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  • Is it possible to apply inheritance to a Singleton class?

    - by Bragaadeesh
    Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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  • How can I force the server socket to re-accept a request from a client?

    - by Roman
    For those who does not want to read a long question here is a short version: A server has an opened socket for a client. The server gets a request to open a socket from the same client-IP and client-port. I want to fore the server not to refuse such a request but to close the old socket and open a new one. How can I do ti? And here is a long (original) question: I have the following situation. There is an established connection between a server and client. Then an external software (Bonjour) says to my client the it does not see the server in the local network. Well, client does nothing about that because of the following reasons: If Bonjour does not see the server it does not necessarily means that client cannot see the server. Even if the client trusts the Bonjour and close the socket it does not improve the situation ("to have no open socket" is worser that "to have a potentially bad socket"). So, client do nothing if server becomes invisible to Bonjour. But than the server re-appears in the Bonjour and Bonjour notify the client about that. In this situation the following situations are possible: The server reappears on a new IP address. So, the client needs to open a new socket to be able to communicate with the server. The server reappears on the old IP address. In this case we have two subcases: 2.1. The server was restarted (switched off and then switched on). So, it does not remember the old socket (which is still used by the client). So, client needs to close the old socket and open a new one (on the same server-IP address and the same server-port). 2.2. We had a temporal network problem and the server was running the whole time. So, the old socket is still available for the use. In this case the client does not really need to close the old socket and reopen a new one. But to simplify my life I decide to close and reopen the socket on the client side in any case (in spite on the fact that it is not really needed in the last described situation). But I can have problems with that solution. If I close the socket on the client side and than try to reopen a socket from the same client-IP and client-port, server will not accept the call for a new socket. The server will think that such a socket already exists. Can I write the server in such a way, that it does not refuse such calls. For example, if it (the server) sees that a client send a request for a socket from the same client-IP and client-port, it (server) close the available socket, associated with this client-IP and client-port and than it reopens a new socket.

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  • Trouble parsing self closing XML tags using SAX parser

    - by sandesh
    Hi, I am having trouble parsing self closing XML tags using SAX. I am trying to extract the link tag from the Google Base API.I am having reasonable success in parsing regular tags. Here is a snippet of the xml <entry> <id>http://www.google.com/base/feeds/snippets/15802191394735287303</id> <published>2010-04-05T11:00:00.000Z</published> <updated>2010-04-24T19:00:07.000Z</updated> <category scheme='http://base.google.com/categories/itemtypes' term='Products'/> <title type='text'>En-el1 Li-ion Battery+charger For Nikon Digital Camera</title> <link rel='alternate' type='text/html' href='http://rover.ebay.com/rover/1/711-67261-24966-0/2?ipn=psmain&amp;icep_vectorid=263602&amp;kwid=1&amp;mtid=691&amp;crlp=1_263602&amp;icep_item_id=170468125748&amp;itemid=170468125748'/> . . and so on I can parse the updates and published tags, but not the link and category tag. Here is my startElement and endElement overrides public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { if (qName.equals("title") && xmlTags.peek().equals("entry")) { insideEntryTitle = true; } xmlTags.push(qName); } public void endElement(String uri, String localName, String qName) throws SAXException { // If a "title" element is closed, we start a new line, to prepare // printing the new title. xmlTags.pop(); if (insideEntryTitle) { insideEntryTitle = false; System.out.println(); } } declaration for xmltags.. private Stack<String> xmlTags = new Stack<String>(); Any help guys? this is my first post here.. I hope I have followed posting rules! thanks a ton guys..

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  • NullPointerException when adding to BigDecimal

    - by Dan
    String[] toppings = new String[10]; BigDecimal toppingsPrice = null; toppings[0] = req.getParameter("extraCheese"); toppings[1] = req.getParameter("moreTomatoes"); toppings[2] = req.getParameter("extraOnions"); // ... for(int i = 0; i < toppings.length; i++) { if(toppings[i] != null) { toppingsPrice.add(new BigDecimal("0.99")); // <-- NPE is caused here. toppingsPrice = toppingsPrice.setScale(2, BigDecimal.ROUND_HALF_EVEN); } } I am getting a NullPointerException in the above code when adding 0.99 to toppingsPrice. I am working with money values, so I have used BigDecimal. Is there something wrong with how I am adding the 0.99c price?

