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  • Doubt in abstract classes

    - by mohit
    public abstract class Person { private String name; public Person(String name) { this.name = name; System.out.println("Person"); } public String getName() { return name; } abstract public String getDescription(); } public class Student extends Person { private String major; public Student(String name, String major) { super(name); this.major = major; } public String getMajor() { return major; } @Override public String getDescription() { return "student" + super.getName() + " having" + major; } } public class PersonTest { public static void main(String[] args) { Person person = new Student("XYZ", "ABC"); System.out.println(person.getDescription()); } } Ques: We cannot create objects of abstract classes, then why Person Constructor has been invoked, even its an abstract class?

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  • about Sorting Algorithms

    - by matin1234
    Hi I want to know that we always use Sorting algorithm like (Insertion Sort or Merge Sort,...) just for lists and arrays?? and we do not use these algorithms for stack or queue ??? thanks

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  • How to re-order a List<String>

    - by tarka
    I have created the following method: public List<String> listAll() { List worldCountriesByLocal = new ArrayList(); for (Locale locale : Locale.getAvailableLocales()) { final String isoCountry = locale.getDisplayCountry(); if (isoCountry.length() > 0) { worldCountriesByLocal.add(isoCountry); Collections.sort(worldCountriesByLocal); } } return worldCountriesByLocal; } Its pretty simple and it returns a list of world countries in the users locale. I then sort it to get it alphabetic. This all works perfectly (except I seem to occasionally get duplicates of countries!). Anyway, what I need is to place the US, and UK at the top of the list regardless. The problem I have is that I can't isolate the index or the string that will be returned for the US and UK because that is specific to the locale! Any ideas would be really appreciated.

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  • This code is not submitting to a form? Why

    - by Ankur
    Since I am using get I expect to see the submitted values appended to the queryString but instead all I see is the URL of the servlet being called with nothing added at the end. <form id="editClassList" name="editClassList" method="get" action="EditClassList"> <% HashMap<Integer,String> classes = new HashMap<Integer,String>(); classes = (HashMap<Integer,String>) request.getAttribute("classes"); %> <% if(classes.size()==0){ %> <label><input class="small-link" type="text" id="add-this-class" size="42" value="" /></label> <% } %> <% Set<Integer> classIds = new HashSet<Integer>(); classIds = classes.keySet(); Iterator<Integer> itr = classIds.iterator(); while(itr.hasNext()){ int nextId = (Integer)itr.next(); %> <label><input class="small-link" type="text" id="<% out.print(nextId); %>" size="42" value="<% out.print(classes.get(nextId)); %>" /> </label> <img id="add-class" src="images/add.png" width="16" height="16" /><br /> <label><input class="small-link" type="text" id="class-to-add" size="42" value="" /></label> <% } %> <label><input type="submit" id="save-class-btn" value="Save Class(es)" /></label> </form>

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  • Multi-Threaded Application - Help with some pseudo code!!

    - by HonorGod
    I am working on a multi-threaded application and need help with some pseudo-code. To make it simpler for implementation I will try to explain that in simple terms / test case. Here is the scenario - I have an array list of strings (say 100 strings) I have a Reader Class that reads the strings and passes them to a Writer Class that prints the strings to the console. Right now this runs in a Single Thread Model. I wanted to make this multi-threaded but with the following features - Ability to set MAX_READERS Ability to set MAX_WRITERS Ability to set BATCH_SIZE So basically the code should instantiate those many Readers and Writers and do the work in parallel. Any pseudo code will really be helpful to keep me going!

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  • can a .class file be added to the urlpath of a URLClassLoader

    - by java_geek
    I have a custom class loader which extends from a URLClassLoader. I added a .class file to the urlpath using addURL(); but when i do a class.forname() using this loader i get a ClassNotFoundException. However, if i create a jar and add the jar to the urlpath, i do not get any exception. What can be added to the urlpath of a URLClassLoader usign addURL()

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  • Reflection: take values from an unknown running alpplication

    - by Dr.Lesh
    I'm writing an application that searchs for Semaphore types in the fields of unknown classes in unknown application (passed by user). I made it using Reflection and it worked. Now I want to fill up these semaphores with values, taking them from a running instance of this unknown application. So i took the class with "main" method of this unknown application, made a newInstance, and passed it when invoking the main method to start the application: Class mainClass = getItSomeWhere(); Object instance = mainClass.newInstance(); Method mainMethod = mainClass.getDeclaredMethod("main", new Class[]{String[].class}); mainMethod.invoke(instance, new Object[]{args}); and it worked fine. Now, how can I get the semaphore values, taking them from the classes of this running application, when I only have an instance of the main class? Many thanks for the answers.

