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• Better to extend a class or modify it directly?

  - by primehunter326

  Hi, So I'm working on creating a visualization for a data structure in Java. I already have the implementation of the data structure (Binary Search Tree) to start with, but I need to add some additional functionality to the included node class. As far as conventions and best practices are concerned, should I create a subclass of the node with this added functionality or should I just modify what I have and document it there? My question is similar to what's asked here but that's a little over my head. I know it probably doesn't matter much for what I'm doing, so I'm asking this more as a general thing.

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• FileInputStream and FileOutputStream to the same file: Is a read() guaranteed to see all write()s that "happened before"?

  - by user946850

  I am using a file as a cache for big data. One thread writes to it sequentially, another thread reads it sequentially. Can I be sure that all data that has been written (by write()) in one thread can be read() from another thread, assuming a proper "happens-before" relationship in terms of the Java memory model? Is this behavior documented? EDIT: In my JDK, FileOutputSream does not override flush(), and OutputStream.flush() is empty. That's why I'm wondering... EDIT^2: The streams in question are owned exclusively by a class that I have full control of. Each stream is guaranteed to be accesses by one thread only. My tests show that it works as expected, but I'm still wondering if this is guaranteed and documented. See also this related discussion: http://chat.stackoverflow.com/rooms/17598/discussion-between-hussain-al-mutawa-and-user946850

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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• GWT: Loading different UI's based on URL

  - by jmccartie

  Trying to get a GWT project off the ground and finding it difficult to do any basic routing. Trying to fire up different UI's based on the URL. Thought I could set a string based on the getHash() and then switch off that, but seems cumbersome (and annoying since I can't do string-based switches in Java). There's got to be a best practice for this. I know Gerrit uses hashes for determining this type of information but couldn't find where they do it in the source. Or is this totally not GWT-related? Something I can handle in web.xml? Any help is much appreciated.

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• How should I be storing objects that I wish to access in reverse order of the way I placed them in

  - by andrew hicks

  I'm following this guide here: http://www.mazeworks.com/mazegen/mazetut/index.htm Or more specficially create a CellStack (LIFO) to hold a list of cell locations set TotalCells = number of cells in grid choose a cell at random and call it CurrentCell set VisitedCells = 1 while VisitedCells < TotalCells find all neighbors of CurrentCell with all walls intact if one or more found choose one at random knock down the wall between it and CurrentCell push CurrentCell location on the CellStack make the new cell CurrentCell add 1 to VisitedCells else pop the most recent cell entry off the CellStack make it CurrentCell endIf endWhile Im writing this in java, My problem is. How should I be storing my visited cells, So that I can access them from reverse order of when I placed them in. Like this? List<Location> visitedCells = new ArrayList<Location>(); Then do I grab with visitedCells.get(visitedCells.size()-1)? Location stores the x, y and z. Not something Im trying to ask you.

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• Solr adding document cycle & wait on response issue

  - by user1585896

  I am trying to send http post request to Solr for adding 50000 documents (all individual request one after another in while loop). I am using DefaultHttpClient in java to connect to Solr and when I use execute method on my HttpPost Solr takes 3 to 4 ms to response. I have commit=false, autoCommit=false, autoSoftCommit=false. My question is why it takes that much time to response and why cycle it follows to add new document. Basically I want to send add request but do not want to commit to see how many request can Solr handle without doing any kind of commits(without having to do any disk access). My guess is with above parameter tuned off I should be hitting Solr about 10000 times every second, but my result is 300 times a second. I am generating random data to add in my code.

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• Architect desperately wants to use SOAP over JMS

  - by Aerosteak

  Hello, I have used JMS in the past to build application and it works great. Now I work with Architects that would love to use the Spec : SOAP over Java Message Service 1.0. This spec seams overly complicated. I do not see many implementation (Beside the vendors pushing for the spec). Does anyone here is using this specification in a production environment? What is your main benefit of using this spec? Link: http://www.w3.org/TR/2009/CR-soapjms-20090604/

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• Hibernate entities stored as HttpSession attribute values

  - by njudge

  I'm dealing with a legacy Java application with a large, fairly messy codebase. There's a fairly standard 'User' object that gets stored in the HttpSession between requests, so the servlets do stuff like this at the top: HttpSession session = request.getSession(true); User user = (User)session.getAttribute("User"); The old user authentication layer (which I won't describe; suffice to say, it did not use a database) is being replaced with code mapped to the DB with Hibernate. So 'User' is now a Hibernate entity. My understanding of Hibernate object life cycles is a little fuzzy, but it seems like storing 'User' in the HttpSession now becomes a problem, because it will be retrieved in a different transaction during the next request. What is the right thing to be doing here? Can I just use the Hibernate Session object's update() method to reattach the User instance the next time around? Do I need to?

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• How can I make a recursive version of my iterative method?

