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  • Synchronizing access to an inner object's methods?

    - by user291701
    Suppose I have the following: public class Foo { private ReadingList mReadingList = new ReadingList(); public ReadingList getReadingList() { synchronized (mReadingList) { return mReadingList; } } } If I try modifying the ReadingList object in two threads, the synchronization above won't help me, right?: // Thread 1 foo1.getReadingList().setName("aaa"); // Thread 2 foo2.getReadingList().setName("bbb"); do I have to wrap each method I want synchronized like so: public class Foo { private ReadingList mReadingList = new ReadingList(); public synchronized void setReadingListName(String name) { mReadingList.setName(name); } public synchronized void setReadingListAuthor(String author) { mReadingList.setAuthor(author); } ... and so on for each method of ReadingList I want exposed and synched? I'd end up just writing wrapper methods for each method of ReadingList. Thanks

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  • J2EE/EJB + service locator: is it safe to cache EJB Home lookup result ?

    - by Guillaume
    In a J2EE application, we are using EJB2 in weblogic. To avoid losing time building the initial context and looking up EJB Home interface, I'm considering the Service Locator Pattern. But after a few search on the web I found that event if this pattern is often recommended for the InitialContext caching, there are some negative opinion about the EJB Home caching. Questions: Is it safe to cache EJB Home lookup result ? What will happen if one my cluster node is no more working ? What will happen if I install a new version of the EJB without refreshing the service locator's cache ?

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  • Conceptual inheritance implementation

    - by TheSENDER
    Hi there, I'm writing a spatial data structure and I have a doubt about what's the best NODE implementation. According to my design I have an abstract node entity and three classes which inherit from it: EMPTYNODE, FULLNODE, INTERNALNODE. The first one has no particular data. The second one has 1 reference to a generic element. The third one has 2 references to other nodes. I have found several ways to implement this situation (that I have already coded) but I can't decide what's the best. The first solution that I have found is to use a single class Node that potentially performs all the operation in this way: private static class Node { private Elem elem = null; private Node left = null, right = null; public Elem getElem() { assert isFull(); return elem; } public boolean isEmpty() { return elem == null && left == null; } public boolean isFull() { return elem != null; } public boolean isInternal() { return elem == null && left != null; } } The second solution is to write an explicit division by classes where every class offers only its methods. Obviously in this way we are obliged to perform several casts to the node objects. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); } private static class FullNode extends Node{ private ITriangle elem; @Override public boolean isEmpty() { return false; } @Override public final boolean isFull() { return true; } @Override public final boolean isInternal() { return false; } public Elem getElem() { return elem; } } The third one solution is to use the inheritance allowing every classes to offer all the methods, but the object type should by check by "isEmpty()" and similar methods. In case of wrong call we'll throw an exception. private static abstract class Node { public abstract boolean isEmpty(); public abstract boolean isFull(); public abstract boolean isInternal(); public abstract Elem getElem(); } private static class Empty extends Node{ @Override public boolean isEmpty() { return true; } @Override public final boolean isFull() { return false; } @Override public final boolean isInternal() { return false; } @Override public Elem getElem() { throw new AssertionError(); } } What do you think about these three solutions? Which one would you use? Any other ideas? Thanks for your help. Every idea will be appreciated.

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  • Is there a design pattern to cut down on code duplication when subclassing Activities in Android?

    - by Daniel Lew
    I've got a common task that I do with some Activities - downloading data then displaying it. I've got the downloading part down pat; it is, of course, a little tricky due to the possibility of the user changing the orientation or cancelling the Activity before the download is complete, but the code is there. There is enough code handling these cases such that I don't want to have to copy/paste it to each Activity I have, so I thought to create an abstract subclass Activity itself such that it handles a single background download which then launches a method which fills the page with data. This all works. The issue is that, due to single inheritance, I am forced to recreate the exact same class for any other type of Activity - for example, I use Activity, ListActivity and MapActivity. To use the same technique for all three requires three duplicate classes, except each extends a different Activity. Is there a design pattern that can cut down on the code duplication? As it stands, I have saved much duplication already, but it pains me to see the exact same code in three classes just so that they each subclass a different type of Activity.

