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  • Generics List Interface...newb question

    - by newToProgramming
    The List interface is the following: public interface List<E>{ public boolean add(Object e); public boolean remove(Object e); public boolean contains(Object e); ...etc Why aren't the add, remove and contains methods written like the following? public boolean add(E e) public boolean remove(E e) public boolean contains(E e)

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  • How did this get 8?

    - by David
    Here's the code: class qual { public static int fibonacci(int n) { if (n == 0 || n == 1) { return 1; } else { return fibonacci(n-1) + fibonacci(n-2); } } public static void main(String[] arg) { System.out.println(fibonacci(5)); } } The output was 8. The output should be 8 but when I look at this I think it should be 7 ((5-1) +(5-2)). Why was the output 8? I think the reasoning behind getting 8 will make recursion maybe stop being confusing for me.

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  • How to display a confirmation message in Tapestry5?

    - by shane87
    I am developing a website as part of my final year project and I want to display a message which confirms that an email has been sent. I know how to display custom error messages on a form i.e. You cannot go any further until the following errors are fixed : login name not known! I want to display a message which will say: your email has been sent! after I send an email. I have been told that I should display this message through the flash. I am unsure on how to do this, any help would be greatly appreciated.

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  • Fast response on first Socket I/O request but slow every other time when communicating with remote serial port

    - by GreenGodot
    I'm using sockets to pass Serial commands to a remote device. And the response to that request is sent back and printed out. However, I am having a problem in that the first time it is instant but the rest of the time it can take up to 20 seconds to receive a reply. I think the problem is with my attempt at threading but I am not entirely sure. new Thread() { @Override public void run() { System.out.println("opened"); try { isSocketRetrieving.setText("Opening Socket"); socket = new Socket(getAddress(), getRemotePort())); DataOutput = new DataOutputStream(socket .getOutputStream()); inFromServer = new BufferedReader( new InputStreamReader(socket .getInputStream())); String line = ""; isSocketRetrieving.setText("Reading Stream......"); while ((line = inFromServer.readLine()) != null) { System.out.println(line); if (line.contains(getHandshakeRequest())) { DataOutput.write((getHandshakeResponse()toString() + "\r").getBytes()); DataOutput.flush(); DataOutput .write((getCommand().toString() + "\r").getBytes()); DataOutput.flush(); int pause = (line.length()*8*1000)/getBaud(); sleep(pause); } else if (line.contains(readingObject .getExpected())) { System.out.println(line); textArea.append("value = " + line + "\n"); textAreaScroll.revalidate(); System.out.println("Got Value"); break; } } System.out.println("Ended"); try { inFromServer.close(); DataOutput.close(); socket.close(); isSocketRetrieving.setText("Socket is inactive..."); rs232Table.addMouseListener(listener); interrupt(); join(); } catch (IOException e) { e.printStackTrace(); } catch (InterruptedException e) { System.out.println("Thread exited"); } } catch (NumberFormatException e1) { e1.printStackTrace(); } catch (UnknownHostException e1) { e1.printStackTrace(); } catch (IOException e1) { e1.printStackTrace(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }.start();

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  • Howto check if a object is connected to another in hibernate

    - by codevourer
    Imagine two domain object classes, A and B. A has a bidirectional one-to-many relationship to B. A is related to thousands of B. The relations must be unique, it's not possible to have a duplicate. To check if an instance of B is already connected to a given instance of A, we could perform an easy INNER JOIN but this will only ensure the already persisted relations. What about the current transient relations? class A { @OneToMany private List<B> listOfB; } If we access the listOfB and perform a check of contains() this will fetch all the connected instances of B lazy from the datasource. I only want to validate them by their primary-key. Is there an easy solution where I can do things like "Does this instance of A is connected with this instance of B?" Without loading all these data into memory and perform a based on collections?

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  • How do "modern JVMs" differ from older JVMs?

    - by Lord Torgamus
    Here's a phrase that I heard a lot throughout high school and university computer science classes: "That's not an issue for modern JVMs." Usually this would come up in discussions about overall performance or optimization strategies. It was always treated as a kind of magical final answer, though, as if it makes issues no longer worth thinking about. And that just leads me to wonder: what are the differences between the prototypical "modern JVM" and older JVMs, really?

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  • How to design authentication in a thick client, to be fail safe?

    - by Jay
    Here's a use case: I have a desktop application (built using Eclipse RCP) which on start, pops open a dialog box with 'UserName' and 'Password' fields in it. Once the end user, inputs his UserName and Password, a server is contacted (a spring remote-servlet, with the client side being a spring httpclient: similar to the approaches here.), and authentication is performed on the server side. A few questions related to the above mentioned scenario: If said this authentication service were to go down, what would be the best way to handle further proceedings? Authentication is something that I cannot do away with. Would running the desktop client in a "limited" mode be a good idea? For instance, important features/menus/views will be disabled, rest of the application will be accessible? Should I have a back up authentication service running on a different machine, working as a backup? What are the general best-practices in this scenario? I remember reading about google gears and how it would let you edit and do stuff offline - should something like this be designed? Please let me know your design/architectural comments/suggestions. Appreciate your help.

