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• Understanding character encoding in typical Java web app

  - by Marcus

  Some pseudocode from a typical web app: String a = "A bunch of text"; //UTF-16 saveTextInDb(a); //Write to Oracle VARCHAR(15) column String b = readTextFromDb(); //UTF-16 out.write(b); //Write to http response In the first line we create a Java String which uses UTF-16. When you save to Oracle VARCHAR(15) does Oracle also store this as UTF-16? Does the length of an Oracle VARCHAR refer to number of Unicode characters (and not number of bytes)? And then when we write b to the ServletResponse is this being written as UTF-16 or are we by default converting to another encoding like UTF-8?

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• How to rate a connect four game situation in java

  - by MrPink

  Hey, I am trying to write a simple AI for a "Get four" game. The basic game principles are done, so I can throw in coins of different color, and they stack on each other and fill a 2D Array and so on and so forth. until now this is what the method looks like: public int insert(int x, int color) //0 = empty, 1=player1 2=player2" X is the horizontal coordinate, as the y coordinate is determined by how many stones are in the array already, I think the idea is obvious. Now the problem is I have to rate specific game situations, so find how many new pairs, triplets and possible 4 in a row I can get in a specific situation to then give each situation a specific value. With these values I can setup a "Game tree" to then decide which move would be best next (later on implementing Alpha-Beta-Pruning). My current problem is that I can't think of an efficient way to implement a rating of the current game situation in a java method. Any ideas would be greatly appreciated! greetings from Germany Mr. Pink

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• Clean way in GWT/Java to wait for multiple asynchronous events to finish

  - by gerdemb

  What is the best way to wait for multiple asynchronous callback functions to finish in Java before continuing. Specifically I'm using GWT with AsyncCallback, but I think this is a generic problem. Here's what I have now, but surely there is cleaner way... AjaxLoader.loadApi("books", "0", new Runnable(){ public void run() { bookAPIAvailable = true; ready(); }}, null); AjaxLoader.loadApi("search", "1", new Runnable(){ public void run() { searchAPIAvailable = true; ready(); }}, null); loginService.login(GWT.getHostPageBaseURL(), new AsyncCallback<LoginInfo>() { public void onSuccess(LoginInfo result) { appLoaded = true; ready(); } }); private void ready() { if(bookAPIAvailable && searchAPIAvailable && appLoaded) { // Everything loaded } }

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• Perl launched from Java takes forever

  - by Wade Williams

  I know this is an absolute shot in the dark, but we're absolutely perplexed. A perl (5.8.6) script run by Java (1.5) is taking more than an hour to complete. The same script, when run manually from the command line takes 12 minutes to complete. This is on a Linux host. Logging is the same in both cases and the script is run with the same parameters in both cases. The script does some complex stuff like Oracle DB access, some scp's, etc, but again, it does the exact same actions in both cases. We're stumped. Has anyone ever run into a similar situation? If not and if you were faced with the same situation, how would you consider debugging it?

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• Global Exception Handlers in Java

  - by Samuh

  I am thinking of setting up a global, default Exception handler for my (Android) Mobile application(which uses Java syntax) using Thread.setDefaultUncaughtExceptionHandler(...) call. I am thinking of just displaying an Alert Dialog with appropriate message to the user. Are there any gotchas, caveats and rules that one needs to follow when setting DefaultExceptionHandlers? Any best practices like making sure that the process is killed, full stack trace is written to logs etc. ? Links to documentation, tutorials etc. that can throw some light on this are welcome. Thanks.

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• Send custom data when initializing java WebService over soap

  - by Mesni

  Hello. I have a question about sending additional data over soap to the functions. My webService function requests only one integer, for example an getDocumentPrivilage(DocumentID). In another WebService user registered and he got an unique ID, so the other application can see who he is. So on Service one he registers, gets id and it has to send it to the other webservice tor the privilage. Id dont wish to rewrite the function so that it gets the unique ID (like this getDocumentPrivilage(uniqID,DocumentID)) but, the wish is that i would be able to create a client that sends this data at the initialization or somehow as some sort of parameter behind the function. Is this possible?? I tried the ServiceLifecycle but cant see any setting i've given in. Im using WebSphere CE for the server and Jax-ws Creating the webapp in java. Thank you very much in advance. lp, Mesni

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• Java reduce CPU usage

  - by steve

  Greets- We gots a few nutters in work who enjoy using while(true) { //Code } in their code. As you can imagine this maxes out the CPU. Does anyone know ways to reduce the CPU utilization so that other people can use the server as well. The code itself is just constantly polling the internet for updates on sites. Therefore I'd imagine a little sleep method would greatly reduce the the CPU usage. Also all manipulation is being done in String objects (Java) anyone know how much StringBuilders would reduce the over head by? Thanks for any pointers

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• Create instance of generic type in Java?

  - by David Citron

  Is it possible to create an instance of a generic type in Java? I'm thinking based on what I've seen that the answer is "no" (due to type erasure), but I'd be interested if anyone can see something I'm missing: class SomeContainer<E> { E createContents() { return what??? } } EDIT: It turns out that Super Type Tokens could be used to resolve my issue, but it requires a lot of reflection-based code, as some of the answers below have indicated. I'll leave this open for a little while to see if anyone comes up with anything dramatically different than Ian Robertson's Artima Article.

