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  • How to access java collection, just like the table in the database, having indexes and LINQ-like que

    - by Shaman
    This task occurs from time to time in my projects. I need to handle a collection of some complex elements, having different attributes, such as login, password_hash, role, etc. And, I need to be able to query that collection, just like I query a table in the database, having only partial data. For example: get all users, with role "user". Or check, if there's a user with login "root" and role "superuser". Removing items, based on same data is also needed. The first attempt I've tried is to use Google collections, Apache collections, and lambdaj. All of them have very similar preicate mechanism, but with a great disadvantage: it is based on iteration, one by one, over the collection of items, which is not good, for often used collections, containing big amounts of data. Could you please suggest me some solution? Thanks.

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  • Auto-size zoom on Google Maps in java? (depending android screen resolution)

    - by poeschlorn
    Hey guys, i've got 2 GeoPoints given to show them on the map with markers... so far so good... how can I get the optimum zoom level for the MapController in order to focus the middle of both points, but also have them on the map. The whole thing should work at different screen resolutions. Sorry for asking that silly question, I know thats not very difficult, but at the moment my head is boiling :/

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  • How is this statement making sense? (Sun's naming convention for Java variables)

    - by polygenelubricants
    I've been quoting this segment from Sun's document for the past few days, and only now do I stop and think about what it's saying, and I can't make sense out of it. Please keep in mind that English is not my first language. Naming conventions Variables: Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. How is this making sense? Isn't this saying that class names are in mixed case with a lowercase first letter? Like I should name it class myClass? And class constants are also in mixed case with a lowercase first letter? Like I should name it Integer.maxValue? And is it really saying anything about how variables themselves should be named? Am I not parsing this properly or is this actually a blatant error?

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  • Playing around with my Java project in Eclipse... what the crap did I just do?

    - by Daddy Warbox
    I don't even remember how, but somehow I managed to make all of my project's source files hidden in Eclipse's Package and Project Explorer panels. Go figure. 'Show Filtered Children (alt+click)' temporarily reveals the files, and only in Package Explorer can I double-click to reopen them from this view. They go back into hiding after I select another item, though. Plus, now I'm getting other annoyances, such as all of the folded non-hidden items altogether expanding when I click on an item, and the entire folder tree of my project now being shown in these panels (including my .svn subversion folders... which shouldn't be any of Eclipse's business, presently). Long story short, my Package/Project Explorers' just blew up on me, and I want to know how to fix this. Thanks in advance. P.S. What's a good guide I can use to learn my way around this silly contraption, anyway?

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  • Java Graphics not displaying on successive function calls, why?

    - by primehunter326
    Hi, I'm making a visualization for a BST implementation (I posted another question about it the other day). I've created a GUI which displays the viewing area and buttons. I've added code to the BST implementation to recursively traverse the tree, the function takes in coordinates along with the Graphics object which are initially passed in by the main GUI class. My idea was that I'd just have this function re-draw the tree after every update (add, delete, etc...), drawing a rectangle over everything first to "refresh" the viewing area. This also means I could alter the BST implementation (i.e by adding a balance operation) and it wouldn't affect the visualization. The issue I'm having is that the draw function only works the first time it is called, after that it doesn't display anything. I guess I don't fully understand how the Graphics object works since it doesn't behave the way I'd expect it to when getting passed/called from different functions. I know the getGraphics function has something to do with it. Relevant code: private void draw(){ Graphics g = vPanel.getGraphics(); tree.drawTree(g,ORIGIN,ORIGIN); } vPanel is what I'm drawing on private void drawTree(Graphics g, BinaryNode<AnyType> n, int x, int y){ if( n != null ){ drawTree(g, n.left, x-10,y+10 ); if(n.selected){ g.setColor(Color.blue); } else{ g.setColor(Color.gray); } g.fillOval(x,y,20,20); g.setColor(Color.black); g.drawString(n.element.toString(),x,y); drawTree(g,n.right, x+10,y+10); } } It is passed the root node when it is called by the public function. Do I have to have: Graphics g = vPanel.getGraphics(); ...within the drawTree function? This doesn't make sense!! Thanks for your help.

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  • How to display an icon on JOptionPane.showInputDialog() in Java?

