mercenary

  Say I have 2 strings, String s1 = "AbBaCca"; String s2 = "bac"; I want to preform a check returning that s2 is contained within s1. I can do this with: return s1.contains(s2); I am pretty sure that contains() is case sensitive, however I can't determine this for sure from reading the documentation. If it is then I suppose my best method would be something like: return s1.toLowerCase().contains(s2.toLowerCase()); All this aside, does anyone know of another (possibly better) way to accomplish this without caring about case-sensitivity?

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• How to indefinitely pause a thread in Java and later resume it?

  - by Carlos Torres

  Maybe this question has been asked many times before, but I never found a satisfying answer. The problem: I have to simulate a process scheduler, using the round robin strategy. I'm using threads to simulate processes and multiprogramming; everything works fine with the JVM managing the threads. But the thing is that now I want to have control of all the threads so that I can run each thread alone by a certain quantum (or time), just like real OS processes schedulers. What I'm thinking to do: I want have a list of all threads, as I iterate the list I want to execute each thread for their corresponding quantum, but as soon the time's up I want to pause that thread indefinitely until all threads in the list are executed and then when I reach the same thread again resume it and so on. The question: So is their a way, without using deprecated methods stop(), suspend(), or resume(), to have this control over threads?

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• Is checking for exceptions in code or using try-catch a better practice in Java?

  - by badpanda

  I had someone mention to me that catching all exceptions is not necessarily good practice (for example, NullPointerException). I am looking for an explanation of when this is a good thing, when it is not, and why it is as such :D Thanks!! badPanda

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• Java - How to avoid loss of precision during divide and cast to int?

  - by David Buckley

  I have a situation where I need to find out how many times an int goes into a decimal, but in certain cases, I'm losing precision. Here is the method: public int test(double decimalAmount, int divisor) { return (int) (decimalAmount/ (1d / divisor)); } The problem with this is if I pass in 1.2 as the decimal amount and 5 as the divisor, I get 5 instead of 6. How can I restrusture this so I know how many times 5 goes into the decimal amount as an int?

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• Spring-MVC Problem using @Controller on controller implementing an interface

  - by layne

  I'm using spring 2.5 and annotations to configure my spring-mvc web context. Unfortunately, I am unable to get the following to work. I'm not sure if this is a bug (seems like it) or if there is a basic misunderstanding on how the annotations and interface implementation subclassing works. For example, @Controller @RequestMapping("url-mapping-here") public class Foo { @RequestMapping(method=RequestMethod.GET) public void showForm() { ... } @RequestMapping(method=RequestMethod.POST) public String processForm() { ... } } works fine. When the context starts up, the urls this handler deals with are discovered, and everything works great. This however does not: @Controller @RequestMapping("url-mapping-here") public class Foo implements Bar { @RequestMapping(method=RequestMethod.GET) public void showForm() { ... } @RequestMapping(method=RequestMethod.POST) public String processForm() { ... } } When I try to pull up the url, I get the following nasty stack trace: javax.servlet.ServletException: No adapter for handler [com.shaneleopard.web.controller.RegistrationController@e973e3]: Does your handler implement a supported interface like Controller? org.springframework.web.servlet.DispatcherServlet.getHandlerAdapter(DispatcherServlet.java:1091) org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:874) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:809) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:571) org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:501) javax.servlet.http.HttpServlet.service(HttpServlet.java:627) However, if I change Bar to be an abstract superclass and have Foo extend it, then it works again. @Controller @RequestMapping("url-mapping-here") public class Foo extends Bar { @RequestMapping(method=RequestMethod.GET) public void showForm() { ... } @RequestMapping(method=RequestMethod.POST) public String processForm() { ... } } This seems like a bug. The @Controller annotation should be sufficient to mark this as a controller, and I should be able to implement one or more interfaces in my controller without having to do anything else. Any ideas?

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• Most Efficient Way of calling an external webservice in Java?

  - by Sudheer

  In one of our applications we need to call the Yahoo Soap Webservice to Get Weather and other related info. I used the wsdl2java tool from axis1.4 and generated th required stubs and wrote a client. I use jsp's use bean to include the client bean and call methods defined in the client which call the yahoo webservice inturn. Now the problem: When users make calls to the jsp the response time of the webservice differs greatly, like for one user it took less then 10 seconds and the other in the same network took more than a minute. I was just wondering if Axis1.4 queues the requests even though the jsps are multithreaded. And finally is there an efficient way of calling the webservice(Yahoo weather). Typically i get around 200 simultaneous requests from my users.

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• Please explain the hashCode of the java.lang.String.

  - by kunjaan

  What is the significance of the hashCode used inString? public int hashCode() { int h = hash; if (h == 0) { int off = offset; char val[] = value; int len = count; for (int i = 0; i < len; i++) { h = 31*h + val[off++]; } hash = h; } return h; }

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• How to read a password encrypted key with java?

