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  • String intern puzzles

    - by Yob
    On this blog I found interesting String puzzles: --- Quote --- String te = "te", st = "st"; //"test".length(); String username = te + st; username.intern(); System.out.println("String object the same is: " + (username == "test")); prints String object the same is: true but uncomment the "test".length(); line and it prints String object the same is: false --- EoQ --- Being honest I don't understand why the outputs are different. Could you please explain me what's the cause of such behaviour?

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  • Do you put a super() call a the beginning of your constructors?

    - by sleske
    This is a question about coding style and recommended practices: As explained in the answers to the question unnecessary to put super() in constructor?, if you write a constructor for a class that is supposed to use the default (no-arg) constructor from the superclass, you may call super() at the beginning of your constructor: public MyClass(int parm){ super(); // leaving this out makes no difference // do stuff... } but you can also omit the call; the compiler will in both cases act as if the super() call were there. So then, do you put the call into your constructors or not? On the one hand, one might argue that including the super() makes things more explicit. OTOH, I always dislike writing redundant code, so personally I tend to leave it out; I do however regularly see it in code from others. What are your experiences? Did you have problems with one or the other approach? Do you have coding guidelines which prescribe one approach?

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  • Two entities with @ManyToOne should join the same table

    - by Ivan Yatskevich
    I have the following entities Student @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Teacher @Entity public class Teacher implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; //getter and setter for id } Task @Entity public class Task implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "student_id") }) private Student author; @ManyToOne(optional = false) @JoinTable(name = "student_task", inverseJoinColumns = { @JoinColumn(name = "teacher_id") }) private Teacher curator; //getters and setters } Consider that author and curator are already stored in DB and both are in the attached state. I'm trying to persist my Task: Task task = new Task(); task.setAuthor(author); task.setCurator(curator); entityManager.persist(task); Hibernate executes the following SQL: insert into student_task (teacher_id, id) values (?, ?) which, of course, leads to null value in column "student_id" violates not-null constraint Can anyone explain this issue and possible ways to resolve it?

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  • getSystemResourceAsStream() returns null

    - by Hitesh Solanki
    Hiii... I want to get the content of properties file into InputStream class object using getSystemResourceAsStream(). I have built the sample code. It works well using main() method,but when i deploy the project and run on the server, properties file path cannot obtained ... so inputstream object store null value. Sample code is here.. public class ReadPropertyFromFile { public static Logger logger = Logger.getLogger(ReadPropertyFromFile.class); public static String readProperty(String fileName, String propertyName) { String value = null; try { //fileName = "api.properties"; //propertyName = "api_loginid"; System.out.println("11111111...In the read proprty file....."); // ClassLoader loader = ClassLoader.getSystemClassLoader(); InputStream inStream = ClassLoader.getSystemResourceAsStream(fileName); System.out.println("In the read proprty file....."); System.out.println("File Name :" + fileName); System.out.println("instream = "+inStream); Properties prop = new Properties(); try { prop.load(inStream); value = prop.getProperty(propertyName); } catch (Exception e) { logger.warn("Error occured while reading property " + propertyName + " = ", e); return null; } } catch (Exception e) { System.out.println("Exception = " + e); } return value; } public static void main(String args[]) { System.out.println("prop value = " + ReadPropertyFromFile.readProperty("api.properties", "api_loginid")); } }

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  • Is dependency injection only for service type objects and singletons? (and NOT for gui?)

    - by sensui
    I'm currently experimenting with the Google's guice inversion of control container. I previously had singletons for just about any service (database, active directory) my application used. Now I refactored the code: all the dependencies are given as parameters to constructors. So far, so good. Now the hardest part is with the graphical user interface. I face this problem: I have a table (JTable) of products wrapped in an ProductFrame. I give the dependencies as parameters (EditProductDialog). @Inject public ProductFrame(EditProductDialog editProductDialog) { // ... } // ... @Inject public EditProductDialog(DBProductController productController, Product product) { // ... } The problem is that guice can't know what Product I have selected in the table, so it can't know what to inject in the EditProductDialog. Dependency Injection is pretty viral (if I modify one class to use dependency injection I also need to modify all the other classes it interacts with) so my question is should I directly instantiate EditProductDialog? But then I would have to pass manually the DBProductController to the EditProductDialog and I will also need to pass it to the ProductFrame and all this boils down to not using dependency injection at all. Or is my design flawed and because of that I can't really adapt the project to dependecy injection? Give me some examples of how you used dependency injection with the graphical user interface. All the examples found on the Internet are really simple examples where you use some services (mostly databases) with dependency injection.

