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  • Ensuring all waiting threads complete

    - by Daniel
    I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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  • What to do when ServerSocket throws IOException

    - by s5804
    Basically I want to create a rock solid server. while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... } catch (IOException e) { e.printStackTrace(); // NOW WHAT? } } In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT); However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating.

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  • Has anyone tried the "objectify" library for Google App Engine?

    - by Spines
    I was using JDO for my google app engine project but got fed up with the additional 5 seconds it adds to my cold start time. I was planning on just writing stuff directly to the database with the low level datastore api, but then I came accross the objectify project ( http://code.google.com/p/objectify-appengine/ ). Apparently its a super light wrapper above the low level api. Does anyone have experiences with this library that they could share?

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  • pattern to transfer search model to dao

    - by zeroed
    We have a dao as a project (jar file). Clients use its interfaces and factories to operate with database. Using standard CRUD operations, dao allows you to search an entity by some search criteria. What is the best way to represent this criteria? Is transfer object appropriate pattern in this situation? How should client create SearchModel instance? Please, share. Regards.

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  • Hibernate database connection configuration

    - by Alvin
    We have 2 different server environments using the same Hibernate configuration. One server has JNDI support for datasource, but the other does not. Currently the Hibernate configuration is configured to use JNDI, which is causing problem on the server that does not support JNDI. I have also tried to put the direct JDBC configuration together with JNDI configuration into the configuration file, but it looks like hibernate always favors JNDI over direct JDBC configuration if both exist. My question is, will it be the same if both JNDI and connection_provider configuration both exists? Will Hibernate still use JNDI over connection_provider? Or is there any way to change the precedence of the database connection property? I do not have access to the server all the time, so I thought I do ask the question before my window of the sever time. Thanks in advance.

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  • Is there any point in using a volatile long?

    - by Adamski
    I occasionally use a volatile instance variable in cases where I have two threads reading from / writing to it and don't want the overhead (or potential deadlock risk) of taking out a lock; for example a timer thread periodically updating an int ID that is exposed as a getter on some class: public class MyClass { private volatile int id; public MyClass() { ScheduledExecutorService execService = Executors.newScheduledThreadPool(1); execService.scheduleAtFixedRate(new Runnable() { public void run() { ++id; } }, 0L, 30L, TimeUnit.SECONDS); } public int getId() { return id; } } My question: Given that the JLS only guarantees that 32-bit reads will be atomic is there any point in ever using a volatile long? (i.e. 64-bit). Caveat: Please do not reply saying that using volatile over synchronized is a case of pre-optimisation; I am well aware of how / when to use synchronized but there are cases where volatile is preferable. For example, when defining a Spring bean for use in a single-threaded application I tend to favour volatile instance variables, as there is no guarantee that the Spring context will initialise each bean's properties in the main thread.

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  • How to merge JOptionPane and Frame into one

    - by mike_hornbeck
    Hello. Currently I have a very basic file viewer working as follows : - in JOptionPane I browse for files, and set some variables to display (colors, line connecting etc) - previous windows loads a frame with drawn points Code : http://paste.pocoo.org/show/220066/ Now I'd like to throw it into one window, with JMenu for selecting files and changing display parameters. How to get started ? Should I rewrite everything to JDialog ?

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  • How to manipulate data after its retrieved via remote database

