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  • Can I avoid repeating myself in this situation (Java)

    - by UltimateGuy
    if (openFile == null) { new AppFileDialog().chooseFile("Save", appFrame); } if (openFile == null) { return; } Here I need to check to see if the user has already chosen a file. If not, they are given a prompt to. If the file is still null, the function returns without saving. The problem is the two identical if statements, can I avoid it? I take DRY very seriously, but at the same time KISS. Ideally the two go hand in hand, but in a situation like this, it seems they are mutually exclusive.

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  • Avoiding duplicate objects in Java deserialization

    - by YGL
    I have two lists (list1 and list2) containing references to some objects, where some of the list entries may point to the same object. Then, for various reasons, I am serializing these lists to two separate files. Finally, when I deserialize the lists, I would like to ensure that I am not re-creating more objects than needed. In other words, it should still be possible for some entry of List1 to point to the same object as some entry in List2. MyObject obj = new MyObject(); List<MyObject> list1 = new ArrayList<MyObject>(); List<MyObject> list2 = new ArrayList<MyObject>(); list1.add(obj); list2.add(obj); // serialize to file1.ser ObjectOutputStream oos = new ObjectOutputStream(...); oos.writeObject(list1); oos.close(); // serialize to file2.ser oos = new ObjectOutputStream(...); oos.writeObject(list2); oos.close(); I think that sections 3.4 and A.2 of the spec say that deserialization strictly results in the creation of new objects, but I'm not sure. If so, some possible solutions might involve: Implementing equals() and hashCode() and checking references manually. Creating a "container class" to hold everything and then serializing the container class. Is there an easy way to ensure that objects are not duplicated upon deserialization? Thanks.

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  • Generate a collection of changed lines between two revisions of a file using Java

    - by mchr
    I am writing an eclipse plugin which needs to be able to determine which lines of a file have changed compared to a different version of the same file. Is there an existing class or library which I can use for this task? The closest I have found is org.eclipse.compare.internal.merge.DocumentMerger. This can be used to find the information I need but is in an internal package so is not suitable for me to use. I could copy/paste the source of this class and adapt it to my requirements. However, I am hoping there is an existing library to handle textual comparisons.

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  • Statically checking a Java app for link errors

    - by monorailkitty
    I have a scenario where I have code written against version 1 of a library but I want to ship version 2 of the library instead. The code has shipped and is therefore not changeable. I'm concerned that it might try to access classes or members of the library that existed in v1 but have been removed in v2. I figured it would be possible to write a tool to do a simple check to see if the code will link against the newer version of the library. I appreciate that the code may still be very broken even if the code links. I am thinking about this from the other side - if the code won't link then I can be sure there is a problem. As far as I can see, I need to run through the bytecode checking for references, method calls and field accesses to library classes then use reflection to check whether the class/member exists. I have three-fold question: (1) Does such a tool exist already? (2) I have a niggling feeling it is much more complicated that I imagine and that I have missed something major - is that the case? (3) Do you know of a handy library that would allow me to inspect the bytecode such that I can find the method calls, references etc.? Thanks!

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  • iBatis not populating object when there are no rows found.

    - by Omnipresent
    I am running a stored procedure that returns 2 cursors and none of them have any data. I have the following mapping xml: <resultMap id="resultMap1" class="HashMap"> <result property="firstName" columnIndex="2"/> </resultMap> <resultMap id="resultMap2" class="com.somePackage.MyBean"> <result property="unitStreetName" column="street_name"/> </resultMap> <parameterMap id="parmmap" class="map"> <parameter property="id" jdbcType="String" javaType="java.lang.String" mode="IN"/> <parameter property="Result0" jdbcType="ORACLECURSOR" javaType="java.sql.ResultSet" mode="OUT" resultMap="resultMap1"/> <parameter property="Result1" jdbcType="ORACLECURSOR" javaType="java.sql.ResultSet" mode="OUT" resultMap="resultMap2"/> </parameterMap> <procedure id="proc" parameterMap="parmmap"> { call my_sp (?,?,?) } </procedure> First result set is being put in a HashMap...second resultSet is being put in a MyBean class. code in my DAO follows: HashMap map = new HashMap() map.put("id", "1234"); getSqlMapClientTemplate().queryForList("mymap.proc", map); HashMap result1 = (HashMap)((List)parmMap.get("Result0")).get(0); MyBean myObject = (MyBean)((List)parmMap.get("Result1")).get(0);//code fails here in the last line above..my code fails. It fails because second cursor has no rows and thats why nothing is put into the list. However, first cursor returns nothing as well but since results are being put into a HashMap the list for first cursor atleast has HashMap object inside it.. Why this difference? is there a way to make iBatis put an object of MyBean inside the list even if there are no rows returned? Or should I be handling this in my DAO...I want to avoid handling it in the DAO because I have whole bunch of DAO's like these.