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  • Playing craps, asking and printing

    - by Angelo Mejia
    How do I ask the amount of games of craps someone wants to play and print the number of wins as a result of n number of games? Also How do I make a table in the main method using the previous methods I have? A table like this but shows the results: Percent Wins Games Experiment Number 1 2 3 4 5 6 7 8 9 10 100 1000 10000 100000 1000000 public class CrapsAnalysis { public static int rollDie( int n) { return (int)(Math.random()*n) + 1 ; } public static int rollDice( ) { int die1 ; int die2 ; die1 = rollDie(6) ; die2 = rollDie(6) ; return die1 + die2 ; } public static boolean playOneGame( ) { int newDice ; //repeated dice rolls int roll ; //first roll of the dice int playerPoint = 0 ; //player point if no win or loss on first roll newDice = rollDice() ; roll = rollDice() ; if (roll == 7 || roll == 11) return true; else if (roll == 2 || roll == 3 || roll == 12) return false; else { playerPoint = roll; newDice = rollDice(); do { newDice = rollDice(); } while (newDice != playerPoint || newDice != 7) ; if (newDice == 7) return false; else return true; } } public static int playGames ( int n ) { int numWon = 0; for (int i = 1; i <= n; i++) if(playOneGame()) numWon++; return numWon; } public static void main(String[] args) { //Don't know how to ask and print out the results of the number of wins depending on the n number of games played } }

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  • Collections removeAll method

    - by srinannapa
    I would like to know if something like below is possible , list<**MyObject**>.**removeAll**(list<**String**>) I hope the context is understandable. The list<MyObject : is a ArrayList<MyObject The list<String : is a ArrayList<String I know this can be achieved by overriding equals method in MyObject class. I would like to know if any other choice is prsent. Thanks,Srinivas N

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  • How can I change the arrow style in a JComboBox

    - by Stephane Grenier
    Let's say I want to use a custom image for the arrow in JComboBox, how can I do this? I understand it's possible using the synth xml files, or maybe even UIManager.put(...), but I don't know how. All I want to do at this time is change the arrow image to something else, either programatically or even just overriding the image it uses. How exactly can I do this?

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  • Guice expert question

    - by Roman
    Hi All I am wondering if someone would be such an expert in guice that he even would know how to implement that : I have an injection annotation (@ConfParam)with some parameters , like that : class TestClass { private final int intValue; @Inject public TestClass(@ConfParam(section = "test1", key = "1") int intValue{ this.intValue = intValue; } public int getIntValue() { return intValue; } } The ConfParam is my custom annotation. Now , when the injection value is requested , I would like guice to create a dynamic binding, to resolve the value. For that binding I will need the parameters inside the annotation. Some example could be , I will have to look in the database in some table where the section is ? and the key is ?. All the trouble is that the data is not available when the injector is created and could be also be added at runtime. Ps. I static solution is easy. ( just have a look at the Names class)

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  • Better product to develop for, iPad or Android based tablet in a purely business related application

    - by Caylem
    Hey guys Just wondering what you'd suggest as the best platform for developing a business application for a tablet device. The application needs to be multitouch, have access to a maps API, a database on the device. It will not be going on sale in the app store or Androids market, it is purely for specific business task and not for the general consumer. Obviously the options seem to be iPhone OS and the iPad or Android and an Android tablet device. The form factor for the end product requires something in the region of 8 inch+ screen and enough processing power to provide a good experience for the end user. Any help would be much appreciated. Thanks

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  • Blackberry development

    - by user348369
    hi i am working as a blackberry development we require to make a chat messenger. i am face some problem. our messenger list is not update automatically and our offline message come same like a one message mean require sepration.

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  • Calling web service from seems to hang

    - by anothershrubery
    I am trying to call an asmx web service from an Android app. Just literally started some Android development today. I've been following various solutions I have found on the net and on here and it seems it is more difficult than anticipated. I have tried various solutions and using KSoap2 seems to be the easiest way to implement this, well it would be if I could get it working. I have the following code which works up until a point: private class CallWebService extends AsyncTask<Void, Void, Void> { private static final String SOAP_ACTION = "http://tempuri.org/GetUser"; private static final String METHOD_NAME = "GetUser"; private static final String NAMESPACE = "http://tempuri.org/"; private static final String URL = "http://160.10.1.79:59315/Service1.asmx"; TextView tv; @Override protected Void doInBackground(Void... params) { tv=(TextView)findViewById(R.id.txtMessage); try { SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME); SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11); envelope.dotNet=true; envelope.setOutputSoapObject(request); HttpTransportSE androidHttpTransport = new HttpTransportSE(URL); androidHttpTransport.call(SOAP_ACTION, envelope); Object result = (Object)envelope.getResponse(); tv.setText(result.toString()); } catch (Exception e) { tv.setText(e.getMessage()); } return null; } } It seems to hang at the line androidHttpTransport.call(SOAP_ACTION, envelope); Any ideas why? Is this the correct approach? Should I be looking in another direction?