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  • DYNAMICALLY CHANGE JCOMBOBOX

    - by Suman.hassan95
    i am fetching the data values from the database success fully. I have also stored them into a String array. I need to load the String array as the items of the ComboBox in response to key actionperformed . How can i reload the items of the ComboBox whenever a key is pressed as the fetched values depend on the key pressed. Rather simply, i need to dynamically refresh the ComboBox items. please help.

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  • Advantages of using a Dynamic Client with JAX-WS

    - by jconlin
    What are the advantages of using a dynamic client with JAX-WS services as opposed to just using generated client classes? What are the disadvantages? **For my particular case I am using Apache CXF, I'm not sure what other libraries allow "dynamic" clients. -I thought I didn't need to add this, but... I'm looking for non-obvious(I know...subjective) advantages. I don't need someone else to tell me that an advantage of not using generated classes is that I don't need to generate classes.

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  • Value isnt being saved in the strings

    - by Raptrex
    I'm trying to make a class where I put a key and value into the put method which puts the key in the k string array and value into the v string array, however it is not being saved in the array when I do get or display. For example: put(dan,30) get(dan) returns null display returns null null 10 times. Anyone know whats wrong? public class Memory { final int INITIAL_CAPACITY = 10; String[] k = new String[INITIAL_CAPACITY]; String[] v = new String[INITIAL_CAPACITY]; int count = 0; public Memory() { count = 0; } public int size() { return count; } public void put(String key, String value) { int a = 0; boolean found = false; for (int i = 0; i < k.length; i++) { //System.out.println("key is " + key.equals(k[i])); if (key.equalsIgnoreCase(k[i])) { v[i] = value; found = true; } if (found) break; a++; } //System.out.println(a == k.length); if (a == k.length); { k[count] = key; v[count] = value; //System.out.println(k[count] + " " + v[count]); count++; //System.out.println(count); } } public String get(String key) { String output = "a"; for(int i = 0; i < k.length; i++) { if(!key.equalsIgnoreCase(k[i])) { output = null; } else { output = v[i]; return output; } } return output; } public void clear() { for (int i = 0; i < k.length; i++) { k[i] = null; v[i] = null; } count = 0; } public void display() { for (int i = 0; i < k.length; i++) { System.out.println(k[i] + " " + v[i]); } } }

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  • how to remove ConcurrentModificationException

    - by maverick
    what is this exception and how to remove this in my problem i am creating an arraylist of objects, and after checking some condition,i want to remove some objects. but the program is giving this exception ConcurrentModificationException. how to remove this thanks in advance

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  • Why are static imports of static methods with same names legal?

    - by user1055638
    Lets say we have these packages and classes: package p1; public class A1 { public static void a() {} } package p2; public class A1 { public static void a() {} } package p3; import static p1.A1.a; import static p2.A1.a; public class A1 { public static void test() { } } I am wondering, why the static import of methods is legal (won't result in compile time error) in package p3? We won't be able to use them further in the test() method as such usage will result in the compile time error. Why it is not the same as with a normal import of classes. Lets say we would like to import classes A1 from packages p1 and p2 into p3: package p3; import p1.A1; import p2.A1; such import is illegal and will result in the compile time error.

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  • Using JSF, JPA and DAO. Without Spring?

    - by ich-bin-drin
    Hi, till now i still worked with JSF and JPA without DAOs. Now i'd like to use DAOs. But how can i initialize the EntityManager in the DAO-Classes? public class AdresseHome { @PersistenceContext private EntityManager entityManager; public void persist(Adresse transientInstance) { log.debug("persisting Adresse instance"); try { entityManager.persist(transientInstance); log.debug("persist successful"); } catch (RuntimeException re) { log.error("persist failed", re); throw re; } } } Have I to use Spring or is there a solution that works without Spring? Thanks.

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  • Swt file dialog too much files selected?