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  • java detect clicked buttons

    - by user253530
    I have multiple panels on a JFrame window. I am going to populate each panel differently every time. For example: i start the GUI: (image center panel, right panel, bottom panel). Center panel is populated with 20 buttons, right panel with 10 buttons and bottom panel with 3. second start of the GUI (same gui). Center panel has 50 buttons, right panel has 12 buttons, bottom has 3. So everytime there is a random number of buttons, impossible to be all uniquely named. Given the fact that I don't have a unique name for each button (just a list) I would like to know which buttons were clicked according to the panel they belong to. is that possible?

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  • synchronized in java - Proper use

    - by ZoharYosef
    I'm building a simple program to use in multi processes (Threads). My question is more to understand - when I have to use a reserved word synchronized? Do I need to use this word in any method that affects the bone variables? I know I can put it on any method that is not static, but I want to understand more. thank you! here is the code: public class Container { // *** data members *** public static final int INIT_SIZE=10; // the first (init) size of the set. public static final int RESCALE=10; // the re-scale factor of this set. private int _sp=0; public Object[] _data; /************ Constructors ************/ public Container(){ _sp=0; _data = new Object[INIT_SIZE]; } public Container(Container other) { // copy constructor this(); for(int i=0;i<other.size();i++) this.add(other.at(i)); } /** return true is this collection is empty, else return false. */ public synchronized boolean isEmpty() {return _sp==0;} /** add an Object to this set */ public synchronized void add (Object p){ if (_sp==_data.length) rescale(RESCALE); _data[_sp] = p; // shellow copy semantic. _sp++; } /** returns the actual amount of Objects contained in this collection */ public synchronized int size() {return _sp;} /** returns true if this container contains an element which is equals to ob */ public synchronized boolean isMember(Object ob) { return get(ob)!=-1; } /** return the index of the first object which equals ob, if none returns -1 */ public synchronized int get(Object ob) { int ans=-1; for(int i=0;i<size();i=i+1) if(at(i).equals(ob)) return i; return ans; } /** returns the element located at the ind place in this container (null if out of range) */ public synchronized Object at(int p){ if (p>=0 && p<size()) return _data[p]; else return null; }

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  • Need a hand understanding this Java code please :-)

    - by Brian
    Hi all, Just wondering if anyone would be able to take a look at this code for implementing the quicksort algorithm and answer me a few questions, please :-) public class Run { /*************************************************************************** * Quicksort code from Sedgewick 7.1, 7.2. **************************************************************************/ public static void quicksort(double[] a) { //shuffle(a); // to guard against worst-case quicksort(a, 0, a.length - 1, 0); } static void quicksort(final double[] a, final int left, final int right, final int tdepth) { if (right <= left) return; final int i = partition(a, left, right); if ((tdepth < 4) && ((i - left) > 1000)) { final Thread t = new Thread() { public void run() { quicksort(a, left, i - 1, tdepth + 1); } }; t.start(); quicksort(a, i + 1, right, tdepth + 1); try { t.join(); } catch (InterruptedException e) { throw new RuntimeException("Cancelled", e); } } else { quicksort(a, left, i - 1, tdepth); quicksort(a, i + 1, right, tdepth); } } // partition a[left] to a[right], assumes left < right private static int partition(double[] a, int left, int right) { int i = left - 1; int j = right; while (true) { while (less(a[++i], a[right])) // find item on left to swap ; // a[right] acts as sentinel while (less(a[right], a[--j])) // find item on right to swap if (j == left) break; // don't go out-of-bounds if (i >= j) break; // check if pointers cross exch(a, i, j); // swap two elements into place } exch(a, i, right); // swap with partition element return i; } // is x < y ? private static boolean less(double x, double y) { return (x < y); } // exchange a[i] and a[j] private static void exch(double[] a, int i, int j) { double swap = a[i]; a[i] = a[j]; a[j] = swap; } // shuffle the array a[] private static void shuffle(double[] a) { int N = a.length; for (int i = 0; i < N; i++) { int r = i + (int) (Math.random() * (N - i)); // between i and N-1 exch(a, i, r); } } // test client public static void main(String[] args) { int N = 5000000; // Integer.parseInt(args[0]); // generate N random real numbers between 0 and 1 long start = System.currentTimeMillis(); double[] a = new double[N]; for (int i = 0; i < N; i++) a[i] = Math.random(); long stop = System.currentTimeMillis(); double elapsed = (stop - start) / 1000.0; System.out.println("Generating input: " + elapsed + " seconds"); // sort them start = System.currentTimeMillis(); quicksort(a); stop = System.currentTimeMillis(); elapsed = (stop - start) / 1000.0; System.out.println("Quicksort: " + elapsed + " seconds"); } } My questions are: What is the purpose of the variable tdepth? Is this considered a "proper" implementation of a parallel quicksort? I ask becuase it doesn't use implements Runnable or extends Thread... If it doesn't already, is it possible to modify this code to use multiple threads? By passing in the number of threads you want to use as a parameter, for example...? Many thanks, Brian

