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  • Gracefully avoiding NullPointerException in Java

    - by Yuval A
    Consider this line: if (object.getAttribute("someAttr").equals("true")) { // .... Obviously this line is a potential bug, the attribute might be null and we will get a NullPointerException. So we need to refactor it to one of two choices: First option: if ("true".equals(object.getAttribute("someAttr"))) { // .... Second option: String attr = object.getAttribute("someAttr"); if (attr != null) { if (attr.equals("true")) { // .... The first option is awkward to read but more concise, while the second one is clear in intent, but verbose. Which option do you prefer in terms of readability?

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • Revalidate and repaint - Java Swing

    - by bosra
    I have a JPanel that I am adding JLabel's to. I then want to remove all the JLabels and add some new ones. So I do the following: panel.removeAll();panel.repaint(); panel.add(new JLabel("Add something new"); panel.revalidate(); This works fine. My problem arises when I start a new thread after this like: panel.removeAll();panel.repaint(); (1)panel.add(new JLabel("Add something new"); panel.revalidate(); //new thread to start - this thread creates new JLabels that should appear under (1) firstProducer.start(); try { firstProducer.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Then the output from the original JLabels is still visible. I have read that the revalidate process is a long running task and hence the firstProducer thread is getting started while the revalidation is going on and a conflict is arising. What is the best way to deal with this?

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  • java regular expression

    - by BSingh
    I am trying to write a regular expression for somethin like s1 = I am at Boston at Dowtown s2 = I am at Miami I am interested in the words after at eg: Boston, Downtown, Miami I have not been successful in creating a regex for that. Somethin like > .*? (at \w+)+.* gives just Boston in s1 (Downtown is missed). it just matches the first "at" Any suggestions

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  • Java data structure suggestion.

    - by techoverflow
    Hi folks, I am a newbie in this field so please excuse my silly mistakes :) So the issue I am facing is: On my webpage, I am displaying a table. For now my issue is concerned with three columns of the table. First is : Area Code Second is : Zone Code Third is: Value The relationship between these three is: 1 Area Code has 6 different Zone code's and all those 6 Zone codes have corresponding "Value" I need a data structer that would give me the flexibility to get a "Value" for a Zone code, which falls under a particular Area code. I have the same zone codes for all the Area codes: Zone codes are: 111, 222, 333, 444, 555, 666 After surfing your stackoverflow, I thought I can go with this structure: Map<Integer, Map<Integer, Double>> retailPrices = new HashMap<Integer, Map<Integer, Double>>(); Map<Integer, Double> codes = new HashMap<Integer, Double>(); where reatailPrices would hold an Area Code and a Map of Zone code as Key and "Value" as Value. but when I am trying to populate this through a SQL resultset, I am getting the following error: The method put(Integer, Map<Integer,Double>) in the type Map is not applicable for the arguments (Integer, Double) on line: `while(oResult.next()) retailPrices.put((new Integer(oResult.getString("AREA"))), (pegPlPrices.put(new Integer(oResult.getString("ZONE_CODE")), new Double(oResult.getString("VALUE"))))); }` please help me figure out this problem. Am I following the right approach?

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  • Authorization engine in java

    - by eltados
    In the course of my work i need to develop an authorization engine ( i'm already authenticated and i check access of a user to an action ) in order to store all the authorization logic inside a same place and be able to reuse it and i have created the mini library. http://github.com/eltados/canny what do you think about it? Is there any lightweight Authorization engine library i could have a look at?

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  • How to explicitly add a piece of code to a java project

    - by user435245
    Hi there, I’m working with Net beans IDE and I want to add a piece of code to my project in a way that the source code won’t be visible to the user who is running the project, I decided to export that piece of code as a jar file in eclipse and then add that jar file to the project. But unfortunately net beans does not let me import that. It says which it is expecting a . Or when I insert. It goes in to that class and I cannot import that jar file into the project by import instruction. Is there a command in net beans which creates and object from jar file and then makes access to the functions and classes of the jar file? Would you please give the format of that instruction? If you know a better way to do this task I would be so happy if you share it with me

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  • Profiling a Java Spring application

    - by niklassaers
    Hi guys, I have a Spring application that I believe has some bottlenecks, so I'd like to run it with a profiler to measure what functions take how much time. Any recommendations to how I should do that? I'm running STS, the project is a maven project, and I'm running Spring 3.0.1 Cheers Nik

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  • Count the number of dates between two dates

