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  • Returning an anonymous class that uses a final primitive. How does it work?

    - by Tim P
    Hi, I was wondering if someone could explain how the following code works: public interface Result { public int getCount(); public List<Thing> getThings(); } class SomeClass { ... public Result getThingResult() { final List<Thing> things = .. populated from something. final int count = 5; return new Result { @Override public int getCount() { return count; } @Override public List<Thing> getThings(); return things; } } } ... } Where do the primitive int , List reference and List instance get stored in memory? It can't be on the stack.. so where? Is there a difference between how references and primitives are handled in this situation? Thanks a bunch, Tim P.

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  • The fastest way to do a collection subtraction

    - by Tony
    I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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  • Creating a bitmask parameter for a function or method

    - by synic
    I noticed a lot of Android functions have a parameter that you can pass in that's a bitmask, for different options, like on PendingIntent, you can pass in things like you can call getActivity() with PendingIntent.FLAG_CANCEL_CURRENT|PendingIntent.FLAG_NO_CREATE. I'm wondering how I can create a function that has a parameter like this?

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  • How to keep the session of user login?

    - by YaW
    Hi, I have an app that requires user to register. I've got the app conected to PHP in my server to do the logic of register/login and so, this is not problem at all. But, I want to keep a session of the user in local, so the user doesn't have to login again every time he runs the app. So, I want something like this: First time user, he opens the app, register and login. Do some stuff with the app and closes it. Open the app again, the user is recognized so he doesn't need to login again. I only need to store an ID and a Username (both fetched from the DB in the login php method). What's the best way to do this?? I've thought about doing a custom preference, store the data in files or even a local DB (sqlite). Any suggestions?

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  • Best practice for DAO pattern ?

    - by Tony
    I've seen a lot of codes use a service-dao pattern , I don't know the origin of this pattern . It force the front layer call service , then delegates some of the service task to dao. I want to ask : Does DAO layer do purely data access related task ? What about exception encapsulation ? Is there other pattern can be used to replace this ?

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  • Guide to Learn J2ME

    - by Sopolin
    Hi all, I am starting study java2me. But I have some source study about it like ebook, source sample code, and ... Could anybody give some link website or source ebook study about it. Thanks, Sopolin

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  • JPA optimistic lock - setting @Version to entity class cause query to include VERSION as column

    - by masato-san
    I'm using JPA Toplink Essential, Netbean6.8, GlassFish v3 In my Entity class I added @Version annotation to enable optimistic locking at transaction commit however after I added the annotation, my query started including VERSION as column thus throwing SQL exception. None of this is mentioned in any tutorial I've seen so far. What could be wrong? Snippet public class MasatosanTest2 implements Serializable { private static final long serialVersionUID = 1L; @Id @Basic(optional = false) @Column(name = "id") private Integer id; @Column(name = "username") private String username; @Column(name = "note") private String note; //here adding Version @Version int version; query used: SELECT m FROM MasatosanTest2 m Internal Exception: com.microsoft.sqlserver.jdbc.SQLServerException Call: SELECT id, username, note, VERSION FROM MasatosanTest2

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  • Exception thrown while working with JTabbedPane

    - by Halo
    I'm using a JTabbedPane in my application and I listen to its changes with ChangeListener so that I can know which tab is currently selected. So my stateChanged method is; public void stateChanged(ChangeEvent e) { currentPageIndex = jTabbedPane.getSelectedIndex(); } But while I'm adding new tabs to the JTabbedPane it throws an ArrayIndexOutOfBoundsException in the method above, I don't know why. Some suggested for a similar case that this is a bug http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4873983, but as you'll see some says the solution is to work with Swing from EventDispatchThread. What does it mean, do they mean the SwingUtilities.invokeLater thing? Can someone show me how I can modify my stateChanged method accordingly to avoid the exception?