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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: Difference between PrintStream and PrintWriter

    - by Martijn Courteaux
    Hi, What is the difference between PrintStream and PrintWriter? They have much methods in common. I always mix up this classes because of that reason. And I think we can use them for exactly the same. But there has to be a difference. Otherwise there was only one class. I first searched on StackOverflow, but not yet this question. Thanks

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  • Internal Java code best practice for dealing with invalid REST API parameters

    - by user326389
    My colleague wrote the following stackoverflow question: other stack overflow question on this topic The question seems to have been misinterpreted and I want to find out the answer, so I'm starting this new question... hopefully a little more clear. Basically, we have a REST API. Users of our API call our methods with parameters. But sometimes users call them with the wrong parameters!! Maybe a mistake in their code, maybe they're just trying to play with us, maybe they're trying to see how we respond, who knows! We respond with HTTP status error codes and maybe a detailed description of the invalid parameter in the XML response. All is well. But internally we deal with these invalid parameters by throwing exceptions. For example, if someone looks up a Person object by giving us their profile id, but the profile id doesn't exist... we throw a PersonInvalidException when looking them up. Then we catch this exception in our API controller and send back an HTTP 400 status error code. Our question is... is this the best practice, throwing exceptions internally for this kind of user error? These exceptions never get propogated back to the user, this is a REST API. They only make our code cleaner. Otherwise we could have a validation method in each of our API controllers to make sure the parameters all make sense, but that seems inefficient. We have to look up things in our database potentially twice. Or we could return nulls and check for them, but that sucks... What are your thoughts?

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  • Java: Convenient way to refactor the application.

    - by Harshal
    Hi, Everyone We have an agile enterprise application built on JSP and Servlet without any design strategy. This application was built in early 2002 considering 1000 users. After 2002, we received lots of requests from the marketing partners. Currently, the application has lots of spaghetti code with lots of Ifs and elses. One class has more than 20,000 lines of code with a huge body of functions without abstraction. Now, we need to support billions of records, what we need to do immediately and gradually? We have to refactor the application? Which framework, we need to use? How the usage of the framework will be helpful to the end users? How to convince the leaders to do the refactoring? How to gain the faster response time as compare to the current system?

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  • Java URI.resolve

    - by twip
    I'm trying to resolve two URIs, but it's not as straightforward as I'd like it to be. URI a = new URI("http://www.foo.com"); URI b = new URI("bar.html"); The trouble is that a.resolve(b).toString() is now "http://www.foo.combar.html". How can I get away with that?

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  • Android / Java rare and seemingly impossible exception causing force close

    - by Guzba
    Hello all, I have an interesting problem being reported to me from an android application I have published. I have a two-dimensional array that I am iterating through using two for loops like so: for (int i = 0; i < arr.length; ++i) { for (int j = 0; j < arr[i].length; ++j) { if (arr[i][j] != 0) // does stuff } } The problem is, somehow arr[i][j] != 0 is throwing an ArrayIndexOutOfBoundsException. But very rarely. I have thousands of people use the app on a daily basis and get maybe twenty force close reports. Is this something I can't avoid, maybe a problem with the phones memory, etc. or is there something I can do that I haven't thought of yet? Thanks.

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  • Changing Encoding while Xml.parse() with SaxFeedParser Java

    - by zOro
    Hi , I am trying to load hebrew rss using the fllow : Xml.parse(_InputStream, Xml.Encoding.ISO_8859_1 , root.getContentHandler()); taken from ibm site : link text I would like to use other Encoding like "ISO8859_8" rather than : Xml.Encoding.ISO_8859_1, Xml.Encoding.US_ASCII, Xml.Encoding.UTF_16, Xml.Encoding.UTF_8 Thanks a lot!