  - by user247679

  Greetings. I am trying to write a recursive function in Java that prints the numbers one through n. (n being the parameter that you send the function.) An iterative solution is pretty straightforward: public static void printNumbers(int n){ for(int i = 1; i <= n; i++){ System.out.println(i); i++; } As a novice programmer, I'm having troubles figuring out how a recursive version of this method would work. Any bright ideas? Thanks for reading my problem!

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• How can I delete a specific element in priority queue?

  - by Yuan

  import java.util.*; public class test4 { public static void main(String[] args){ PriorityQueue[] P = new PriorityQueue[10]; P[1] = new PriorityQueue<ClassEntry>(); P[1].add(new ClassEntry(1.2,1)); P[1].add(new ClassEntry(1.5,2)); P[1].add(new ClassEntry(1.2,3)); P[1].add(new ClassEntry(10,4)); P[1].remove(new ClassEntry(10,4));//I can't delete this object??? System.out.println(P[1].size()); ClassEntry ce = (ClassEntry) P[1].peek(); System.out.println(P[1].size()); System.out.println(ce.sim+"\t"+ce.index); } } Why i can't delete (10,4)? Can somebody teach how to implement...thanks!

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• Parsing String to TreeNode

  - by Krusu70

  Anyone have a good algorithm how to parse a String to TreeNode in Java? Let's say we have a string s which says how to build a TreeNode. A(B,C) means that A is the name (String) of TreeNode, B is child of A (Treenode), C is sibling of A (TreeNode). So if I call function with string A(B(D,E(F,G)),C) (just a example), then I get a TreeNode equals to: level A (String: name), B - Child (TreeNode), C - Sibling (TreeNode) level B (String: name), D - Child of B (TreeNode), E - Sibling of B (TreeNode) level E (String: name), F - Child of E (TreeNode), G - Sibling of E (TreeNode) The name may not be 1 letter, it could be like real name (many letters).

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• How to test if an array contains a pair of numbers whose product is odd?

  - by John

  How can I write a function that takes an array of integers and returns true if their exists a pair of numbers whose product is odd? What are the properties of odd integers? And of course, how do you write this function in Java? Also, maybe a short explanation of how you went about formulating an algorithm for the actual implementation. Yes, this is a function out of a textbook. No, this is not homework—I'm just trying to learn, so please no "do your own homework comments."

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• Is there an automatic way to remove debugging methods for a release build?

  - by Lewis

  Note: This is an extension of an earlier question I asked here: Do additional function/method definitions increase a program's memory footprint? When I write a class, I usually end up writing several testing/debugging methods, used to make sure the class works as it should, or for printing data to help with debugging, or for unit testing, etc. Is there an easy/automatic way to make a release without these methods, or do I need to manually delete the extra code any time I want to compile a release version? I ask this question both from a C++ and a Java perspective. I'm using Code::Blocks and Eclipse as IDEs, if that plays into the answer somehow.

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• how to use a wav file in eclipse

  - by AlphaAndOmega

  I've been trying to add audio to a project I've been doing. I found some code on here for html that is also supposed to work with file but it keeps saying "Exception in thread "main" javax.sound.sampled.UnsupportedAudioFileException: could not get audio input stream from input file at javax.sound.sampled.AudioSystem.getAudioInputStream(Unknown Source) at LoopSound.main(LoopSound.java:15)" the code public class LoopSound { public static void main(String[] args) throws Throwable { File file = new File("c:\\Users\\rabidbun\\Pictures\\10177-m-001.wav"); Clip clip = AudioSystem.getClip(); // getAudioInputStream() also accepts a File or InputStream AudioInputStream wav = AudioSystem.getAudioInputStream( file ); clip.open(wav); // loop continuously clip.loop(-1000); SwingUtilities.invokeLater(new Runnable() { public void run() { // A GUI element to prevent the Clip's daemon Thread // from terminating at the end of the main() JOptionPane.showMessageDialog(null, "Close to exit!"); } }); } } What is wrong with the code?

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• Mixing HTML and STRUTS2 tags

  - by ryan

  I have a form which has both HMTL tags and struts tags. I use the HTML tags because of alignment issues with struts tags. <s:form action = "setNode" name = "processing" method ="POST"> <script> <!-- createTree(catArray); </script> <br/> <s:radio name="processOption" label="" list="{'Add','Move','Delete'}" ></s:radio> <s:textfield name="node" ></s:textfield> <s:submit name="Go" value=" Go " align="center" /> </s:form> the createTree function creates a tree form with HTML checkbox input types. The action triggers a java function. How do i see which checkboxes are checked?

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• Create a string with n characters.

  - by C. Ross

  Is there a way in java to create a string with a specified number of a specified character? In my case I would need to create a string with 10 spaces. My current code is: StringBuffer outputBuffer = new StringBuffer(length); for (int i = 0; i < length; i++){ outputBuffer.append(" "); } return outputBuffer.toString(); Is there a better way to accomplish the same thing. In particular I'd like something that is fast (in terms of execution).