    - by InsertNickHere
    Hi there, the swt file dialog will give me an empty result array if I select too much files (approx. 2500files). The listing shows you how I use this dialog. If i select too many sound files, the syso will show 0. Debugging tells me, that the files array is empty in this case. Is there any way to get this work? FileDialog fileDialog = new FileDialog(mainView.getShell(), SWT.MULTI); fileDialog.setText("Choose sound files"); fileDialog.setFilterExtensions(new String[] { new String("*.wav") }); Vector<String> result = new Vector<String>(); fileDialog.open(); String[] files = fileDialog.getFileNames(); for (int i = 0, n = files.length; i < n; i++) { if( !files[i].contains(".wav")) { System.out.println(files[i]); } StringBuffer stringBuffer = new StringBuffer(); stringBuffer.append(fileDialog.getFilterPath()); if (stringBuffer.charAt(stringBuffer.length() - 1) != File.separatorChar) { stringBuffer.append(File.separatorChar); } stringBuffer.append(files[i]); stringBuffer.append(""); String finalName = stringBuffer.toString(); if( !finalName.contains(".wav")) { System.out.println(finalName); } result.add(finalName); } System.out.println(result.size()) ;

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  • Locking a file to verify a single execution of a service. How reliable?

    - by Camilo Díaz
    Hello, I am deploying a little service to an UNIX(AIX) system. I want to check if there is no active instance of that service running when starting it. How reliable is to implement that check like this? Try to acquire a lock on a file (w/ FileChannel) If succeeds, keep lock and continue execution If fails, exit and refuse to run the main body I am aware of software like the Tanuki wrapper, however, I'm longing for a simpler(maybe not portable) solution. Regarding PIDFILE(s): I want to avoid using them if possible, as I don't have administrative rights on the machine, neither knowledge in AIX's shell programming.

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  • JavaME FileConnection url

    - by Trimack
    Hi there, I want to save data to my Sony Ericsson K750i. I know the phone implements FileConnection version 1.0. The list of roots taken from FileSystemRegistry.listRoots(); returns single element named "c:/". I want to save a file.txt just about anywhere, but preferably to the memory stick attached. Unfortunately, it doesn't seem to work. It throws an IOException without any message. I tried opening the fileconnection on numerous roots like c:/, C:/, /, ./, root1/, SDCard/, CFCard/, MemoryStick/ and perhaps some more but without any luck. The exception is thrown right after this line for any of those roots: FileConnection filecon = (FileConnection) Connector.open("file:///MemoryStick/file.txt"); Please, what URL should i use?

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  • Does this Maven plugin really have an invalid descriptor?

    - by ovr
    COMMAND: mvn org.apache.maven.plugins:maven-archetype-plugin:2.0-alpha-4:generate -DarchetypeGroupId=org.beardedgeeks -DarchetypeArtifactId =gae-eclipse-maven-archetype -DarchetypeVersion=1.1.2 -DarchetypeRepository=http://beardedgeeks.googlecode.com/svn/repository/release s OUTPUT: [INFO] Scanning for projects... [INFO] ------------------------------------------------------------------------ [ERROR] BUILD ERROR [INFO] ------------------------------------------------------------------------ [INFO] Internal error in the plugin manager getting plugin 'org.apache.maven.plugins:maven-archetype-plugin': Plugin 'org.apache.maven .plugins:maven-archetype-plugin:2.0-alpha-4' has an invalid descriptor: 1) Plugin's descriptor contains the wrong group ID: net.kindleit 2) Plugin's descriptor contains the wrong artifact ID: maven-gae-plugin 3) Plugin's descriptor contains the wrong version: 0.5.9 [INFO] ------------------------------------------------------------------------ [INFO] For more information, run Maven with the -e switch [INFO] ------------------------------------------------------------------------ [INFO] Total time: < 1 second [INFO] Finished at: Wed Jun 09 20:48:35 CEST 2010 [INFO] Final Memory: 3M/15M [INFO] ------------------------------------------------------------------------ I have a hard time believing this Maven plugin has an invalid descriptor since other people seem to be using it with no problem. Am I doing something wrong?

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  • Indexing and Searching Over Word Level Annotation Layers in Lucene

    - by dmcer
    I have a data set with multiple layers of annotation over the underlying text, such as part-of-tags, chunks from a shallow parser, name entities, and others from various natural language processing (NLP) tools. For a sentence like The man went to the store, the annotations might look like: Word POS Chunk NER ==== === ===== ======== The DT NP Person man NN NP Person went VBD VP - to TO PP - the DT NP Location store NN NP Location I'd like to index a bunch of documents with annotations like these using Lucene and then perform searches across the different layers. An example of a simple query would be to retrieve all documents where Washington is tagged as a person. While I'm not absolutely committed to the notation, syntactically end-users might enter the query as follows: Query: Word=Washington,NER=Person I'd also like to do more complex queries involving the sequential order of annotations across different layers, e.g. find all the documents where there's a word tagged person followed by the words arrived at followed by a word tagged location. Such a query might look like: Query: "NER=Person Word=arrived Word=at NER=Location" What's a good way to go about approaching this with Lucene? Is there anyway to index and search over document fields that contain structured tokens?