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  • How to determine which source files are required for an Eclipse run configuration

    - by isme
    When writing code in an Eclipse project, I'm usually quite messy and undisciplined in how I create and organize my classes, at least in the early hacky and experimental stages. In particular, I create more than one class with a main method for testing different ideas that share most of the same classes. If I come up with something like a useful app, I can export it to a runnable jar so I can share it with friends. But this simply packs up the whole project, which can become several megabytes big if I'm relying on large library such as httpclient. Also, if I decide to refactor my lump of code into several projects once I work out what works, and I can't remember which source files are used in a particular run configuration, all I can do it copy the main class to a new project and then keep copying missing types till the new project compiles. Is there a way in Eclipse to determine which classes are actually used in a particular run configuration? EDIT: Here's an example. Say I'm experimenting with web scraping, and so far I've tried to scrape the search-result pages of both youtube.com and wrzuta.pl. I have a bunch of classes that implement scraping in general, a few that are specific to each of youtube and wrzuta. On top of this I have a basic gui common to both scrapers, but a few wrzuta- and youtube-specific buttons and options. The WrzutaGuiMain and YoutubeGuiMain classes each contain a main method to configure and show the gui for each respective website. Can Eclipse look at each of these to determine which types are referenced?

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  • How can i take only integer input from keyboard and if input is invalid how do i ask user agaian

    - by fari
    This is what i have written so far but when exception is raised it does not again ask teh user for input. do{ System.out.println("Enter the number of stones to play with: "); BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String temp=br.readLine(); }while (key<0 && key>9); if(key<0 || key>10) throw new InvalidStartingStonesException(key); player1=new KeyBoardPlayer(); player2 = new KeyBoardPlayer(); this.player1=player1; this.player2=player2; state=new KalaGameState(key); } catch(NumberFormatException nFE) { System.out.println("Not an Integer");} catch(IOException e) { System.out.println(e); }

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  • How to make Spring accept non-void setters?

    - by Chris
    Hi, I have an API which I am turning into an internal DSL. As such, most methods in my PoJos return a reference to this so that I can chain methods together declaratively as such (syntactic sugar). myComponent .setID("MyId") .setProperty("One","1") .setProperty("Two","2") .setAssociation(anotherComponent) .execute(); My API does not depend on Spring but I wish to make it 'Spring-Friendly' by being PoJo friendly with zero argument constructors, getters and setters. The problem is that Spring seems to not detect my setter methods when I have a non-void return type. The return type of this is very convenient when chaining together my commands so I don't want to destroy my programmatic API just be to compatible with Spring injection. Is there a setting in Spring to allow me to use non-void setters? Chris

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  • Throwing exception vs returning null value with switch statement

    - by Greg
    So I have function that formats a date to coerce to given enum DateType{CURRENT, START, END} what would be the best way to handling return value with cases that use switch statement public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... default:throw new ("Something strange happend"); } } OR throw excpetion at the end public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } //It will never reach here, just to make compiler happy throw new IllegalArgumentException("Something strange happend"); } OR return null public static String format(Date date, DateType datetype) { ..validation checks switch(datetype){ case CURRENT:{ return getFormattedDate(date, "yyyy-MM-dd hh:mm:ss"); } ... } return null; } What would be the best practice here ? Also all the enum values will be handled in the case statement

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  • Generating a error code per property in Hibernate validator

    - by Mike Q
    Hi all, I am looking at using hibernate validator for a requirement of mine. I want to validate a bean where properties may have multiple validation checks. e.g. class MyValidationBean { @NotNull @Length( min = 5, max = 10 ) private String myProperty; } But if this property fails validation I want a specific error code to be associated with the ConstraintViolation, regardless of whether it failed because of @Required or @Length, although I would like to preserve the error message. class MyValidationBean { @NotNull @Length( min = 5, max = 10 ) @ErrorCode( "1234" ) private String myProperty; } Something like the above would be good but it doesn't have to be structured exactly like that. I can't see a way to do this with hibernate validator. Is it possible? Thanks.