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  • Unnecessary 'else' statement

    - by Vitalii Fedorenko
    As you know, in Eclipse you can turn on "Unnecessary 'else' statement" check that will trigger on if-then-else with premature return. And, from my experience, there are two most possible situations when use such statement: 1) Pre-check: if (validate(arg1)) { return false; } doLotOfStuff(); 2) Post-check: doLotOfStuff(); if (condition) { return foo; } else { return bar; } In the second case, if the trigger is on, Eclipse will suggest you to change the code to: doLotOfStuff(); if (condition) { return foo; } return bar; However, I think that the return with else statement is more readable as it is like direct mapping of business logic. So I am curios if this "Unnecessary 'else' statement" code convention is widespread or else statement is more preferable?

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  • Correct handling of return data

    - by Serhiy
    Hello, I have a question related to correct handling of returns of the DAO library I'm writing for one project. This library probably is going to be used by another people and I want to do it correctly. So I would like to know, how I should deal with return statements of the functions of my DAO. Example 1 I have function to getCustomer which should return String. In case query doesn't return any result should I return null, empty string or throw some kind of Exception? Example 2 I have function getCutomerList which return ArrayList. In case query doesn't return any result should I return null, empty ArrayList or throw some Exception? Example 3 Some sql exception was detected, what should I do: throw exception or do try..catch of the block where it can occur? What is the "good" practice or "best" practice to apply in my case? Thanks on advance, Serhiy.

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  • JSF, writeAttribute("value", str, null) fails with strings obtained through ValueExpression.getValue

    - by Roma
    Hello, I'm having a somewhat weird problem with custom JSF component. Here's my renderer code: public class Test extends Renderer { public void encodeBegin(final FacesContext context, final UIComponent component) throws IOException { ResponseWriter writer = context.getResponseWriter(); writer.startElement("textarea", component); String clientId = component.getClientId(context); if (clientId != null) writer.writeAttribute("name", clientId, null); ValueExpression exp = component.getValueExpression("value"); if (exp != null && exp.getValue(context.getELContext()) != null) { String val = (String) exp.getValue(context.getELContext()); System.out.println("Value: " + val); writer.writeAttribute("value", val, null); } writer.endElement("textarea"); writer.flush(); } } The code generates: <textarea name="j_id2:j_id12:j_id19" value=""></textarea> Property binding contains "test" and as it should be, "Value: test" is successfully printed to console. Now, if I change the code to: public void encodeBegin(final FacesContext context, final UIComponent component) throws IOException { ResponseWriter writer = context.getResponseWriter(); writer.startElement("textarea", component); String clientId = component.getClientId(context); if (clientId != null) writer.writeAttribute("name", clientId, null); ValueExpression exp = component.getValueExpression("value"); if (exp != null && exp.getValue(context.getELContext()) != null) { String val = (String) exp.getValue(context.getELContext()); String str = "new string"; System.out.println("Value1: " + val + ", Value2: " + str); writer.writeAttribute("value", str, null); } writer.endElement("textarea"); writer.flush(); } generated html is: <textarea name="j_id2:j_id12:j_id19" value="new string"></textarea> and console output is "Value1: test, Value2: new string" What's going on here? This doesn't make sense. Why would writeAttribute differentiate between the two strings? Additional info: The component extends UIComponentBase I am using it with facelets

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  • JMS - How do message selectors work with multiple queue and topic consumers?

    - by Stephen Harmon
    Say you have a JMS queue, and multiple consumers are watching the queue for messages. You want one of the consumers to get all of a particular type of message, so you decide to employ message selectors. For example, you define a property to go in your JMS message header named, "targetConsumer." Your message selector, which you apply to the consumer known as, "A," is something like "WHERE targetConsumer = "CONSUMER_A." It's clear that consumer A will now just grab messages with the property set like it is in in the example. Will the other consumers have awareness of that, though? IOW, will another consumer, unconstrained by a message selector, grab the "CONSUMER_A" messages, if it looks at the queue before Consumer A? Do I need to apply message selectors like, "WHERE targetConsumer < "CONSUMER_A" to the others? I am RTFMing and gathering empirical data now, but was hoping someone might know off the top of their head.

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  • How do I calculate a good hash code for a list of strings?

    - by Ian Ringrose
    Background: I have a short list of strings. The number of strings is not always the same, but are nearly always of the order of a “handful” In our database will store these strings in a 2nd normalised table These strings are never changed once they are written to the database. We wish to be able to match on these strings quickly in a query without the performance hit of doing lots of joins. So I am thinking of storing a hash code of all these strings in the main table and including it in our index, so the joins are only processed by the database when the hash code matches. So how do I get a good hashcode? I could: Xor the hash codes of all the string together Xor with multiply the result after each string (say by 31) Cat all the string together then get the hashcode Some other way So what do people think? (If you care we are using .NET and SqlServer)

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