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• JNAerator Unnamed Union Missing in Structure

  - by Nick

  I'm trying to get JNAerator to generate some JNA backed Java code from a C shared library and everything is fine except that it failed to generate an unnamed union nested inside a structure. Example: typedef struct MY_STRUCTURE { union { My_Type1 var1; My_Type2 var2; }; }MY_STRUCTURE; If I change the header to make the union have a name it will work. But for obvious reasons I can't just change the header without breaking the shared library I'm trying to use. Any solutions other than changing the header file and shared library to named union?

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• FTP - way to programatically determine time remaining or bytes transfered?

  - by ciaranarcher

  Hi all I want to make an FTP connection (ideally using Coldfusion 8, but Java is fine too) that will copy a file to a remote server. Crucially however, I want to know how many bytes have been transferred so I can give some feedback to the user. Is this possible, and if so what FTP API would you recommend as I understand the Sun implementation may be a bit lacking. Thanks in advance! PS: I could have another process/thread poll the file size on the destination machine via a web service call while the file is being transferred but it's not ideal. Getting it through FTP API would be the neatest solution.

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• [Java6] Same source code, Eclipse build success but Maven (javac) fails

  - by EnToutCas

  Keep getting this error when compiling using Maven: type parameters of <X>X cannot be determined; no unique maximal instance exists for type variable X with upper bounds int,java.lang.Object Generics type interference cannot be applied to primitive types. But I thought since Java5, boxing/unboxing mechanism works seamlessly between primitive types and wrapper classes. In any case, the strange thing is Eclipse doesn't report any errors and happily compiles. I'm using JDK1.6.0_12. What could possibly be the problem here?

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• When and why does an EventHandler require objects to be final?

  - by Michiel Borkent

  I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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• how do i close a frame yet open a new frame?(revisited)

  - by altvali

  I'm new at Java and I'm trying to do what the title says, my application has page A, a jpanel with some controls and a specific button, and when the user clicks the button i want page A to disappear and page B to appear (page B has controls that depend on the choices that are made by the user on page A). This has been asked before but there was no satisfactory answer. In the ActionListener implementation, namely public void ActionPerformed(ActionEvent e) from my jpanelForPageA class i can comfortably write this.setVisible(false), but how can i set page B to a visible state?

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• ask. help me to compare two array of integers and the order does not matter.

  - by stdnoit

  [Example] <1 2 3 4 = <3 1 2 4 <1 2 3 4 != <3 4 1 1 and ummm it is in java. cant use hashmap table or anything just pure without library. I know there are two ways. 1. sort them and compare the array index by index 2. use two for loops and compare the outer index with the inner index. ( i have been trying with this but still not working) for(int i = 0; i < n; i++) { for(int j = 0; j < n; j++) { if(a[i] != a[j] && j == n) return false; } } return true; anything wrong with the code ? thanks

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• How to export javascript generated report to pdf?

  - by Parhs

  Hello... I made a reporting engine with javascript for my project... The problem is with printing.. Although with page-break and css i can produce a good looking report, i want to export that report to a pdf in order to be printed better without ,the url,page title and other stuff that browsers add. Note in Chrome there isnt page setup!!! I am using java for server side. i think sending via ajax the Html of the report somehow and return a url for the pdf report maybe... i am looking for a good tool for this thank you

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• errorPage directive works, but error-page in web.xml doesn't?

  - by danb

  I get jsp exceptions causing a forward to my error page when I put this at the top of my JSPs... <%@ page errorPage="/error.page" %> but when I try to do it globally with web.xml like so: <error-page> <exception-type>java.lang.Throwable</exception-type> <location>/error.page</location> </error-page> I just get a blank page... I've also tried putting /error.jsp in the location element.. but no love with that either.. I am triggering an exception with a jsp that just contains this: <%if(true)throw new RuntimeException("test exception");%> I do see the exception in the console from tomcat but I just can't get that error page to show without a directive on every jsp... am I missing something simple here?

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• R.id cannot be resolved

  - by Soren

  So I copied this tutorial example thing right from Google's android site and I ma getting an error that R.id cannot be resolved. Here is my Java file package com.TestApp.HelloWebView; import android.app.Activity; import android.os.Bundle; import android.webkit.WebView; public class HelloWebView extends Activity { WebView mWebView; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mWebView = (WebView) findViewById(R.id.webview); mWebView.getSettings().setJavaScriptEnabled(true); mWebView.loadUrl("http://www.google.com"); } } Here is my main.xml <?xml version="1.0" encoding="utf-8"?> <WebView android:id="@+id/webview" android:layout_width="fill_parent" android:layout_height="fill_parent"/>

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