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  • java thread - run() and start() methods

    - by JavaUser
    Please explain the output of the below code: If I call th1.run() ,the output is EXTENDS RUN RUNNABLE RUN If I call th1.start() , the output is : RUNNABLE RUN EXTENDS RUN Why this inconsistency . Please explain. class ThreadExample extends Thread{ public void run(){ System.out.println("EXTENDS RUN"); } } class ThreadExampleRunnable implements Runnable { public void run(){ System.out.println("RUNNABLE RUN "); } } class ThreadExampleMain{ public static void main(String[] args){ ThreadExample th1 = new ThreadExample(); //th1.start(); th1.run(); ThreadExampleRunnable th2 = new ThreadExampleRunnable(); th2.run(); } }

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  • Java: using generic wildcards with subclassing

    - by gibberish
    Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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  • Embeddable database better than SQLite for java

    - by dexter
    I am creating a web application that is accessing a SQLite database in the server. I also have "clients" that updates this same database. As we know SQLite locks the entire database during INSERTs which are done by the clients and the web application is also trying to make some UPDATEs at the same time. So my problem now is about concurrency in database access. I would like to use an embeddable database like SQLite. Any suggestions.

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  • java regular expression

    - by BSingh
    I am trying to write a regular expression for somethin like s1 = I am at Boston at Dowtown s2 = I am at Miami I am interested in the words after at eg: Boston, Downtown, Miami I have not been successful in creating a regex for that. Somethin like > .*? (at \w+)+.* gives just Boston in s1 (Downtown is missed). it just matches the first "at" Any suggestions

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  • Communication via internet in Java

    - by Stuart
    What I mean is like servers on video games. You can run an application and it will set up a server on your computer with an IP and a port. For example, how would you make an application where one host application sets up a thing where it has an IP and a port, and another computer that has access to the internet as well can type in the IP and port and it would be able to communicate with the host? I mean simple communication, like sending a boolean or String. And would there be any security problems that would be needed to fix?

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  • Java: how to read BufferedReader faster

    - by Cata
    Hello, I want to optimize this code: InputStream is = rp.getEntity().getContent(); BufferedReader reader = new BufferedReader(new InputStreamReader(is)); String text = ""; String aux = ""; while ((aux = reader.readLine()) != null) { text += aux; } The thing is that i don't know how to read the content of the bufferedreader and copy it in a String faster than what I have above. I need to spend as little time as possible. Thank you

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • Java: when to use static methods

    - by KP65
    Hello, I am wondering when to use static methods? Say If i have a class with a few getters and setters, a method or two, and i want those methods only to be invokable on an instance object of the class. Does this mean i should use a static method? e.g Obj x = new Obj(); x.someMethod or Obj.someMethod (is this the static way?) I'm rather confused!

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  • Java: JPQL search -similar- strings

    - by bguiz
    What methods are there to get JPQL to match similar strings? By similar I mean: Contains: search string is found within the string of the matches entity Case-insensitive Small mispellings: e.g. "arow" matches "arrow" I suspect the first two will be easy, however, I would appreciate help with the last one Thank you

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  • How to delete duplicate/aggregate rows faster in a file using Java (no DB)

    - by S. Singh
    I have a 2GB big text file, it has 5 columns delimited by tab. A row will be called duplicate only if 4 out of 5 columns matches. Right now, I am doing dduping by first loading each coloumn in separate List , then iterating through lists, deleting the duplicate rows as it encountered and aggregating. The problem: it is taking more than 20 hours to process one file. I have 25 such files to process. Can anyone please share their experience, how they would go about doing such dduping? This dduping will be a throw away code. So, I was looking for some quick/dirty solution, to get job done as soon as possible. Here is my pseudo code (roughly) Iterate over the rows i=current_row_no. Iterate over the row no. i+1 to last_row if(col1 matches //find duplicate && col2 matches && col3 matches && col4 matches) { col5List.set(i,get col5); //aggregate } Duplicate example A and B will be duplicate A=(1,1,1,1,1), B=(1,1,1,1,2), C=(2,1,1,1,1) and output would be A=(1,1,1,1,1+2) C=(2,1,1,1,1) [notice that B has been kicked out]

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  • Load/Store Objects in file in Java