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• Java: how to represent graphs?

  - by Rosarch

  I'm implementing some algorithms to teach myself about graphs and how to work with them. What would you recommend is the best way to do that in Java? I was thinking something like this: public class Vertex { private ArrayList<Vertex> outnodes; //Adjacency list. if I wanted to support edge weight, this would be a hash map. //methods to manipulate outnodes } public class Graph { private ArrayList<Vertex> nodes; //algorithms on graphs } But I basically just made this up. Is there a better way? Also, I want it to be able to support variations on vanilla graphs like digraphs, weighted edges, multigraphs, etc.

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• Java String to SHA1

  - by AeroDroid

  I'm trying to make a simple String to SHA1 converter in Java and this is what I've got... public static String toSHA1(byte[] convertme) { MessageDigest md = null; try { md = MessageDigest.getInstance("SHA-1"); } catch(NoSuchAlgorithmException e) { e.printStackTrace(); } return new String(md.digest(convertme)); } When I pass it toSHA1("password".getBytes()), I get "[?a?????%l?3~??." I know it's probably a simple encoding fix like UTF-8, but could someone tell me what I should do to get what I want which is "5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8"? Or am I doing this completely wrong? Thanks a lot!

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• Java: PriorityQueue returning incorrect ordering from custom comparator??

  - by Michael Simpson

  I've written a custom comparator to compare my node classes, but the java priority queue is not returning my items in the correct order. Here is my comparator: public int compare(Node n1, Node n2){ if (n1.getF() > n2.getF()){ return +1; } else if (n1.getF() < n2.getF()){ return -1; } else { // equal return 0; } } Where getF returns a double. However after inserting several Nodes into the priority queue, I print them out using: while(open.size() > 0) { Node t = (Node)(open.remove()); System.out.println(t.getF()); } Which results in: 6.830951894845301 6.830951894845301 6.0 6.0 5.242640687119285 7.4031242374328485 7.4031242374328485 8.071067811865476 Any ideas why this is so? Is my comparator wrong? Thanks. Mike

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• Fast way to pass a simple java object from one thread to another

  - by Adal

  I have a callback which receives an object. I make a copy of this object, and I must pass it on to another thread for further processing. It's very important for the callback to return as fast as possible. Ideally, the callback will write the copy to some sort of lock-free container. I only have the callback called from a single thread and one processing thread. I only need to pass a bunch of doubles to the other thread, and I know the maximum number of doubles (around 40). Any ideas? I'm not very familiar with Java, so I don't know the usual ways to pass stuff between threads.

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• Can I add and remove elements of enumeration at runtime in Java

  - by Brabster

  It is possible to add and remove elements from an enum in Java at runtime? For example, could I read in the labels and constructor arguments of an enum from a file? @saua, it's just a question of whether it can be done out of interest really. I was hoping there'd be some neat way of altering the running bytecode, maybe using BCEL or something. I've also followed up with this question because I realised I wasn't totally sure when an enum should be used. I'm pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.

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• Java: pass an event to another component

  - by John

  Sorry I don't know if this is very clear, but I'm pretty new to Java. So I have a JFrame with a BorderLayout containing a JPanel and a JButton. What I want to do is when something happens in my JPanel, I want for example change the text of the JButton, or enable/disable it. How would I do that? How can I access the JButton from the JPanel? I know some ways of doing it but I don't think they're the best way to do it. What would be the best way to do this? Thanks in advance

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• Examples of both beautiful and ugly java code?

  - by tputkonen

  I would like to demonstrate how difficult it is for a layman to identify high quality code from flawed code. I'm thinking of doing this with the help of two java methods. Both of the methods should look like they do the same, pretty simple thing. However one of them should have several kind of flaws, for example: iteration with array off by one error string concatenations causing lots of objects to be created (as opposed to StringBuffer in the "good" code, which looks more complicated) possibly null pointer exception (but it should not be trivial to spot) Those are just some examples, all kinds of other issues including bugs and performance related structures are highly appreciated. Methods should be around 10-20 lines of length, and the task they do should be something simple - preferably printing something in an iteration.

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• when to use StringBuilder in java

  - by kostja

  It is supposed to be generally preferable to use a StringBuilder for String concatenation in Java. Is it always the case? What i mean is : Is the overhead of creating a StringBuilder object, calling the append() method and finally toString() smaller then concatenating existing Strings with + for 2 Strings already or is it only advisable for more Strings? If there is such a threshold, what does it depend on (the String length i suppose, but in which way)? And finally - would you trade the readability and conciseness of the + concatenation for the performance of the StringBuilder in smaller cases like 2, 3, 4 Strings?