    - by Lion
    The following segment of code shows JOptionPane.showInputDialog() method. It works fine but I need to display a custom icon on it. I currently left it null as shown below. String operatingSystem = System.getProperty("os.name"); Object o[] = {"Turn Off", "Restart", "Stand By", "Log Off"}; Frame frame = new Frame(operatingSystem); Object selectedValue = JOptionPane.showInputDialog(frame, "What would you like to do with the system?", "Select a task", JOptionPane.INFORMATION_MESSAGE, null, o, o[0]); //<---- Here it is. How can an icon be displayed on it replacing null?

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  • How to get the line number an xml element is on via the Java w3c dom api

    - by Benju
    Is there a way to lookup the line number that a given element is at in an xml file via the w3c dom api? My use case for this is that we have 30,000+ maps in kml/xml format. I wrote a unit test that iterates over each file found on the hard drive (about 17GB worth) and tests that it is parseable by our application. When it fails I throw an exception that contains the element instance that was considered "invalid". In order for our mapping department (nobody here knows how to program) to easily track down the typo we would like to log the line number of the element that caused the exception. Can anybody suggest a way to do this? Please note we are using the W3C dom api included in the Android 1.6 SDK.

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  • Using an interface as a constructor parameter in Java?

    - by aperson
    How would I be able to accomplish the following: public class testClass implements Interface { public testClass(Interface[] args) { } } So that I could declare Interface testObject = new testClass(new class1(4), new class2(5)); Where class1 and class2 are also classes that implement Interface. Also, once I accomplish this, how would I be able to refer to each individual parameter taken in to be used in testClass? Thanks :)

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  • How to generate a random BigInteger value in Java?

    - by Bill the Lizard
    I need to generate arbitrarily large random integers in the range 0 (inclusive) to n (exclusive). My initial thought was to call nextDouble and multiply by n, but once n gets to be larger than 253, the results would no longer be uniformly distributed. BigInteger has the following constructor available: public BigInteger(int numBits, Random rnd) Constructs a randomly generated BigInteger, uniformly distributed over the range 0 to (2numBits - 1), inclusive. How can this be used to get a random value in the range 0 - n, where n is not a power of 2?

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  • How to kill a thread immediately from another thread in java?

    - by Sara
    Hi, is there anyway to kill a thread or interrupt it immediately. Like in one of my thread, i call a method which takes time to execute (2-4 seconds). This method is in a while(boolean flag) block, so i can interrupt it from the main thread. But the problem is, if i interrupt it; it will wait till the executing loop is finished and then on next conditional check, it will stop execution. I want it to stop right then. Is there anyway to do this?

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  • Java: Allowing the child thread to kill itself on InterruptedException?

    - by Zombies
    I am using a ThreadPool via ExecutorService. By calling shutDownNow() it interrupts all running threads in the pool. When this happens I want these threads to give up their resources (socket and db connections) and simply die, but without continuing to run anymore logic, eg: inserting anything into the DB. What is the simplest way to achieve this? Bellow is some sample code: public void threadTest() { Thread t = new Thread(new Runnable() { public void run() { try { Thread.sleep(999999); } catch (InterruptedException e) { //invoke thread suicide logic here } } }); t.start(); t.interrupt(); try { Thread.sleep(4000); } catch (InterruptedException e) { } }

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  • Java me : Can we retrieve bluetooth address of connected device from an open slave connection ?

    - by Rohit
    Here is a typical sequence of events that occur : Host device opens a service ( Host device accepts and opens all incoming connections) A remote device connects to host device. Now, we have a slave connection open at host device. At host device, I want to know the bluetooth address of remote device. I can always pass it as data from remote to host device, but can I extract it from connection object somehow without any data transfer? Thanks in advance...

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  • What's my best approach on this simple hierarchy Java Problem?