    - by Matt Mitchell
    I'm looking to count the dates covered (inclusive) between two DateTimes (not .TotalDays) For example: 2012-2-1 14:00 to 2012-2-2 23:00 -> 2 2012-2-1 14:00 to 2012-2-2 10:00 -> 2 2012-2-1 14:00 to 2012-2-1 15:00 -> 1 2012-1-1 00:00 to 2012-12-31 23:59 -> 366 I can get this functionality with the code below: DateTime dt1 = new DateTime(2000,1,2,12,00,00); DateTime dt2 = new DateTime(2000,1,3,03,00,00); int count = 0; for (DateTime date = dt1; date.Date <= dt2.Date; date = date.AddDays(1)) count++; return count; Is there a better way?

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  • Java serialization testing

    - by Jeff Storey
    Does anyone know if there is a library that exists to help test if an object graph is fully serializable? It would probably be as simple as writing it out and reading it back in, but I figured someone must have abstracted this already - I just can't find it.

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  • Java Web App: Passing form parameters across multiple pages

    - by digiarnie
    Hi, what is the best practice or best way of passing form parameters from page to page in a flow? If I have a flow where a user enters data in a form and hits next and repeats this process until they get to an approval page, what ways could I approach this problem to make the retention of data as simple as possible over the flow? I guess you could put all the information as you go in the session but could you get into memory issues if a lot of people are using your app and going through the flow at the same time?

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  • Java/Swing: Problem with key listener

    - by Mike
    I have a search dialog with a JTextField that's being used as a search box. When the user types something, it searches the DB, shows the result in a JTable and selects the first item in it. If the first result is what they were looking for, I want to let them quickly accept the dialog, by pressing Enter (while the JTextField is focused). So I added a KeyListener to the JTextField and it's working OK. Now the problem: The user opens can open the dialog by pressing Enter when a "Search" button on the dialog's parent frame is focused. The dialog is displayed and the JTextField gets the keyReleased event (from the Enter key that displayed it), so it shows up and closes. If the user holds Enter down, then the JTextField receives the keyPressed, keyTyped and keyReleased events. How can I fix without resorting to ugly workarounds? Platform is Windows 7 x64, btw. Test NetBeans project here: http://dl.dropbox.com/u/6354360/KeyListenerTest.zip Thanks.

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  • Java: JPQL search -similar- strings

    - by bguiz
    What methods are there to get JPQL to match similar strings? By similar I mean: Contains: search string is found within the string of the matches entity Case-insensitive Small mispellings: e.g. "arow" matches "arrow" I suspect the first two will be easy, however, I would appreciate help with the last one Thank you

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  • Java method: retrieve the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). *Sorry but I can't type closing braces

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  • Embeddable database better than SQLite for java

    - by dexter
    I am creating a web application that is accessing a SQLite database in the server. I also have "clients" that updates this same database. As we know SQLite locks the entire database during INSERTs which are done by the clients and the web application is also trying to make some UPDATEs at the same time. So my problem now is about concurrency in database access. I would like to use an embeddable database like SQLite. Any suggestions.

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  • How to check if EditText has a value in Android / Java

    - by Allen Gingrich
    This should be simple, but I have tried if statements checking for null values and also ones checking the .length of it: EditText marketValLow = (EditText) findViewById(R.id.marketValLow); EditText marketValHigh = (EditText) findViewById(R.id.marketValHigh); if (marketValLow.getText().length() != 0 && marketValHigh.getText().length() != 0) { Intent intent = new Intent(); intent.setClass(v.getContext(), CurrentlyOwe.class); startActivity(intent); } else { Toast.makeText(CurrentMarketValue.this, "You need to enter a high AND low.", Toast.LENGTH_SHORT); } But it doesn't detect nothing was entered. Any ideas? Thanks!

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  • How to pass checkbox array to Java from jsp

    - by eddy
    Hi, I'd like to know if there's any way to send data to the server for the selected rows using the checkboxes I've put on those rows? I mean , how can I send only the data of those selected rows to the server? Here's the html code I use: <table> <thead> <tr class="tableheader"> <td width="10%"></td> <td width="30%">Vehicle</td> <td width="40%">Driver</td> <td width="10%">Mileage</td> </tr> </thead> <tbody> <c:forEach items="${list}" var="item"> <tr> <td align="center"> <input type="checkbox" name="selectedItems" value="c:out value="${item.numberPlate}"/>"/> </td> <td align="left"><c:out value="${item.numberPlate}"/></td> <td align="left"><c:out value="${item.driver.fullName}" /></td> <td align="left"><input type="text" name="mileage" value="" /></td> </tr> </c:forEach> </tbody> </table> I really hope you can give some guidance on this. Thanks in beforehand.