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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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  • Strange befaviour of spring transaction support for JPA + Hibernate +@Transactional annotation

    - by abovesun
    I found out really strange behavior on relatively simple use case, probably I can't understand it because of not deep knowledges of spring @Transactional nature, but this is quite interesting. I have simple User dao that extends spring JpaDaoSupport class and contains standard save method: @Transactional public User save(User user) { getJpaTemplate().persist(user); return user; } If was working fine until I've add new method to same class: User getSuperUser(), this method should return user with isAdmin == true, and if there is no super user in db, method should create one. Thats how it was looking like: public User createSuperUser() { User admin = null; try { admin = (User) getJpaTemplate().execute(new JpaCallback() { public Object doInJpa(EntityManager em) throws PersistenceException { return em.createQuery("select u from UserImpl u where u.admin = true").getSingleResult(); } }); } catch (EmptyResultDataAccessException ex) { User admin = new User('login', 'password'); admin.setAdmin(true); save(admin); // THIS IS THE POINT WHERE STRANGE THING COMING OUT } return admin; } As you see code is strange forward and I was very confused when found out that no transaction was created and committed on invocation of save(admin) method and no new user wasn't actually created despite @Transactional annotation. In result we have situation: when save() method invokes from outside of UserDAO class - @Transactional annotation counted and user successfully created, but if save() invokes from inside of other method of the same dao class - @Transactional annotation ignored. Here how I was change save() method to force it always create transaction. public User save(User user) { getJpaTemplate().execute(new JpaCallback() { public Object doInJpa(EntityManager em) throws PersistenceException { em.getTransaction().begin(); em.persist(user); em.getTransaction().commit(); return null; } }); return user; } As you see I manually invoke begin and commit. Any ideas?

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  • Semantics of repeated acknowledgments in JMS

    - by Lajos Nagy
    Suppose I decide to call acknowledgment() on a JMS message several times. Say the first call fails (for non-permanent reason). Does the success of the second (or any subsequent) call guarantee that the message is now acknowledged? Is the exact behavior of acknowledgement() specified anywhere?

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  • ant conditions problem

    - by senzacionale
    I have problem with ant. I woul dlike to use conditions in ant. But i get error of: BUILD FAILED C:\Projekti\Projekt ANT\build.xml:412: Problem: failed to create task or type Cause: The name is undefined. Action: Check the spelling. Action: Check that any custom tasks/types have been declared. Action: Check that any / declarations have taken place. and this is code: <target name="test"> <input message="Write some text: " addproperty="foo" /> <if> <equals arg1="${foo}" arg2="bar" /> <then> <echo message="The value of property foo is 'bar'" /> </then> <elseif> <equals arg1="${foo}" arg2="foo" /> <then> <echo message="The value of property foo is 'foo'" /> </then> </elseif> <else> <echo message="The value of property foo is not 'foo' or 'bar'" /> </else> </if> </target>

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  • How to organize RMI Client-Server eBanking architecture

    - by xenom
    I am developing a secured eBanking service in RMI with a GUI both for Server and Client. The Server must be able to log every operations (new User, deleted User, Withdrawal, Lodgement...) The Client will do these operations. As everything is secured, the Client must at first, create an account with a name and a password in the GUI. After that, the GUI adds the User in the Bank UserList(arrayList) as a new Customer and the User can do several operations. It seems straightforward at first but I think my conception is not correct. Is it correct to send the whole Bank by RMI ? Because at first I thought Bank would be the server but I cannot find another way to do that. Currently, the Client GUI asks for a login and a password, and receives the Bank by RMI. A User is characterized by a name and a hash of the password. private String name; private byte[] passwordDigest; In fact the GUI is doing every security checking and I don't know if it's relevant. When you type login//password, it will search the login in the Bank and compare the hash of the password. In fact I have the impression that the Client knows too much information because when you have the Bank you have everything.. Does it seem correct or do I need to change my implementation ?