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  • Implementing Unowned relationship Google App Engine

    - by nwallman
    My question is more of a best practices question on how to implement unowned relationships with Google App Engine. I am using JDO to do my persistence and like recommended in the google docs I'm persisting my list of unowned relationships like so: @PersistenceCapable(identityType = IdentityType.APPLICATION) public class User implements Serializable, UserDetails { ... @Persistent private List<Key> groups; ... } Now I came across my predicament when I went to query that list of objects using they Key object. So when I get my list of group keys in order to actually return a list of Group objects I have to do a look up on that key to get the object. My question is what is the recommended way of doing a unowned look up on a model object? Should I have an instance of the PersistanceManagerFactory on my Model object so I can do a lookup? Should I have an instance of my GroupDAO object on my Model object so I can do a look up? Should I have a Utility to do this type of lookup? I'm new to this so I just want to know which is the best way to do this. Thanks.

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  • Batch insert mode with hibernate and oracle: seems to be dropping back to slow mode silently

    - by Chris
    I'm trying to get a batch insert working with Hibernate into Oracle, according to what i've read here: http://docs.jboss.org/hibernate/core/3.3/reference/en/html/batch.html , but with my benchmarking it doesn't seem any faster than before. Can anyone suggest a way to prove whether hibernate is using batch mode or not? I hear that there are numerous reasons why it may silently drop into normal mode (eg associations and generated ids) so is there some way to find out why it has gone non-batch? My hibernate.cfg.xml contains this line which i believe is all i need to enable batch mode: <property name="jdbc.batch_size">50</property> My insert code looks like this: List<LogEntry> entries = ..a list of 100 LogEntry data classes... Session sess = sessionFactory.getCurrentSession(); for(LogEntry e : entries) { sess.save(e); } sess.flush(); sess.clear(); My 'logentry' class has no associations, the only interesting field is the id: @Entity @Table(name="log_entries") public class LogEntry { @Id @GeneratedValue public Long id; ..other fields - strings and ints... However, since it is oracle, i believe the @GeneratedValue will use the sequence generator. And i believe that only the 'identity' generator will stop bulk inserts. So if anyone can explain why it isn't running in batch mode, or how i can find out for sure if it is or isn't in batch mode, or find out why hibernate is silently dropping back to slow mode, i'd be most grateful. Thanks

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  • Connection Pooling in J2SE?

    - by Zombies
    It is hard to find a resource on this without finding J2EE, but here is what I am looking for: All I have is a standard J2SE app, it makes a lot of DB connections. I simply need to make use of a connection pool. Any suggestions?

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  • issue of JSTL forEach iterate from arrayList

    - by Mickey
    In my code, I have used ArrayList which stores the number format like '$0.00 to $1,000,000.00' in each index of array list. while iterate in JSP through tag, its values are printing like $0.00 to $1 as a first string, 000 as a second string and 000.00 as a thrid string. but it has to print like '$0.00 to $1,000,000.00'. what will be the problem is? Thanks in advance

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  • Triggering Quartz job from JSF (Any front end)- How to wait for the job execution to be over

    - by Maximus
    I am developing a front end to trigger a quartz job on the fly. I have a form in the JSF page whose click action will dynamically trigger a quartz job. The job is invoked by the following statement, the job is triggered and everything works fine. scheduler.triggerJob("Job1",Scheduler.DEFAULT_GROUP,jobDataMap); From what I understand the job seems to run in a separate thread and the execution of the calling function does not wait for the job to be over. Since I am invoking the job from front end, I would like to wait till the job is over before I navigate to a different JSF page. So I can display an error message if the job fails. I would also like to display a message to the user, "Processing job, please wait.." until the job is actually over. Any ideas on how to accomplish this will be appreciated. Thanks !

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  • Projections.count() and Projections.countDistinct() both result in the same query