    - by brain_damage
    I want to store an object from my class in file, and after that to be able to load the object from this file. But somewhere I am making a mistake(s) and cannot figure out where. May I receive some help? public class GameManagerSystem implements GameManager, Serializable { private static final long serialVersionUID = -5966618586666474164L; HashMap<Game, GameStatus> games; HashMap<Ticket, ArrayList<Object>> baggage; HashSet<Ticket> bookedTickets; Place place; public GameManagerSystem(Place place) { super(); this.games = new HashMap<Game, GameStatus>(); this.baggage = new HashMap<Ticket, ArrayList<Object>>(); this.bookedTickets = new HashSet<Ticket>(); this.place = place; } public static GameManager createManagerSystem(Game at) { return new GameManagerSystem(at); } public boolean store(File f) { try { FileOutputStream fos = new FileOutputStream(f); ObjectOutputStream oos = new ObjectOutputStream(fos); oos.writeObject(games); oos.writeObject(bookedTickets); oos.writeObject(baggage); oos.close(); fos.close(); } catch (IOException ex) { return false; } return true; } public boolean load(File f) { try { FileInputStream fis = new FileInputStream(f); ObjectInputStream ois = new ObjectInputStream(fis); this.games = (HashMap<Game,GameStatus>)ois.readObject(); this.bookedTickets = (HashSet<Ticket>)ois.readObject(); this.baggage = (HashMap<Ticket,ArrayList<Object>>)ois.readObject(); ois.close(); fis.close(); } catch (IOException e) { return false; } catch (ClassNotFoundException e) { return false; } return true; } . . . } public class JUnitDemo { GameManager manager; @Before public void setUp() { manager = GameManagerSystem.createManagerSystem(Place.ENG); } @Test public void testStore() { Game g = new Game(new Date(), Teams.LIONS, Teams.SHARKS); manager.registerGame(g); File file = new File("file.ser"); assertTrue(airport.store(file)); } }

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  • How to rotate an image properly in JPanel (Java)

    - by Bruce
    Hi guys, I'm working on rotating a loaded image. I set the graphics on a JPanel and then use standard AffineTransform in order to rotate it, say, 45 degrees. Unfortunately, the image is being cut, if it exceeds the panel area. How may I force JPanel to add scrolls to itself (while loading an image file, I would like to adjust the size of JPanel by adding the scrolls, without adjusting the size of JFrame). Or, in other words, how to correctly rotate the whole image? Thank you in advance for the reply!

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  • Java JPA @OneToMany neededs to reciprocate @ManyToOne?

    - by bguiz
    Create Table A ( ID varchar(8), Primary Key(ID) ); Create Table B ( ID varchar(8), A_ID varchar(8), Primary Key(ID), Foreign Key(A_ID) References A(ID) ); Given that I have created two tables using the SQL statements above, and I want to create Entity classes for them, for the class B, I have these member attributes: @Id @Column(name = "ID", nullable = false, length = 8) private String id; @JoinColumn(name = "A_ID", referencedColumnName = "ID", nullable = false) @ManyToOne(optional = false) private A AId; In class A, do I need to reciprocate the many-to-one relationship? @Id @Column(name = "ID", nullable = false, length = 8) private String id; @OneToMany(cascade = CascadeType.ALL, mappedBy = "AId") private List<B> BList; //<-- Is this attribute necessary? Is it a necessary or a good idea to have a reciprocal @OneToMany for the @ManyToOne? If I make the design decision to leave out the @OneToMany annotated attribute now, will come back to bite me further down.

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  • Java/Swing: Problem with key listener

    - by Mike
    I have a search dialog with a JTextField that's being used as a search box. When the user types something, it searches the DB, shows the result in a JTable and selects the first item in it. If the first result is what they were looking for, I want to let them quickly accept the dialog, by pressing Enter (while the JTextField is focused). So I added a KeyListener to the JTextField and it's working OK. Now the problem: The user opens can open the dialog by pressing Enter when a "Search" button on the dialog's parent frame is focused. The dialog is displayed and the JTextField gets the keyReleased event (from the Enter key that displayed it), so it shows up and closes. If the user holds Enter down, then the JTextField receives the keyPressed, keyTyped and keyReleased events. How can I fix without resorting to ugly workarounds? Platform is Windows 7 x64, btw. Test NetBeans project here: http://dl.dropbox.com/u/6354360/KeyListenerTest.zip Thanks.