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  • Android - Memory leak when dynamically building UI with image resource backgrounds

    - by Rich
    I have an Activity that I swear is leaking memory. The app I'm working on does a lot with images, so I've had to be pretty stingy with memory when working directly with Bitmaps. I added an Activity, and now if you use this new Activity it basically puts me over the edge with mem usage and I end up throwing the "Bitmap exceeds VM budget" exception. If you never launch this Activity, everything is smooth as it was previously. I started reading about memory leaks, and I think that I have a similar situation to what is described in the article in the Android docs. I'm dynamically creating a bunch of image views and adding a BackgroundDrawable from the resources and adding an OnClickListener as well. I imagine I have to do some cleanup when the Activity hits onPause in its life cycle, but I'd like to know specifically what is the correct way. Here is the code that should demonstrate the objects I'm working with... LinearLayout templateContainer; . . . ImageView imgTemplatePreview = (ImageView) item.findViewById(R.id.imgTemplatePreview); . . . imgTemplatePreview.setBackgroundDrawable(getResources().getDrawable(previewId)); imgTemplatePreview.setOnClickListener(imgClick); templateContainer.addView(item);

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  • Is there a better way than a sequence of if's to handle events?

    - by Matt
    I recently ran across several objects implemented to handle events with a hard coded mapping using this pattern: public void handleEvent(Event event) { if(event.getCode() == SOME_STATIC_EVENT) doSomething(event); if(event.getCode() == ANOTHER_STATIC_EVENT) doSomethingElse(event); } where doSomething functions are implemented as methods of the same class. In hopes of striving for looser coupling, how would you suggest abstracting out this pattern? Also, what's the best approach for mapping 0..N functions to a fired event?

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  • How should I link two items with MouseMovementListeners?

    - by user1708810
    I'm working on a program that will display two "views" of the same set of items. So I need to have something set up so that when the top down view is changed, the side view is updated (and vice versa). Here's a brief outline of the relevant code so you can get an idea of my structure so far: public class DraggableComponent extends JComponent { //Contains code for MouseMovementListener that makes the item draggable } public class ItemGraphic extends DraggableComponent { //Code to render the graphic } public class Item { private ItemGraphic topGraphic; private ItemGraphic sideGraphic; } I'm able to get each graphic to display fine in my GUI. I can also independently drag each graphic. I'm missing the "linking." Some ideas I've been thinking about: Have one listener for the whole GUI. Loop through each Item and if the cursor is within the bounds of either graphic, move the other graphic. I'm concerned about the efficiency of this method. Multiple "paired" listeners (not quite sure how this would work, but the idea is that each graphic would have a listener for the other paired graphic)

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  • Text to speech(TTS)-Android

    - by bharathi
    Hi, I am new to this android platform.now I am Working on TTS(Text to Speech).what I am trying to do is that when i enter the text in the Text area it has to be converted to speech,when i click the speak button.can anyone help me out.Thanks in Advance.

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  • JMS Acknowledge Asynchronous Message

    - by x1a0
    Hi, How do I acknowledge a message when I am using a message listener? I get the following error when I try to do an acknowledge in my message listener. A synchronous method call is not permitted when a session is being used asynchronously: 'acknowledge'

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  • Given an array of integers [x0 x1 x2], how do you calculate all possible permutations from [0 0 0] t

    - by user319951
    I am writing a program that takes in an ArrayList and I need to calculate all possible permutations starting with a list of zeroes, up to the value in the corresponding input list. Does anyone know how to iteratively calculate these values? For example, given [ 1 2 ] as input, it should find and store the following lists: [0 0], [1 0], [1 1], [1 2], [0 1], [0 2] Thanks!