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  • Java Generic Type and Reflection

    - by Tom Tucker
    I have some tricky generic type problem involving reflection. Here's the code. public @interface MyConstraint { Class<? extends MyConstraintValidator<?>> validatedBy(); } public interface MyConstraintValidator<T extends Annotation> { void initialize(T annotation); } /** @param annotation is annotated with MyConstraint. */ public void run(Annotation annotation) { Class<? extends MyConstraintValidator<? extends Annotation>> validatorClass = annotation.annotationType().getAnnotation(MyConstraint.class).validatedBy(); validatorClass.newInstance().initialize(annotation) // will not compile! } The run() method above will not compile because of the following error. The method initialize(capture#10-of ? extends Annotation) in the type MyConstraintValidator<capture#10-of ? extends Annotation> is not applicable for the arguments (Annotation) If I remove the wild cards, then it compiles and works fine. What would be the propert way to declare the type parameter for the vairable validatorClass? Thanks.

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  • Java static method parameters

    - by Blitzkr1eg
    Why does the following code return 100 100 1 1 1 and not 100 1 1 1 1 ? public class Hotel { private int roomNr; public Hotel(int roomNr) { this.roomNr = roomNr; } public int getRoomNr() { return this.roomNr; } static Hotel doStuff(Hotel hotel) { hotel = new Hotel(1); return hotel; } public static void main(String args[]) { Hotel h1 = new Hotel(100); System.out.print(h1.getRoomNr() + " "); Hotel h2 = doStuff(h1); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); h1 = doStuff(h2); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); } } Why does it appear to pass Hotel by-value to doStuff() ?

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  • Parse XML with XPath & namespaces in Java

    - by ripper234
    Can you help me adjust this code so it manages to parse the XML? If I drop the XML namespace it works: String webXmlContent = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" + "<foo xmlns=\"http://foo.bar/boo\"><bar>baz</bar></foo>"; DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance(); domFactory.setNamespaceAware(true); DocumentBuilder builder = domFactory.newDocumentBuilder(); org.w3c.dom.Document doc = builder.parse(new StringInputStream(webXmlContent)); NamespaceContextImpl namespaceContext = new NamespaceContextImpl(); namespaceContext.startPrefixMapping("foo", "http://www.w3.org/2001/XMLSchema-instance"); XPath xpath = XPathFactory.newInstance().newXPath(); xpath.setNamespaceContext(namespaceContext); XPathExpression expr = xpath.compile("/foo/bar"); Object result = expr.evaluate(doc, XPathConstants.NODESET); NodeList nodes = (NodeList) result; System.out.println("Got " + nodes.getLength() + " nodes");

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  • Java: how to use Google's HashBiMap?

    - by HH
    Keys are a file and a word. The file gives all words inside the file. The word gives all files having the word. I am unsure of the domain and co-domain parts. I want K to be of the type <String> and V to be of type <HashSet<FileObject>>. public HashBiMap<K<String>,V<HashSet<FileObject>>> wordToFiles = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); public HashBiMap<K<String>,V<HashSet<FileObject>>> fileToWords = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); Google's HashBiMap.

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  • Better way to write this Java code?

    - by Macha
    public void handleParsedCommand(String[] commandArr) { if(commandArr[0].equalsIgnoreCase("message")) { int target = Integer.parseInt(commandArr[1]); String message = commandArr[2]; MachatServer.sendMessage(target, this.conId, message); } else if(commandArr[0].equalsIgnoreCase("quit")) { // Tell the server to disconnect us. MachatServer.disconnect(conId); } else if(commandArr[0].equalsIgnoreCase("confirmconnect")) { // Blah blah and so on for another 10 types of command } else { try { out.write("Unknown: " + commandArr[0] + "\n"); } catch (IOException e) { System.out.println("Failed output warning of unknown command."); } } } I have this part of my server code for handling the types of messages. Each message contains the type in commandArr[0] and the parameters in the rest of commandArr[]. However, this current code, while working seems very unelegant. Is there a better way to handle it? (To the best of my knowledge, String values can't be used in switch statements, and even then, a switch statement would only be a small improvement.

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  • Java Timer not working

    - by Jacob
    I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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