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  • Decorator Pattern - Multiple wrappers or quantity property?

    - by Jiminizer
    I'm making use of the decorator pattern for one of the first times, as part of a Uni project. As far as I can see, the pattern seems to be meant more for adding functionality in a modular manner, however we've been taught it with uses such as a coffee or pizza maker, where the object has modular components that are added - changing properties rather than behaviour. I'm trying to make the most of both uses, however I've come up with a question. In the example in the book we're using (Head First Design Patterns), the pattern is used in a coffee shop creating different coffees. So, for example, milk, froth, sugar, sprinkles are all decorators. How would you implement a system that used the same decorator multiple times (for example, a coffee with two sugars)? Would you rewrap the coffee, or give sugar a quantity property? Or (as i'm starting to suspect) would this never be an issue as the pattern isn't designed to be used this way?

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  • Loading child entities with JPA on Google App Engine

    - by Phil H
    I am not able to get child entities to load once they are persisted on Google App Engine. I am certain that they are saving because I can see them in the datastore. For example if I have the following two entities. public class Parent implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; @OneToMany(cascade=CascadeType.ALL) private List<Child> children = new ArrayList<Child>(); //getters and setters } public class Child implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String key; private String name; @ManyToOne private Parent parent; //getters and setters } I can save the parent and a child just fine using the following: Parent parent = new Parent(); Child child = new Child(); child.setName("Child Object"); parent.getChildren().add(child); em.persist(parent); However when I try to load the parent and then try to access the children (I know GAE lazy loads) I do not get the child records. //parent already successfully loaded parent.getChildren.size(); // this returns 0 I've looked at tutorial after tutorial and nothing has worked so far. I'm using version 1.3.3.1 of the SDK. I've seen the problem mentioned on various blogs and even the App Engine forums but the answer is always JDO related. Am I doing something wrong or has anyone else had this problem and solved it for JPA?

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  • abstract class need acces to subclass atribute

    - by user1742980
    I have a problem with my code. public abstract class SimplePolygon implements Polygon { ... public String toString(){ String str = "Polygon: vertices ="; for(int i = 0;i<varray.length;i++){ str += " "; str += varray[i]; } return str; } } public class ArrayPolygon extends SimplePolygon { private Vertex2D[] varray; public ArrayPolygon(Vertex2D[] array){ varray = new Vertex2D[array.length]; if (array == null){} for(int i = 0;i<array.length;i++){ if (array[i] == null){} varray[i] = array[i]; } ... } Problem is, that i'm not allowed to add any atribute or method to abstract class SimplePolygon, so i'cant properly initialize varray. It could simply be solved with protected atrib in that class, but for some (stupid) reason i'cant do that. Has anybody an idea how to solve it without that? Thanks for all help.

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  • Create a custom menu for BlackBerry

    - by Dachmt
    Hi I'm a beginner in BlackBerry programming, I need to replace in my application the default menu (when you press the menu button) by a custom menu, horizontal. The best to describe is I want the same result as the WeatherEye application for BlackBerry... I know how to create the default menu, but this one I have no idea! Thank you,

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  • Compare Date objects with different levels of precision

    - by brainimus
    I have a JUnit test that fails because the milliseconds are different. In this case I don't care about the milliseconds. How can I change the precision of the assert to ignore milliseconds (or any precision I would like it set to)? Example of a failing assert that I would like to pass: Date dateOne = new Date(); dateOne.setTime(61202516585000L); Date dateTwo = new Date(); dateTwo.setTime(61202516585123L); assertEquals(dateOne, dateTwo);

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  • ANDROID : how to get value stored in ArrayList<HashMap<key,value>>?

    - by Roshni Kyada
    I have ArrayList. At another activity i want to access all values stored in ArrayList. I tried following code. ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>(); for(Hashmap<String, String> map: mylist) { for(Entry<String, String> mapEntry: map) { String key = mapEntry.getKey(); String value = mapEntry.getValue(); } } but it shows an error at for(Entry mapEntry: map) that it only interate over Array.