    - by Kim L
    EDIT: I've edited this post completely, so that the new description of my problem includes all the details and not only what I previously considered relevant. Maybe this new description will help to solve the problem I'm facing. I have two entity classes, Customer and CustomerGroup. The relation between customer and customer groups is ManyToMany. The customer groups are annotated in the following way in the Customer class. @Entity public class Customer { ... @ManyToMany(mappedBy = "customers", fetch = FetchType.LAZY) public Set<CustomerGroup> getCustomerGroups() { ... } ... public String getUuid() { return uuid; } ... } The customer reference in the customer groups class is annotated in the following way @Entity public class CustomerGroup { ... @ManyToMany public Set<Customer> getCustomers() { ... } ... public String getUuid() { return uuid; } ... } Note that both the CustomerGroup and Customer classes also have an UUID field. The UUID is a unique string (uniqueness is not forced in the datamodel, as you can see, it is handled as any other normal string). What I'm trying to do, is to fetch all customers which do not belong to any customer group OR the customer group is a "valid group". The validity of a customer group is defined with a list of valid UUIDs. I've created the following criteria query Criteria criteria = getSession().createCriteria(Customer.class); criteria.setProjection(Projections.countDistinct("uuid")); criteria = criteria.createCriteria("customerGroups", "groups", Criteria.LEFT_JOIN); List<String> uuids = getValidUUIDs(); Criterion criterion = Restrictions.isNull("groups.uuid"); if (uuids != null && uuids.size() > 0) { criterion = Restrictions.or(criterion, Restrictions.in( "groups.uuid", uuids)); } criteria.add(criterion); When executing the query, it will result in the following SQL query select count(*) as y0_ from Customer this_ left outer join CustomerGroup_Customer customergr3_ on this_.id=customergr3_.customers_id left outer join CustomerGroup groups1_ on customergr3_.customerGroups_id=groups1_.id where groups1_.uuid is null or groups1_.uuid in ( ?, ? ) The query is exactly what I wanted, but with one exception. Since a Customer can belong to multiple CustomerGroups, left joining the CustomerGroup will result in duplicated Customer objects. Hence the count(*) will give a false value, as it only counts how many results there are. I need to get the amount of unique customers and this I expected to achieve by using the Projections.countDistinct("uuid"); -projection. For some reason, as you can see, the projection will still result in a count(*) query instead of the expected count(distinct uuid). Replacing the projection countDistinct with just count("uuid") will result in the exactly same query. Am I doing something wrong or is this a bug? === "Problem" solved. Reason: PEBKAC (Problem Exists Between Keyboard And Chair). I had a branch in my code and didn't realize that the branch was executed. That branch used rowCount() instead of countDistinct().

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  • How can I change jtable height at runtime

    - by wniroshan
    I hava a JFrame with multiple JPanels of similar width aligned one below other. I use one of these JPanels to display a JTable which is the last JPanel of the lot. This JPanel has a JScrollpane as a child component. This is where I try to add my table dynamically. Initial height of this JScrollpane is set to 40. I designed above template using Netbeans 6.8 Now I'm trying to add the table to the JPanel. When a button is pressed below code snippet is called. The class which includes this code extends javax.swing.JFrame class. I am expecting below code would adjust table height according to the row count and display the table. SearchTable = new JTable(RowData, DisplayNames) { @Override public boolean isCellEditable(int rowIndex, int vColIndex) { return false; } }; // if row count is less than 10 then display all the rows without a scroll bar if (SearchTable.getRowCount() < 10) { pnl_tblpanel.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (SearchTable.getRowCount() + 4))); scr_tblholder.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (SearchTable.getRowCount() + 4))); } else {// if row count is more than 10 display first 10 rows and add a scroll bar pnl_tblpanel.setPreferredSize(new Dimension(625, SearchTable.getRowHeight() * (10 + 2))); scr_tblholder.setAutoscrolls(true); } //pnl_tblpanel.add(scr_tblholder); scr_tblholder.setViewportView(SearchTable); //pnl_tblpanel.repaint(); pnl_tblpanel.validate(); this.validate(); //this.repaint(); pnl_tblpanel.setVisible(true); this.pack(); The table displays, but the table height is not changed according to the row count. It stays its default value. I have been trying many combinations of validate and repaint but nothing worked. (More in desperation) Can anyone shed some light on this Thank you

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  • "Detecting" and loading of "plugins" in GAE

    - by Patrick Cornelissen
    Hi! I have a "plugin like" architecture and I want to create one instance of each class that implements a dedicated interface and put these in a cache. (To have a singleton-ish effect). The plugins will be provided as jars and put into the app engine war file before the app is uploaded. I have tried to use the ClassPathScanningCandidateComponentProvider as I'm using spring anyway, but this didn't work. The provider complained that it was not able to find the HttpServletResponse class file while scanning the classpath. I can't get around this, when I add the servlet jar, then I'll get of course problems, because the same jar is also provided by the GAE. If I don't, I'm getting the error above... So I tried to add a static initialization code, but of course this doesn't work, because the class is initialized when it's instantiated for the first time. (Well I knew that but it was worth a try) The last chance I currently see is that I create a properties file with all plugin classes when the package is created, but this requires writing of a maven plugin etc. and I'd like to avoid that. Is there something that I am missing?