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  • Where should I initialize variables for an OO Recursive Descent Parse Tree?

    - by Vasto
    I'd like to preface this by stating that this is for a class, so please don't solve this for me. One of my labs for my cse class is creating an interpreter for a BNF that was provided. I understand most of the concepts, but I'm trying to build up my tree and I'm unsure where to initialize values. I've tried in both the constructor, and in the methods but Eclipse's debugger still only shows the left branch, even though it runs through completely. Here is my main procedure so you can get an idea of how I'm calling the methods. public class Parser { public static void main(String[] args) throws IOException { FileTokenizer instance = FileTokenizer.Instance(); FileTokenizer.main(args); Prog prog = new Prog(); prog.ParseProg(); prog.PrintProg(); prog.ExecProg(); } Now here is My Prog class: public class Prog { private DeclSeq ds; private StmtSeq ss; Prog() { ds = new DeclSeq(); ss = new StmtSeq(); } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) // ds = new DeclSeq(); ds.ParseDS(); instance.skipToken(); //Skips begin (2) // ss = new StmtSeq(); ss.ParseSS(); instance.skipToken(); } I've tried having Prog() { ds = null; ss = null; } public void ParseProg() { FileTokenizer instance = FileTokenizer.Instance(); instance.skipToken(); //Skips program (1) ds = new DeclSeq(); ds.ParseDS(); ... But it gave me the same error. I need the parse tree built up so I can do a pretty print and an execute command, but like I said, I only get the left branch. Any help would be appreciated. Explanations why are even more so appreciated. Thank you, Vasto

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  • paintComponent on JPanel, image flashes and then disappears

    - by mark
    I have a JApplet (MainClass extends JApplet), a JPanel (ChartWindow extends JPanel) and a Grafico class. The problem is that the Grafico class instance has 2 JPanel that should show 2 images (1 for each panel) but the images are shown and after a little while they disappears: instead of them i get a gray background (like an empty JPanel). This happens for every repaint() call (that are made in the ChartWindow class) the MainClass init() contains chartwindow=new ChartWindow(); add(chartwindow) chartwindow has a Grafico instance. it's the ChartWindow's paintComponent (override) paintComponent(Graphics g) { super.paintComponent(g); Image immagineGrafico=createImage(grafico.pannelloGrafico.getWidth() ,grafico.pannelloGrafico.getHeight()); Image immagineVolumi=createImage(grafico.pannelloVolumi.getWidth() ,grafico.pannelloVolumi.getHeight()); Graphics2D imgGrafico=(Graphics2D)immagineGrafico.getGraphics(); Graphics2D imgVolumi=(Graphics2D)immagineVolumi.getGraphics(); grafico.draw(imgGrafico,imgVolumi,mouseX,mouseY); ((Graphics2D)grafico.pannelloGrafico.getGraphics()).drawImage(immagineGrafico,0,0,this); ((Graphics2D)grafico.pannelloVolumi.getGraphics()).drawImage(immagineVolumi,0,0,this); } grafico's JPanels are added this way in the ChartWindow's constructor grafico=new Grafico() ................ add(grafico.pannelloGrafico); add(grafico.pannelloVolumi); Tell me if you need more information, thank you very much :-)

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  • spring mvc forward to jsp