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• java.lang.OutOfMemoryError: unable to create new native thread for multiple threads

  - by Kaustubh Ranjan Singh

  static class solver implements Runnable { static calculator(problem){ //Some code if(condition) {solver s = new solver(newproblem); new Thread(s).start();} } Public solver(int newproblem) { this.problem = newproblem ; } public void run() { // TODO Auto-generated method stub calculator(promblem); } } i am having a big array maze of 100x100 and i am trying to solve it and i am getting an error java.lang.OutOfMemoryError: unable to create new native thread(after running a code for some times). How can solve this , How can i use ExecutorService i think that will solve the problem or i want something like thisIf Number of generated threads4K then stop the first 100 threads

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• Sort Java List/Map by order in which items are in an XML File

  - by Brandon Smith

  Hello everyone, What I'm looking to do is to sorta a Java List or Map in the order the items are in a XML File. For Example I have a list of function names as so: functionOne functionThree functionTwo The XML File looks like this: <xml> <function>functionOne</function> <function>functionTwo</function> <function>functionThree</function> </xml> So I would like to sort the list so the function names are as so: functionOne functionTwo functionThree Now Im trying to do this for Variables as well, so there are around 500+ unique 'items'. Does anyone have any idea how I can go about doing this? Now for the file that determines that sort order doesn't have to be XML it just what I use the most, it can be anything that can get the job done. Thanks in advance for your time.

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• Java multidimensional array and scanner novice Q

  - by Max

  I'm new to Java and trying to in essence implement a grid with a character, and if the user inputs 'w' 'a' 's' or 'd' the character moves up/down/left/right within the plane. I created a multidimensional array sized 10x10 public static String[][] grid = new String[10][10]; And then just used a for loop to print "*"s in a 10x10 grid, except for grid[a][b] which is equal to character "A" i.e. my thing to be moved around. That seemed to work alright, then I needed to detect the 'wasd' input from the user so I set up a: Scanner in = new Scanner (System.in); while (in.hasNext()) And I had then: String s = in.next(); char ch = s.charAt(0); switch (ch) but I couldn't make this work, and it wasn't because I didn't complete the "switch" statement, I did, I just see it void copying and pasting the entire thing. I'm sure its incredibly easy slight thing I am missing, can you please point it out for me?

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• generating function arguments in java

  - by aloishis89

  I'm very new to java and am working on my first Android app. I am using the webview demo as a template. I am trying to generate a random integer between 1 and 12 and then call a certain javascript function based on the result. Here's what I have: int number = 1 + (int)(Math.random() * ((12 - 1) + 1)); number = (int) Math.floor(number); String nextQuote = "javascript:wave" + number + "()"; mWebView.loadUrl(nextQuote); So mWebView.loadUrl(nextQuote) will be the same as something like mWebView.loadUrl("javascript:wave1()") I just want to know if what I have here is correct and will work the way I think it will. The application isn't responding as expected and I suspect this bit of code is the culprit.

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• Java - Reg. Ex. File Question

  - by aloh

  I'm grabbing lines from a text file and sifting line by line using regular expressions. I'm trying to search for blank lines, meaning nothing or just whitespace. However, what exactly is empty space? I know that whitespace is \s but what is a line that is nothing at all? null (\0)? newline (\n)? I tried the test harness in the Java tutorial to try and test to see what an empty space is but no luck so far.

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• how to get a constant in java with class

  - by vincent

  basically I need to get a constant for a class however I have no instance of the object but only its class. In PHP I would do constant(XYZ); Is there a similar way of retrieving a constant in JAVA? I need it to facilitate a dynamic getMethod call Class parameterType = Class.forName(class_name); object.setProperty(field name, field value, parameterType); the set property method would then get the correct method and set the specified property, however I cant get a method which has int as parameter type without using Interger.TYPE

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• Convert php to java/android arrays

  - by lacas

  $tagArray = array( "apples" => 12, "oranges" => 38, "pears" => 10, "mangos" => 24, "grapes" => 18, "bananas" => 56, "watermelons" => 80, "lemons" => 12, "limes" => 12, "pineapples" => 15, "strawberries" => 20, "coconuts" => 43, "cherries" => 20, "raspberries" => 8, "peaches" => 25 ); and how i can do this in java, and how to calling for the first and second params?

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• Java Synchronized Write Block

  - by ikurtz

  im new to java and i have a question regarding Synchronized. i have the following code for writing to network (simple implementation for now): public void networkSendData(byte[] data){ try { out.write(data); out.flush(); } catch (IOException e) { } } i was wondering if there is a need for block level Synchronized here as im am writing the whole data at once. or is there a chance for race condition? i ask because the data to write is coming for multiple sources. thank you.

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• Count in base 2, 3, 4 etc in Java and output all permutations

  - by tree-hacker

  I want to write a function in Java that takes as input an integer and outputs every possible permutation of numbers up to that integer. For example: f(1) 0 f(2) should output: 00 01 10 11 f(3) should output: 000 001 002 010 011 012 020 021 022 100 .... 220 221 222 That is it should output all 27 permutations of the digits of the numbers 0, 1, 2. f(4) should output 0000 0001 0002 0003 0010 ... 3330 3331 3332 3333 f(4) should output 00000 00001 ... 44443 44444 I have been trying to solve this problem but cannot seem to work out how to do it and keep getting confused by how many loops I need. Does anyone know how to solve this problem? Thanks in advance.

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