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  • Is it possible to optimize maven dependencies automatically?

    - by AlexR
    I am working on a big project that consists of about 40 sub-projects with very not optimized dependencies. There are declared dependencies that are not in use as well as used but undeclared dependencies. The second case is possible when dependency is added via other dependency. I want to remove redundant and add required dependencies. I ran mvn dependency:analyze and got a long list of warnings I have to fix now. I wonder whether there is maven plugin or any other utility that can update my pom.xml files automatically. I tried to do it manually but it takes a lot of time. It seems it will take a couple of days of copy/paste to complete the task. In worse case I can write such script myself but probably ready stuff exists? Here is how mvn dependency:analyze reports dependency warnings: [WARNING] Used undeclared dependencies found: [WARNING] org.apache.httpcomponents:httpcore:jar:4.1:compile [WARNING] Unused declared dependencies found: [WARNING] commons-lang:commons-lang:jar:2.4:compile [WARNING] org.json:json:jar:20090211:compile

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  • How to use @BeforeClass and @AfterClass in JunitPerf?

    - by allenzzzxd
    Hi, I want to do some actions before the whole test suite (also after the suite). So I wrote like: public class PerformanceTest extends TestCase { @BeforeClass public static void suiteSetup() throws Exception { //do something } @AfterClass public static void suiteSetup() throws Exception { //do something } @Before public void setUp() throws Exception { //do something } @After public void tearDown() throws Exception { //do something } public PerformanceTest(String testName){ super(testName); } public static Test suite() { TestSuite suite = new TestSuite(); Test testcase1 = new PerformanceTest("DoTest1"); Test loadTest1 = new LoadTest(testcase1, n); Test testcase2 = new PerformanceTest("DoTest2"); Test loadTest2 = new LoadTest(testcase2, n); } public void DoTest1 throws Throwable{ //do something } public void DoTest2 throws Throwable{ //do something } } But I found that it never reach the code in @BeforeClass and @AfterClass. So how could I do to solve this problem? Or is there other way to realize this? Thank you for your help.

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  • Contacts & Autocomplete

    - by Vince
    First post. I'm new to android and programming in general. What I'm attempting to is to have an autocomplete text box pop up with auto complete names from the contact list. IE, if they type in "john" it will say "John Smith" or any john in their contacts. The code is basic, I pulled it from a few tutorials. private void autoCompleteBox() { ContentResolver cr = getContentResolver(); Uri contacts = Uri.parse("content://contacts/people"); Cursor managedCursor1 = cr.query(contacts, null, null, null, null); if (managedCursor1.moveToFirst()) { String contactname; String cphoneNumber; int nameColumn = managedCursor1.getColumnIndex("name"); int phoneColumn = managedCursor1.getColumnIndex("number"); Log.d("int Name", Integer.toString(nameColumn)); Log.d("int Number", Integer.toString(phoneColumn)); do { // Get the field values contactname = managedCursor1.getString(nameColumn); cphoneNumber = managedCursor1.getString(phoneColumn); if ((contactname != " " || contactname != null) && (cphoneNumber != " " || cphoneNumber != null)) { c_Name.add(contactname); c_Number.add(cphoneNumber); Toast.makeText(this, contactname, Toast.LENGTH_SHORT) .show(); } } while (managedCursor1.moveToNext()); } name_Val = (String[]) c_Name.toArray(new String[c_Name.size()]); phone_Val = (String[]) c_Number.toArray(new String[c_Name.size()]); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, name_Val); personName.setAdapter(adapter); } personName is my autocompletetextbox. So it actually works when I use it in the emulator (4.2) with manually entered contacts through the people app, but when I use it on my device, it will not pop up with any names. I'm sure it's something ridiculous but I've tried to find the answer and I'm getting nowhere. Can't learn if I don't ask.

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  • creating and returning an array from a method

    - by Troy
    howdy, i currently have a method that checks what is around the centre item in a 3x3 grid, if what is in the 8 adjacent positions is containing what i am checking for i want to mark that square on an array with length 7 as being 1. to do this i need to create and return an array in my method, is it possible to do this?

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