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  • Java data structure suggestion.

    - by techoverflow
    Hi folks, I am a newbie in this field so please excuse my silly mistakes :) So the issue I am facing is: On my webpage, I am displaying a table. For now my issue is concerned with three columns of the table. First is : Area Code Second is : Zone Code Third is: Value The relationship between these three is: 1 Area Code has 6 different Zone code's and all those 6 Zone codes have corresponding "Value" I need a data structer that would give me the flexibility to get a "Value" for a Zone code, which falls under a particular Area code. I have the same zone codes for all the Area codes: Zone codes are: 111, 222, 333, 444, 555, 666 After surfing your stackoverflow, I thought I can go with this structure: Map<Integer, Map<Integer, Double>> retailPrices = new HashMap<Integer, Map<Integer, Double>>(); Map<Integer, Double> codes = new HashMap<Integer, Double>(); where reatailPrices would hold an Area Code and a Map of Zone code as Key and "Value" as Value. but when I am trying to populate this through a SQL resultset, I am getting the following error: The method put(Integer, Map<Integer,Double>) in the type Map is not applicable for the arguments (Integer, Double) on line: `while(oResult.next()) retailPrices.put((new Integer(oResult.getString("AREA"))), (pegPlPrices.put(new Integer(oResult.getString("ZONE_CODE")), new Double(oResult.getString("VALUE"))))); }` please help me figure out this problem. Am I following the right approach?

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  • non blocking client server chat application in java using nio

    - by Amith
    I built a simple chat application using nio channels. I am very much new to networking as well as threads. This application is for communicating with server (Server / Client chat application). My problem is that multiple clients are not supported by the server. How do I solve this problem? What's the bug in my code? public class Clientcore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void coreClient() { System.out.println("please enter the text"); BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in)); SocketChannel sc = null; try { sc = SocketChannel.open(); sc.configureBlocking(false); sc.connect(new InetSocketAddress(8888)); int i=0; while (!sc.finishConnect()) { } for(int ii=0;ii>-22;ii++) { System.out.println("Enter the text"); String HELLO_REQUEST =stdin.readLine().toString(); if(HELLO_REQUEST.equalsIgnoreCase("end")) { break; } System.out.println("Sending a request to HelloServer"); ByteBuffer buffer = ByteBuffer.wrap(HELLO_REQUEST.getBytes()); sc.write(buffer); } } catch (IOException e) { e.printStackTrace(); } finally { if (sc != null) { try { sc.close(); } catch (Exception e) { e.printStackTrace(); } } } } public void run() { try { coreClient(); } catch(Exception ej) { ej.printStackTrace(); }}} public class ServerCore extends Thread { SelectionKey selkey=null; Selector sckt_manager=null; public void run() { try { coreServer(); } catch(Exception ej) { ej.printStackTrace(); } } private void coreServer() { try { ServerSocketChannel ssc = ServerSocketChannel.open(); try { ssc.socket().bind(new InetSocketAddress(8888)); while (true) { sckt_manager=SelectorProvider.provider().openSelector(); ssc.configureBlocking(false); SocketChannel sc = ssc.accept(); register_server(ssc,SelectionKey.OP_ACCEPT); if (sc == null) { } else { System.out.println("Received an incoming connection from " + sc.socket().getRemoteSocketAddress()); printRequest(sc); System.err.println("testing 1"); String HELLO_REPLY = "Sample Display"; ByteBuffer buffer = ByteBuffer.wrap(HELLO_REPLY.getBytes()); System.err.println("testing 2"); sc.write(buffer); System.err.println("testing 3"); sc.close(); }}} catch (IOException e) { e.printStackTrace(); } finally { if (ssc != null) { try { ssc.close(); } catch (IOException e) { e.printStackTrace(); } } } } catch(Exception E) { System.out.println("Ex in servCORE "+E); } } private static void printRequest(SocketChannel sc) throws IOException { ReadableByteChannel rbc = Channels.newChannel(sc.socket().getInputStream()); WritableByteChannel wbc = Channels.newChannel(System.out); ByteBuffer b = ByteBuffer.allocate(1024); // read 1024 bytes while (rbc.read(b) != -1) { b.flip(); while (b.hasRemaining()) { wbc.write(b); System.out.println(); } b.clear(); } } public void register_server(ServerSocketChannel ssc,int selectionkey_ops)throws Exception { ssc.register(sckt_manager,selectionkey_ops); }} public class HelloClient { public void coreClientChat() { Clientcore t=new Clientcore(); new Thread(t).start(); } public static void main(String[] args)throws Exception { HelloClient cl= new HelloClient(); cl.coreClientChat(); }} public class HelloServer { public void coreServerChat() { ServerCore t=new ServerCore(); new Thread(t).start(); } public static void main(String[] args) { HelloServer st= new HelloServer(); st.coreServerChat(); }}