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  • Swing: Scroll to bottom of JScrollPane, conditional on current viewport location

    - by I82Much
    Hi all, I am attempting to mimic the functionality of Adium and most other chat clients I've seen, wherein the scrollbars advance to the bottom when new messages come in, but only if you're already there. In other words, if you've scrolled a few lines up and are reading, when a new message comes in it won't jump your position to the bottom of the screen; that would be annoying. But if you're scrolled to the bottom, the program rightly assumes that you want to see the most recent messages at all times, and so auto-scrolls accordingly. I have had a bear of a time trying to mimic this; the platform seems to fight this behavior at all costs. The best I can do is as follows: In constructor: JTextArea chatArea = new JTextArea(); JScrollPane chatAreaScrollPane = new JScrollPane(chatArea); // We will manually handle advancing chat window DefaultCaret caret = (DefaultCaret) chatArea.getCaret(); caret.setUpdatePolicy(DefaultCaret.NEVER_UPDATE); In method that handles new text coming in: boolean atBottom = isViewAtBottom(); // Append the text using styles etc to the chatArea if (atBottom) { scrollViewportToBottom(); } public boolean isAtBottom() { // Is the last line of text the last line of text visible? Adjustable sb = chatAreaScrollPane.getVerticalScrollBar(); int val = sb.getValue(); int lowest = val + sb.getVisibleAmount(); int maxVal = sb.getMaximum(); boolean atBottom = maxVal == lowest; return atBottom; } private void scrollToBottom() { chatArea.setCaretPosition(chatArea.getDocument().getLength()); } Now, this works, but it's janky and not ideal for two reasons. By setting the caret position, whatever selection the user may have in the chat area is erased. I can imagine this would be very irritating if he's attempting to copy/paste. Since the advancement of the scroll pane occurs after the text is inserted, there is a split second where the scrollbar is in the wrong position, and then it visually jumps towards the end. This is not ideal. Before you ask, yes I've read this blog post on Text Area Scrolling, but the default scroll to bottom behavior is not what I want. Other related (but to my mind, not completely helpful in this regard) questions: Setting scroll bar on a jscrollpane Making a JScrollPane automatically scroll all the way down. Any help in this regard would be very much appreciated.

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  • About Data Objects and DAO Design when using Hibernate

    - by X. Ma
    I'm hesitating between two designs of a database project using Hibernate. Design #1. (1) Create a general data provider interface, including a set of DAO interfaces and general data container classes. It hides the underneath implementation. A data provider implementation could access data in database, or an XML file, or a service, or something else. The user of a data provider does not to know about it. (2) Create a database library with Hibernate. This library implements the data provider interface in (1). The bad thing about Design #1 is that in order to hide the implementation details, I need to create two sets of data container classes. One in the general data provider interface - let's call them DPI-Objects, the other set is used in the database library, exclusively for entity/attribute mapping in Hibernate - let's call them H-Objects. In the DAO implementation, I need to read data from database to create H-Objects (via Hibernate) and then convert H-Objects into DPI-Objects. Design #2. Do not create a general data provider interface. Expose H-Objects directly to components that use the database lib. So the user of the database library needs to be aware of Hibernate. I like design #1 more, but I don't want to create two sets of data container classes. Is that the right way to hide H-Objects and other Hibernate implementation details from the user who uses the database-based data provider? Are there any drawbacks of Design #2? I will not implement other data provider in the new future, so should I just forget about the data provider interface and use Design #2? What do you think about this? Thanks for your time!

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  • Grabbing random object from ArrayList is not random.

    - by Isai
    I am creating a method where if you pass in a parameter of type Random, then it will return a random object. Here is basically what I am trying to do: public T choose(Random r) { int randomInt = r.nextInt(randomList.size()); // randomList is just a instance variable return randomList.get(randomInt); } The random list has this the following strings:[2, 2, 2, 1, 1, 1, 1, c, c, c, a, a, a, a] Then I made a driver with the following code for (int i = 0; i < 10; i++) { System.out.print(rndList.choose(rnd)); // rnd is initialized as a static Random variable } However my outputs are not coming out random. I used the debugger and found out that my choose method generates an integer that is relatively low, so it will always print out either 2's or 1's but never c's or a's. I can't figure out why this is happening and help would be greatly appreciated.

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  • Merging columns in a JTable

    - by Harish
    I am working in JTable and I have a requirement like this. Say There are 4 columns namely 10,20,30,40 Now the value usually comes like 10-20 20-30 and 30-40 So it was easy for us to display the name for this range. But recently the values have started to come randomly like 15-25 10-25,25-30 In this case our JTable should dynamically adjust the size of the row such that it represents that range only meaning it should not disturb the existing cells and only rows which diverge from the normal range. TO be more precise I should be able to merge and split cells based on the content of the cell.

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