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  • Java Hibernate Lazy=false

    - by Noor
    When setting Lazy=false, then hibernate will automatically loads the objects into the required sets e.g. <set name="Options" table="ATTRIBUTEOPTION" inverse="false" cascade="all" lazy="false"> <key> <column name="ATTRIBUTEID" /> </key> <one-to-many class="com.BiddingSystem.Models.AttributeOption" /> </set> but if in my xml mapping, I place lazy=true and in some place in my application i decide that i want to load all attribute options, should i do it manually, or is there a technique which lets tells hibernate that now i want to set lazy=false??

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  • Java URL Connection Time Out

    - by webren
    Hello, I am attempting to connect to a website where I'd like to extract its HTML contents. My application will never connect to the site - only time out. Here is my code: URL url = new URL("www.website.com"); URLConnection connection = url.openConnection(); connection.setConnectTimeout(2000); connection.setReadTimeOut(2000); BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()); String line; while ((line = reader.readLine()) != null) { // do stuff with line } reader.close(); Any ideas would be greatly appreciated. Thanks!

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  • JAVA-I don't want clicking on my app make other apps lose focus

    - by Auxiliary
    Wow, what a stupid question you might say. But is it possible? I have a mouse move event in a Jpanel and it works even when the application is not in focus, now can I have something like that for the clicking event or something similar. And most importantly I don't want other apps (even something like the main menu) to lose focus when i click on my app. I was the system's event queue but i'm not sure where that would lead me to. Thanks in advance.

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  • How to find the largest square in the number (Java)

    - by Ypsilon IV
    Hello everyone, I want to find the largest square in the number, but I am stuck at some point. I would really appreciate some suggestions. This is what I've done so far: I take the number on the input, factorize into prime numbers, and put the sequence of prime numbers to ArrayList. Numbers are sorted, in a sense, thus the numbers in the sequence are increasing. For example, 996 is 2 2 3 83 1000 is 2 2 2 5 5 5 100000 is 2 2 2 2 2 5 5 5 5 5 My idea now is to count number of occurrences of each elements in the sequence, so if the number of occurrences is divisible by two, then this is the square. In this way, I can get another sequence, where the right most element divisible by two is the largest square. What is the most efficient way to count occurrences in the ArrayList? Or is there any better way to find the largest square? Many thanks in advance!

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  • Please clarify a few points concerning Java Servlets

    - by EugeneP
    suppose, I use Tomcat as a web container. Is it true that once all the servlets found in a web-app/WEBAPPNAME are init(IALIZED) then every change of a Servlet's property will be seen to every session. So session 1 changes a property userName of a Servlet1 from "user1" to "user2" session 1 is closed. session 2 starts. It will see "user2" as the only value of Servlet1.userName property?? Any change of a Servlet's field will be seen to all subsequent sessions? Are servlets singletons, aren't they?

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  • java programming

    - by Baiba
    ok i have version of t code, please tell me what i need to do when i need to get out of program The INDEX NUMBER OF COLUMN IN WHICH ARE LEAST ZEROS? class Uzd{ public static void main(String args[]){ int mas[][]= {{3,4,7,5,0}, {4,5,3,0,1}, {8,2,4,0,3}, {7,0,2,0,1}, {0,0,1,3,0}}; int nul_mas[] = new int[5]; int nul=0; for(int j=0;j<5;j++){// nul=0; for(int i=0;i<5;i++){ if(mas[i][j]==0){ nul++; } } nul_mas[j]=nul; } for(int i=0;i<5;i++){ for(int j=0;j<5;j++){ System.out.print(mas[i][j]); } System.out.println(); } System.out.println();// atstarpe System.out.println("///zeros in each column///"); for(int i=0;i<5;i++){System.out.print(nul_mas[i]);} System.out.println(); }} and after running it shows: 34750 45301 82403 70201 00130 ///zeros in each column/// But i need not in each column but i need to get out index of column in which zeros are least! in this situation it is column nubmer 2!! 12032

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  • Java Swing - Adding a row # column (row header) to a JTable

    - by llm
    I have data from a database loaded into a JTable through a custom table model. I want to have a column (should be the first column) which simply shows the display row number (i.e. it is not tied to any data (or sorting) but is simply the row number on the screen starting at 1). These "row headers" should be grayed out like the row headers. Any idea how to do this? Thanks

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