    - by Nazgulled
    First, I'm sorry for the question title but I can't think of a better one to describe my problem. Feel free to change it :) Let's say I have this abstract class Box which implements a couple of constructors, methods and whatever on some private variables. Then I have a couple of sub classes like BoxA and BoxB. Both of these implement extra things. Now I have another abstract class Shape and a few sub classes like Square and Circle. For both BoxA and BoxB I need to have a list of Shape objects but I need to make sure that only Square objects go into BoxA's list and only Circle objects go into BoxB's list. For that list (on each box), I need to have a get() and set() method and also a addShape() and removeShape() methods. Another important thing to know is that for each box created, either BoxA or BoxB, each respectively Shape list is exactly the same. Let's say I create a list of Square's named ls and two BoxA objects named boxA1 and boxA2. No matter what, both boxA1 and boxA2 must have the same ls list. This is my idea: public abstract class Box { // private instance variables public Box() { // constructor stuff } // public instance methods } public class BoxA extends Box { // private instance variables private static List<Shape> list; public BoxA() { // constructor stuff } // public instance methods public static List<Square> getList() { List<Square> aux = new ArrayList<Square>(); for(Square s : list.values()) { aux.add(s.clone()); // I know what I'm doing with this clone, don't worry about it } return aux; } public static void setList(List<Square> newList) { list = new ArrayList<Square>(newList); } public static void addShape(Square s) { list.add(s); } public static void removeShape(Square s) { list.remove(list.indexOf(s)); } } As the list needs to be the same for that type of object, I declared as static and all methods that work with that list are also static. Now, for BoxB the class would be almost the same regarding the list stuff. I would only replace Square by Triangle and the problem was solved. So, for each BoxA object created, the list would be only one and the same for each BoxB object created, but a different type of list of course. So, what's my problem you ask? Well, I don't like the code... The getList(), setList(), addShape() and removeShape() methods are basically repeated for BoxA and BoxB, only the type of the objects that the list will hold is different. I can't think of way to do it in the super class Box instead. Doing it statically too, using Shape instead of Square and Triangle, wouldn't work because the list would be only one and I need it to be only one but for each sub class of Box. How could I do this differently and better? P.S: I could not describe my real example because I don't know the correct words in English for the stuff I'm doing, so I just used a box and shapes example, but it's basically the same.

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  • Analysing objects generated by a Java application in between GCs.

    - by elec
    Is there a tool which could be used to analyse the objects being created between two separate garbage collection run (= number of objects created and their type) ? Heapdumps dont really work here as they perform a GC when they're invoked (or at least that's what I observed everytime so far), and I want to see which objects are collected by the GC, not which objects are left after the GC run, if that makes sense. ...or is it possible somehow to inspect the nature and size of objects being collected by the garbage collector ?

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  • Java, How to Instance HttpCookie from a String, any convenient ways?

    - by user435657
    Hi all, I have got a cookie string from HTTP response header like the following line: name=value; path=/; domain=.g.cn; expire=... I can parse the above line to key-value pairs, and, also it's easy to set the name and value to HttpCookie instance as this pair comes the first. But how to set the other pairs since I don't know which set-method corresponds to the name of the next name-value pair. Traverse all possible keys a cookie may contian and call the matched set-method, like below snippet? if (key.equalsIgnoreCase("path")) cookie.setPath(value); else if (key.equalsIgnoreCase("domain")) cookie.setDomain(value); That's foolish, any convenient ways? Thanks in advance.

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  • My java program seems to be skipping over the try{}, executing the catch{} and then throwing a NullPointerException. What should I do?

    - by Matt Bolopue
    I am writing a program that calculates the number of words, syllables, and sentences in any given text file. I don't need help finding those numbers, however my program (which currently should only find the number of words in the text file) will not import the text file even when I type in the name of the file correctly. The text file is in the same folder as the source code. Instead it tells me every time that what I typed in has the wrong file extension (see my catch{}) and then proceeds to throw a null pointer. I am at a loss for what could be causing it. Any suggestions? import java.io.*; import java.util.*; public class Reading_Lvl_Calc { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int words = 0; String fileName; Scanner scan; Scanner keyread = new Scanner(System.in); System.out.println("Please enter a file name (or QUIT to exit)"); fileName = keyread.nextLine(); File doc = new File(fileName); //while(scan.equals(null)){ try { scan = new Scanner(doc); } catch(Exception e) { if(fileName.substring(fileName.indexOf(".")) != ".txt") System.out.println("I'm sorry, the file \"" + fileName + "\" has an invalid file extension."); else System.out.println("I am sorry, the file \"" + fileName + " \" cannot be found.\n The file must be in the same directory as this program"); scan = null; } // } while(scan.hasNext()){ words++; scan.next(); } System.out.println(words); } }

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  • How to solve this Java type safety warning? (Struts2)

    - by Nicolas Raoul
    Map session = ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map should be parameterized. Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: Unchecked cast from Map to Map. The getSession method belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful. I guess all Struts2 users in the world faced the same problem... is there an elegant solution?

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