    - by bMon
    So I've used code examples from all over the net and got my app to accurately call a .php file on my server, retrieve the JSON data, then parse the data, and print it. The problem is that its just printing to the screen for sake of the tutorial I was following, but now I need to use that data in other places and need help figuring out that process. The ultimate goal is to return my db query with map coordinates, then plot them on a google map. I have another app in which I manually plot points on a map, so I'll be integrating this app with that once I can get my head around how to correctly manipulate the data returned. public class Remote extends Activity { /** Called when the activity is first created. */ TextView txt; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Create a crude view - this should really be set via the layout resources // but since its an example saves declaring them in the XML. LinearLayout rootLayout = new LinearLayout(getApplicationContext()); txt = new TextView(getApplicationContext()); rootLayout.addView(txt); setContentView(rootLayout); // Set the text and call the connect function. txt.setText("Connecting..."); //call the method to run the data retreival txt.setText(getServerData(KEY_121)); } public static final String KEY_121 = "http://example.com/mydbcall.php"; private String getServerData(String returnString) { InputStream is = null; String result = ""; //the year data to send //ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); //nameValuePairs.add(new BasicNameValuePair("year","1970")); try{ HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost(KEY_121); HttpResponse response = httpclient.execute(httppost); HttpEntity entity = response.getEntity(); is = entity.getContent(); }catch(Exception e){ Log.e("log_tag", "Error in http connection "+e.toString()); } //convert response to string try{ BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8); StringBuilder sb = new StringBuilder(); String line = null; while ((line = reader.readLine()) != null) { sb.append(line + "\n"); } is.close(); result=sb.toString(); }catch(Exception e){ Log.e("log_tag", "Error converting result "+e.toString()); } //parse json data try{ JSONArray jArray = new JSONArray(result); for(int i=0;i<jArray.length();i++){ JSONObject json_data = jArray.getJSONObject(i); Log.i("log_tag","longitude: "+json_data.getDouble("longitude")+ ", latitude: "+json_data.getDouble("latitude") ); //Get an output to the screen returnString += "\n\t" + jArray.getJSONObject(i); } }catch(JSONException e){ Log.e("log_tag", "Error parsing data "+e.toString()); } return returnString; } } So the code: returnString += "\n\t" + jArray.getJSONObject(i); is what is currently printing to the screen. What I have to figure out is how to get the data into something I can reference in other spots in the program, and access the individual elements ie: double longitude = jArray.getJSONObject(3).longitude; or something to that effect.. I figure the class getServerData will have to return a Array type or something? Any help is appreciated, thanks.

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  • Customizing TabWidget in SDK 1.5, API 3

    - by Dylan McClung
    I'm aware that API 3 doesn't allow a view to be set for a tab, but I still need to modify the TextView displayed as the indicator. I'd also like to change the Drawable for the tab, but I don't see a way to do it without a custom tab view as allowed in 1.6, API 4. Working with this generic example below, is there way to retrieve the TextView and modify its properties or change the drawable? TabHost tabHost = getTabHost(); TabHost.TabSpec spec; spec = tabHost.newTabSpec("nearby") .setIndicator("Nearby Activity") .setContent(R.id.nearby_list); tabHost.addTab(spec); spec = tabHost.newTabSpec("friends") .setIndicator("Friends & Favorites") .setContent(R.id.friends_list); tabHost.addTab(spec); tabHost.setCurrentTabByTag("nearby"); Thanks for any help.

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  • when get pagecontent from URL the connect alway return nopermistion ?

    - by tiendv
    I have a methor to return pagecontent of link but when it run, alway return "Do not perrmisson ", plesea check it here is code to return string pagecontent public static String getPageContent(String targetURL) throws Exception { Hashtable contentHash = new Hashtable(); URL url; URLConnection conn; // The data streams used to read from and write to the URL connection. DataOutputStream out; DataInputStream in; // String returned as the result . String returnString = ""; // Create the URL object and make a connection to it. url = new URL(targetURL); conn = url.openConnection(); // check out permission of acess URL if (conn.getPermission() != null) { returnString = "Do not Permission access URL "; } else { // Set connection parameters. We need to perform input and output, // so set both as true. conn.setDoInput(true); conn.setDoOutput(true); // Disable use of caches. conn.setUseCaches(false); // Set the content type we are POSTing. We impersonate it as // encoded form data conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // get the output stream . out = new DataOutputStream(conn.getOutputStream()); String content = ""; // Create a single String value pairs for all the keys // in the Hashtable passed to us. Enumeration e = contentHash.keys(); boolean first = true; while (e.hasMoreElements()) { // For each key and value pair in the hashtable Object key = e.nextElement(); Object value = contentHash.get(key); // If this is not the first key-value pair in the hashtable, // concantenate an "&" sign to the constructed String if (!first) content += "&"; // append to a single string. Encode the value portion content += (String) key + "=" + URLEncoder.encode((String) value); first = false; } // Write out the bytes of the content string to the stream. out.writeBytes(content); out.flush(); out.close(); // check if can't read from URL // Read input from the input stream. in = new DataInputStream(conn.getInputStream()); String str; while (null != ((str = in.readLine()))) { returnString += str + "\n"; } in.close(); } // return the string that was read. return returnString; }

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  • Bitmap size exceeds VM budget after second load

    - by jonny
    This is driving me crazy. I have a game which has a bitmap as the background, this is big so I scale it down and this works fine. However when I navigate to another activity and then reload the game screen it crashes on drawing the background. I am calling recycle on all the bitmaps and setting them to null on onDestroy() but this doesn't help. Any ideas and if not how can I debug the memory to see at which step its growing. I looked at getting the heap but nothing of any size is on there really. Thanks.

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  • Why new String(bytes, enc).getBytes(enc) does not return the original byte array?