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  • Profiling a Java Spring application

    - by niklassaers
    Hi guys, I have a Spring application that I believe has some bottlenecks, so I'd like to run it with a profiler to measure what functions take how much time. Any recommendations to how I should do that? I'm running STS, the project is a maven project, and I'm running Spring 3.0.1 Cheers Nik

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  • How to login to gdata in GWT application deployed on GAE?

    - by Raffo
    I want to use the Google account login to retrieve the informations to be used for Google's gdata api so that when I start the application deployed on Google App Engine the user is asked for its login and I can then use this information on the server side to specify the credentials for Google Calendar login (through gdata api). How can I do that? I tried using Client login but it seems that there's no way to get password information from che Client object on the server side... thank you.

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  • Building "isolated" and "automatically updated" caches (java.util.List) in Java.

    - by Aidos
    Hi Guys, I am trying to write a framework which contains a lot of short-lived caches created from a long-living cache. These short-lived caches need to be able to return their entier contents, which is a clone from the original long-living cache. Effectively what I am trying to build is a level of transaction isolation for the short-lived caches. The user should be able to modify the contents of the short-lived cache, but changes to the long-living cache should not be propogated through (there is also a case where the changes should be pushed through, depending on the Cache type). I will do my best to try and explain: master-cache contains: [A,B,C,D,E,F] temporary-cache created with state [A,B,C,D,E,F] 1) temporary-cache adds item G: [A,B,C,D,E,F] 2) temporary-cache removes item B: [A,C,D,E,F] master-cache contains: [A,B,C,D,E,F] 3) master-cache adds items [X,Y,Z]: [A,B,C,D,E,F,X,Y,Z] temporary-cache contains: [A,C,D,E,F] Things get even harder when the values in the items can change and shouldn't always be updated (so I can't even share the underlying object instances, I need to use clones). I have implemented the simple approach of just creating a new instance of the List using the standard Collection constructor on ArrayList, however when you get out to about 200,000 items the system just runs out of memory. I know the value of 200,000 is excessive to iterate, but I am trying to stress my code a bit. I had thought that it might be able to somehow "proxy" the list, so the temporary-cache uses the master-cache, and stores all of it's changes (effectively a Memento for the change), however that quickly becomes a nightmare when you want to iterate the temporary-cache, or retrieve an item at a specific index. Also given that I want some modifications to the contents of the list to come through (depending on the type of the temporary-cache, whether it is "auto-update" or not) and I get completly out of my depth. Any pointers to techniques or data-structures or just general concepts to try and research will be greatly appreciated. Cheers, Aidos

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  • Social Media Java Design Problem

    - by jboyd
    I need to put something together quickly that will take blog posts and place them on social media sites, the requirements are as follows: Blog Entries are independent records that already exist, they have a published date and a modified date, the blog entry application cannot be changed, at least not substantially A new blog entry, or update needs to be sent to social media sites I currently do not need to update or delete social media communications if the blog entry is edited, or deleted, though I may need to later My design problems here are as follows: how do I know the status of each update how can I figure out what blog entry updates and postings have already been sent out? how can I quickly poll the blog entry table for postings that haven't yet been sent out? Avoiding looking at each Entry record from the DB as an object and asking if it's been sent already. That would be too slow. I cannot hook into any Blog Entry update code, my only option would be to create a trigger that an update queues something to be processed I'm looking for general guiding principles here, the biggest problem I'm having is coming up with any reasonable way to figure out if a blog entry should be sent to our social media sites in the first place

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  • Garbage Collection Java

    - by simion
    On the slides i am revising from it says the following; Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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