  - by Denis

  Hi, This is very simple question. I have private key stored in file in PKCS8 DER format and protected by password. What is the easiest way to read it? Here is the code I use to load unencrypted one: InputStream in = new FileInputStream(privateKeyFilename); byte[] privateKeydata = new byte[in.available()]; in.read(privateKeydata); in.close(); KeyFactory privateKeyFactory = KeyFactory.getInstance("RSA"); PKCS8EncodedKeySpec encodedKeySpec = new PKCS8EncodedKeySpec(privateKeydata); PrivateKey privateKey = privateKeyFactory.generatePrivate(encodedKeySpec); Please, Help!!!

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• A simple free MIDI implementation in Java besides javax.sound.midi: Are there any?

  - by Peterdk

  The problem is: Android doesn't implement javax.sound.midi. I need a simple free library that allows me to create simple 1-track midi files. I searched the net for it, but can't really find anything, since everything uses javax.sound.midi . The license needs to be one where I don't need to opensource my linked app. Any ideas? I also looked into the fileformat itself. However, I am totally not familiar with working with bytes, hexidecimal stuff etc. So, other option is: are there any simple midi implementations that I can use as reference?

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• How does a Java Arraylist contains() method evalute objects?

  - by mvid

  Say i create one object and add it to my ArrayList. If I then create another object with exactly the same constructor input, will the contain() method evaluate the two objects to be the same? Assume the constructor doesn't do anything funny with the input, and the variables stored in both objects are identical. ArrayList<Thing> basket = new ArrayList<Thing>(); Thing thing = new Thing(100); basket.add(thing); Thing another = new Thing(100); basket.contains(another); // true or false?

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• Java InputReader. Detect if file being read is binary?

  - by Trizicus

  I had posted a question in regards to this code. I found that JTextArea does not support the binary type data that is loaded. So my new question is how can I go about detecting the 'bad' file and canceling the file I/O and telling the user that they need to select a new file? class Open extends SwingWorker<Void, String> { File file; JTextArea jta; Open(File file, JTextArea jta) { this.file = file; this.jta = jta; } @Override protected Void doInBackground() throws Exception { BufferedReader br = null; try { br = new BufferedReader(new FileReader(file)); String line = br.readLine(); while(line != null) { publish(line); line = br.readLine(); } } finally { try { br.close(); } catch (IOException e) { } } return null; } @Override protected void process(List<String> chunks) { for(String s : chunks) jta.append(s + "\n"); } }

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• how to create a static enum with a value that has a hypen symbol in java?

  - by coder

  Hi, how to create the static enum like below static enum Test{ employee-id, employeeCode } as of now, i am getting error.

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• Am I doing getters/setters the right way in Java?

  - by Sergio Tapia

  public class Persona { int Codigo; String Nombre; public Persona(int Codigo, String Nombre){ this.Codigo = Codigo; this.Nombre = Nombre; } public void setCodigo(int Codigo){ this.Codigo = Codigo; } public int getCodigo(){ return this.Codigo; } public void setNombre(String Nombre){ this.Nombre = Nombre; } public String getNombre(){ return this.Nombre; } } Or is there a much shorter (realiable) way to do it?

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• How to open word document with /m "Macro argument" from java/or command-line without to specifi winw

  - by Milan

  I want to do the next thing: String[] cmd = {"cmd","/c","c:\\Program Files (x86)\\Microsoft Office\\Office12\\WINWORD.exe","/mOpenPage","c:\\Navodilo.doc"}; Process proc = Runtime.getRuntime().exec(cmd); But, without to specify the winword.exe path... Ideas?

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• Private Java class properties mysteriously reset between method calls....

  - by Michael Jones

  I have a very odd problem. A class property is mysteriously reset between method calls. The following code is executed so the constructor is called, then the parseConfiguration method is called. Finally, processData is called. The parseConfiguration method sets the "recursive" property to "true". However, as soon as it enters "processData", "recursive" becomes "false". This problem isn't isolated to a single class -- I have several examples of this in my code. How can this possibly be happening? I've tried initialising properties when they're declared outside any methods, I've tried initialising them in constructors... nothing works. The only complication I can think of here is that this class is invoked by an object that runs in a thread -- but here is one instance per thread, so surely no chance that threads are interfering. I've tried setting both methods to "synchronized", but this still happens. Please help! /** * This class or its superclasses are NOT threaded and don't extend Thread */ public class DirectoryAcquirer extends Manipulator { /** * @var Whether to recursively scan directories */ private boolean recursive = false; /** * Constructor */ public DirectoryAcquirer() { } /** * Constructor that initialises the configuration * * @param config * @throws InvalidConfigurationException */ public DirectoryAcquirer(HierarchicalConfiguration config) throws InvalidConfigurationException { super(config); } @Override protected void parseConfiguration() throws InvalidConfigurationException { // set whether to recurse into directories or not if (this.config.containsKey("recursive")) { // this.recursive gets set to "true" here this.recursive = this.config.getBoolean("recursive"); } } @Override public EntityCollection processData(EntityCollection data) { // here this.recursive is "false" this.logger.debug("processData: Entered method"); } }

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• how to create a static enum with a value that has a hyphen symbol in java?

  - by coder

  Hi, how to create the static enum like below static enum Test{ employee-id, employeeCode } as of now, i am getting error.

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