    - by jerluc
    I currently have my web.xml configured to catch 404s and send them to my spring controller which will perform a search given the original URL request. The functionality is all there as far as the catch and search go, however the trouble begins to arise when I try to return a view. <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver" p:order="1"> <property name="mediaTypes"> <map> <entry key="json" value="application/json" /> <entry key="jsp" value="text/html" /> </map> </property> <property name="defaultContentType" value="application/json" /> <property name="favorPathExtension" value="true" /> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver" /> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/" /> <property name="suffix" value="" /> </bean> </list> </property> <property name="defaultViews"> <list> <bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView" /> </list> </property> <property name="ignoreAcceptHeader" value="true" /> </bean> This is a snippet from my MVC config file. The problem lies in resolving the view's path to the /WEB-INF/jsp/ directory. Using a logger in my JBoss setup, I can see that when I test this search controller by going to a non-existent page, the following occurs: Server can't find the request Request is sent to 404 error page (in this case my search controller) Search controller performs search Search controller returns view name (for this illustration, we'll assume test.jsp is returned) Based off of server logger, I can see that org.springframework.web.servlet.view.JstlView is initialized once my search controller returns the view name (so I can assume it is being picked up correctly by the InternalResourceViewResolver) Server attempts to return content to browser resulting in a 404! A couple things confuse me about this: I'm not 100% sure why this isn't resolving when test.jsp clearly exists under the /WEB-INF/jsp/ directory. Even if there was some other problem, why would this result in a 404? Shouldn't a 404 error page that results in another 404 theoretically create an infinite loop? Thanks for any help or pointers! Controller class [incomplete]: @Controller public class SiteMapController { //-------------------------------------------------------------------------------------- @Autowired(required=true) private SearchService search; @Autowired(required=true) private CatalogService catalog; //-------------------------------------------------------------------------------------- @RequestMapping(value = "/sitemap", method = RequestMethod.GET) public String sitemap (HttpServletRequest request, HttpServletResponse response) { String forwardPath = ""; try { long startTime = System.nanoTime() / 1000000; String pathQuery = (String) request.getAttribute("javax.servlet.error.request_uri"); Scanner pathScanner = new Scanner(pathQuery).useDelimiter("\\/"); String context = pathScanner.next(); List<ProductLightDTO> results = new ArrayList<ProductLightDTO>(); StringBuilder query = new StringBuilder(); String currentValue; while (pathScanner.hasNext()) { currentValue = pathScanner.next().toLowerCase(); System.out.println(currentValue); if (query.length() > 0) query.append(" AND "); if (currentValue.contains("-")) { query.append("\""); query.append(currentValue.replace("-", " ")); query.append("\""); } else { query.append(currentValue + "*"); } } //results.addAll(this.doSearch(query.toString())); System.out.println("Request: " + pathQuery); System.out.println("Built Query:" + query.toString()); //System.out.println("Result size: " + results.size()); long totalTime = (System.nanoTime() / 1000000) - startTime; System.out.println("Total TTP: " + totalTime + "ms"); if (results == null || results.size() == 0) { forwardPath = "home.jsp"; } else if (results.size() == 1) { forwardPath = "product.jsp"; } else { forwardPath = "category.jsp"; } } catch (Exception ex) { System.err.println(ex); } System.out.println("Returning view: " + forwardPath); return forwardPath; } }

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  • Dynamically create and cast objects at runtime

    - by vaibhav bindroo
    Let's say we have 2 classes A and B public class A{ private int member1; A() { member1 = 10; } public getMember(){ return member1; } } Class B is also on the same lines except that its member variable is named member2 and gets intitialized to say 20 inside the constructor. My Requirement : At runtime , I get a string which contains a className ( could be A or B). I want to dynamically create an object of this class along with invoking the constructor. How can I achieve this . I don't want to use interfaces for common functionality of above classes Morever, later on I set the properties of this raw object using Propery Builder Bean Util class based on a list of columns . Class clazz = Class.forName("className"); Obj obj = clazz.newInstance(); How I can dynamically convert that obj to className object.

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • Which free and open source frameworks would you recommend for replacing which aspect of ATG

    - by Vihung
    ATG (http://www.atg.com) is a frameowrk, a platform and a solution for content presentation and management, personalisation, e-commerce and customer relationship management. Which free and open source frameworks or products would you recommend to replace the basic functionality it provides? In the spirit of Stack Overflow, can you answer with one item in each answer and use the voting rather than duplicating someone else's answer. I have started with some answers

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  • How to use an IN clause in iBATIS?

    - by furtelwart
    I'm using iBATIS to create select statements. Now I would like to implement the following SQL statement with iBATIS: SELECT * FROM table WHERE col1 IN ('value1', 'value2'); With the following approach, the statement is not prepared correctly and no result returns: SELECT * FROM table WHERE col1 IN #listOfValues#; iBATIS seems to restructure this list and tries to interpret it as a string. How can I use the IN clause correctly?

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