    - by Bozho
    I made the following "simulation": byte[] b = new byte[256]; for (int i = 0; i < 256; i ++) { b[i] = (byte) (i - 128); } byte[] transformed = new String(b, "cp1251").getBytes("cp1251"); for (int i = 0; i < b.length; i ++) { if (b[i] != transformed[i]) { System.out.println("Wrong : " + i); } } For cp1251 this outputs only one wrong byte - at position 23. For KOI8-R - all fine. For cp1252 - 4 or 5 differences. What is the reason for this and how can this be overcome? I know it is wrong to represent byte arrays as strings in whatever encoding, but it is a requirement of the protocol of a payment provider, so I don't have a choice. Update: representing it in ISO-8859-1 works, and I'll use it for the byte[] part, and cp1251 for the textual part, so the question remains only out of curiousity

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  • install GlassFish on VPS

    - by ManWard
    hi i want install GlassFish into the VPS.now i need tutorial for installing GlassFish on VPS [Linux OS] and configure it.also how can i point separated domains to separated Web applications on Enterprise Server ? thanks

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  • problem in extending a class

    - by Vineeth
    there are two classes public class Account { public Acconut() { //constructor } } public class SavingsAccount extends Account { } while doing the inheritance i have got an error message "cannont find symbol Symbol: constructor Account()" what might be the error in my code...??

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  • Loading data from file to Vector structure

    - by owca
    I'm trying to parse through fixed-width formatted file extracting x,y values of points from it, and then storing them in int[] array inside a Vector. Text file looks as follows : 0006 0015 0125 0047 0250 0131 That's the code : Vector<int[]> vc = new Vector<int[]>(); try { BufferedReader file = new BufferedReader(new FileReader("myfile.txt")); String s; int[] vec = new int[2]; while ((s = file.readLine()) != null) { vec[0] = Integer.parseInt(s.substring(0, 4).trim()); vec[1] = Integer.parseInt(s.substring(5, 8).trim()); vc.add(vec); } file.close(); } catch (IOException e) { } for(int i=0; i<vc.size(); i++){ for(int j=0; j<2; j++){ System.out.println(vc.elementAt(i)[j]); } } But the output shows only last line. 250 131 250 131 250 131 Should I somehow use Vector.nextElement() here to get all my data ?

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  • Refining Solr searches, getting exact matches?

    - by thebluefox
    Afternoon chaps, Right, I'm constructing a fairly complex (to me anyway) search system for a website using Solr, although this question is quite simple I think... I have two search criteria, location and type. I want to return results that are exact matches to type (letter to letter, no exceptions), and like location. My current search query is as follows ../select/?q=location:N1 type:blue&rows=100&fl=*,score&debugQuery=true This firstly returns all the type blue's that match N1, but then returns any type that matches N1, which is opposite to what I'm after. Both fields are set as textgen in the Solr schema. Any pointers? Cheers gang

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  • Selecting multiple cached elements

    - by Globalz
    In jQuery you can select two elements by id like: $('#elem, #elem2'); BUT What if you have cached the elem and elem2, and what to apply the same method/function to them both? i.e. $elem = $('#elem'); $elem2 = $('#elem2'); This obviously wont work: $($elem, $elem2) Thanks!

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  • How Netbeans Editors know that file is not modified after undo?

    - by Ha
    Netbeans uses standart UndoManager API for implementation of undo functionality. But neither standart javax.swing.undo.UndoManager nor org.openide.awt.UndoRedo.Manager doesn't have any method to mark states as saved and check modified status. Nonetheless if you change the file and press undo, the file is marked as unmodified. How do they do that? I need the same functionality for my (non-text) editors if the Netbeans RCP application.

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  • JMenu issue with Gnome's native look and feel.

    - by gmunk
    I stumbled on a very odd problem while trying to set up a JMenuBar with the native look and feel of Gnome. Here is a screenshot: http://img23.imageshack.us/i/issuel.png/ It has to say File there but it gets cut out. http://pastebin.com/CjFhmxcf http://pastebin.com/gwB3vnC3 Any, help is appreciated!

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  • Find the gender from a name

    - by Ramesh
    Hi guys, I recently confronted with a weird yet interesting question. The questions is as follows: Need to write a program which can give the gender as output based on the name. Example: INPUT -- John Michael Britney OUTPUT-- male male female So this is the output I expect. I tried a lot to solve, but I really was not able to crack it. I will be really thankful to this site for giving me an opportunity to share this question. Actually this is asked in a programming contest as a flyer problem, so I thought this can be programmed.

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