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  • How do I pass an ArrayList to method that takes a collection as an input

    - by Ankur
    I want to pass some ArrayList X into method a(Collection someCol) that takes Collection as an input. How can I do this? I thought an ArrayList was a Collection and thus I should be able to "just do it" but it seems that Collection is an interface and ArrayList implements this interface. Is there something I can do to make this work ... if you understand the theory that would also help me and possibly lots of other people. Thanks

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  • One account, multiple users, multiple shopping cart in a web application

    - by lemotdit
    I received a somewhat unusual request (imo) for a transactional web site. I have to implement the possibility of having multiple shopping cart for the same user. Those really are shopping carts, not order templates. I.E: A store with several departments ordering under the same account, but with a different person placing orders for a specific department only. Having more than one user per account is not an option since it would involve 'too much' management from the stores owner and the admins. Anyone had to deal with this before? The option so far is to have names for shopping cart, and a dropdown list or something alike after login to choose the cart with some kind of 'busy flag' to lock the cart if it's in use in another session.

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  • XML Doc to JSP to TIFF

    - by SPD
    We have around 100 word templates, every time user gets a business request he goes into shared folder select the template he/she wants and enter information and save it as tiff, these tiffs later processed by some batch program. I am trying to automate this process. So I defined an XML which has Template information like <Template id="1"> <Section id="1"> <fieldName id="1">Date</fieldName> <fieldValue></fieldValue> <fieldtype></fieldType> <fieldProperty>textField</fieldProperty> </Section> <Section id="2"> <fieldName id="2">Claim#</fieldName> <fieldValue></fieldValue> <fieldtype></fieldType> <fieldProperty>textField</fieldProperty> </Section> </Template> Based on the template values I generate the JSP on fly. Now I would like to generate a TIFF file out of it in specified format. I am not sure how to handle this requirement. *edited the original question.

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  • J2SE Client Server App: Client calls RMI method. Server handles RMI method and returns, but Client

    - by Mike
    J2SE Client Server App: Client calls RMI message. Server handles RMI method and returns, but Client never receives it. Any ideas how this could happen? Our attempted solution is to set client read timeouts and come up with a framework for resending requests or otherwise handling those failures gracefully. But really, I'd like to know any root causes for how this might happen rather than addressing the symptoms.

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  • Creating android app Database with big amount of data

    - by Thomas
    Hi all, The database of my application need to be filled with a lot of data, so during onCreate(), it's not only some create table sql instructions, there is a lot of inserts. The solution I chose is to store all this instructions in a sql file located in res/raw and which is loaded with Resources.openRawResource(id). It works well but I face to encoding issue, I have some accentuated caharacters in the sql file which appears bad in my application. This my code to do this : public String getFileContent(Resources resources, int rawId) throws IOException { InputStream is = resources.openRawResource(rawId); int size = is.available(); // Read the entire asset into a local byte buffer. byte[] buffer = new byte[size]; is.read(buffer); is.close(); // Convert the buffer into a string. return new String(buffer); } public void onCreate(SQLiteDatabase db) { try { // get file content String sqlCode = getFileContent(mCtx.getResources(), R.raw.db_create); // execute code for (String sqlStatements : sqlCode.split(";")) { db.execSQL(sqlStatements); } Log.v("Creating database done."); } catch (IOException e) { // Should never happen! Log.e("Error reading sql file " + e.getMessage(), e); throw new RuntimeException(e); } catch (SQLException e) { Log.e("Error executing sql code " + e.getMessage(), e); throw new RuntimeException(e); } The solution I found to avoid this is to load the sql instructions from a huge static final string instead of a file, and all accentutated characters appears well. But Isn't there a more elegant way to load sql instructions than a big static final String attribute with all sql instructions ? Thanks in advance Thomas

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