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  • Distributed Cache with Serialized File as DataStore in Oracle Coherence

    - by user226295
    Weired but I am investigating the Oracle Coherence as a substitue for distribute cache. My primarr problem is that we dont have distribituted cache as such as of now in our app. Thats my major concern. And thats what I want to implement. So, lets say if I take up a machine and start a new (3rd) reading process, it will be able to connect to the cache and listen to the cache and will have a full set of cache triplicated (as of now its duplicated) Now thats waste from a common person stanpoint too. The size of the cache is 2 GB and without going distibuted its limiting us. Thats bring me to Coheremce. But now, we dont have database as persistent store too. we have the archival processes as our persistent store. (90 days worth of data) Ok now multiply that with soem where around 2 GB * 90 (thats the bare minimum we want to keep). Preliminary/Intermediate analysis of Coherence as a solution. And a (supposedly) brilliant thought crossed my mind. Why not have this as persistant storage with my distributed cache. Does Oracle Coherence support that. I will get rid of archiving infrastructure too (i hate daemon archiving processes). For some starnge reasons, I dont wanna go to the DB to replace those flat files. What say?, can Coherence be my savior? Any other stable alternate too. (Coherence is imposed on me by big guys, FYI)

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  • Flickering when repainting a JPanel inside a JScrollPAne

    - by pR0Ps
    I'm having a problem with repainting a JPanel inside a JScrollPane. Basically, I'm just trying to 'wrap' my existing EditPanel (it originally extended JPanel) into a JScrollPane. It seems that the JPanel updates too often (mass flickering). How would I stop this from happening? I tried using the setIgnoreRepaint() but it didn't seem to do anything. Will this current implementation work or would I need to create another inner class to fine-tune the JPanel I'm using to display graphics? Skeleton code: public class MyProgram extends JFrame{ public MyProgram(){ super(); add(new EditPanel()); pack(); } private class EditPanel extends JScrollPane{ private JPanel graphicsPanel; public EditPanel(){ graphicsPanel = new JPanel(); } public void paintComponent(Graphics g){ graphicsPanel.revalidate(); //update the scrollpane to current panel size repaint(); Graphics g2 = graphicsPanel.getGraphics(); g2.drawImage(imageToDraw, 0, 0, null); } } }

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  • JTA Transaction: What happens if an exception happens but rollback is not called on the transaction?

    - by kellyfj
    We have some third party code wherein they do the following 1) Create a User Transaction e.g. txn = (UserTransaction)ctx.lookup( "UserTransaction" ); txn.begin( ); 2) Do some work persisting to the database (via JPA) to a MySQL database 3) txn.commit() They have Exception blocks but NONE of them call txn.rollback. Good coding practice says they NEED to call rollback if an exception occurs but my question is If the txn is not commited, and an exception occurs what is the negative effect of them NOT calling rollback?

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  • 3D array initialization

    - by xdevel2000
    I need to represent some spatial points: x,y,z when I try to initialize the array like this: int[][][] points { { {100, 120, 10}, {100, 120, 18}, ... } } I got an error: Uncompilable source code - not a statement where is the error?

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  • Is this a correct way to stop Execution Task

    - by Yan Cheng CHEOK
    I came across code to stop execution's task. private final ExecutorService executor = Executors.newSingleThreadExecutor(); public void stop() { executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (!Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; } I realize that, it is possible for Runnable to be in forever loop, as Unknown fun may Thread.sleep, clear the interrupt flag and ignore the InterruptedException Unknown fun may Thread.interrupted, clear the interrupt flag. I was wondering, is the following way correct way to fix the code? private final ExecutorService executor = Executors.newSingleThreadExecutor(); private volatile boolean flag = true; public void stop() { flag = false; executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (flag && !Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; }

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  • JDBC Connection pool monitoring GlassFish

    - by john
    I am trying to find a setting by which the connection pool monitoring information would come in the server.log whenever an error like "error allocating a connection" or "connection closed" occur. I found some blog entries that talk about this but they mention it from GUI prespective. However, I want a setting on the connection pool itself so that perodically the connection pool monitoring information would be shown in the logs. Does anyone know of such a setting? On Sun app Server 8.X it used to be perf-monitor

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  • how to log digester with apache commons?

    - by Bruce
    Hi all I'm having trouble getting digester to log anything. I'd be hugely grateful for any light anyone can shed. In my code I'm doing this: Digester digester = new Digester(); .. some digester set up stuff // What on earth should go in here???? digester.setLogger(LogFactory.getLog("org.apache.commons.logging.Log")); I have a commons-logging.properties file in my classpath as follows: org.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog org.apache.commons.logging.simplelog.log.org.apache.commons.digester.Digester=debug org.apache.commons.logging.simplelog.log.org.apache.commons.digester.Digester.sax=info I just get no debug info at all.. Thanks for your help!

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