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  • Java generic Interface performance

    - by halfwarp
    Simple question, but tricky answer I guess. Does using Generic Interfaces hurts performance? Example: public interface Stuff<T> { void hello(T var); } vs public interface Stuff { void hello(Integer var); <---- Integer used just as an example } My first thought is that it doesn't. Generics are just part of the language and the compiler will optimize it as though there were no generics (at least in this particular case of generic interfaces). Is this correct?

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  • Java - multithreaded access to a local value store which is periodically cleared

    - by Telax
    I'm hoping for some advice or suggestions on how best to handle multi threaded access to a value store. My local value storage is designed to hold onto objects which are currently in use. If the object is not in use then it is removed from the store. A value is pumped into my store via thread1, its entry into the store is announced to listeners, and the value is stored. Values coming in on thread1 will either be totally new values or updates for existing values. A timer is used to periodically remove any value from the store which is not currently in use and so all that remains of this value is its ID held locally by an intermediary. Now, an active element on thread2 may wake up and try to access a set of values by passing a set of value IDs which it knows about. Some values will be stored already (great) and some may not (sadface). Those values which are not already stored will be retrieved from an external source. My main issue is that items which have not already been stored and are currently being queried for may arrive in on thread1 before the query is complete. I'd like to try and avoid locking access to the store whilst a query is being made as it may take some time.

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  • Java How to find a value in a linked list iteratively and recursively

    - by Roxy
    Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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  • inputMismatchException Java reading doubles from plain text file

    - by user939287
    Using double variable = inputFile.nextDouble(); Gives the mismatch error and I can't figure out why... Anyone know what's up? The input file is just a bunch of doubles like 5.0... Okay here is the code snippet String fileName; Scanner scanner = new Scanner(System.in); System.out.println("\nEnter file name that contains the matrix and vector: "); fileName = scanner.nextLine(); Scanner inputFile = new Scanner(fileName); double a1 = inputFile.nextDouble(); the input file is a plain text document .txt in this format 5.0 4.0 -3.0 4.0 2.0 5.0 6.0 5.0 -2.0 -13.0 4.0 12.0 I don't understand why it wouldn't take those as doubles... As far as what its expecting the format of the file to be... I suppose binary? isn't that the default? I didn't specify in the code...

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  • Java split is eating my characters.

    - by Fenris_uy
    Hi, I have a string like this String str = "la$le\$li$lo". I want to split it to get the following output "la","le\$li","lo". The \$ is a $ escaped so it should be left in the output. But when I do str.split("[^\\\\]\\$") y get "l","le\$l","lo". From what I get my regex is matching a$ and i$ and removing then. Any idea of how to get my characters back? Thanks

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  • Framework for creating mock objects in Java

    - by Amir Rachum
    This is NOT a question about which is the best framework, etc. I have never used a mocking framework and I'm a bit puzzled by the idea. How does it know how to create the mock object? Is it done in runtime or generates a file? How do you know its behavior? And most importantly - what is the work flow of using such a framework (what is the step-by-step for creating a test). Can anyone explain? You can choose whichever framework you like for example, just say what it is.

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  • Simple stream read/write question in java

    - by Marius
    Hi, I'm trying to upload a file via URLConnection, but i need to read/write it as a binary file without any encoding changes. So i've tried to read byte[] array from FileInputStream, but now i have an issue. The PrintWriter object i use for outputing to the server does not allow me to do writer.write(content) (where content is of type byte[]). How can i fix this? Or is there another way to quickly copy binary data from a FileInputStream to a PrintWriter? Thank you

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  • URL decoding Japanese characters etc. in Java

    - by DanieL
    I have a servlet that receives some POST data. Because this data is x-www-form-urlencoded, a string such as ???? would be encoded to &#12469;&#12508;&#12486;&#12531;. How would I unencode this string back to the correct characters? I have tried using URLDecoder.decode("encoded string", "UTF-8"); but it doesn't make a difference. The reason I would like to unencode them, is because, before I display this data on a webpage, I escape & to &amp; and at the moment, it is escaping the &s in the encoded string so the characters are not showing up properly.

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  • Replace <Unknown Source> in Java Rhino (JSR223) with actual file name

    - by Lord.Quackstar
    Hello everyone, In my code, all of the scripts are contained in .js files. Whenever one of the scripts contains an error, I get this: javax.script.ScriptException: sun.org.mozilla.javascript.internal.EcmaError: ReferenceError: "nonexistant" is not defined. (<Unknown source>#5) in <Unknown source> at line number 5 What bugs me is the <Unknown Source>. Multiple files are in one ScriptContext, and it can be hard to track down an error. It also looks horrible. Is there a way to replace <Unknown Source> with the actual file name? None of the methods I see support passing a File object, so I'm really confused here.

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  • Create a java executable with Eclipse

    - by Micah
    This is a totally newbie question. I'm running Eclipse on Ubuntu. I created a test project that I want to compile to an executable (whataver the linux equivalent is of a Windows .exe file). Here's the contents of my program: public class MyTest { public static void main(String[] args) { System.out.println("You passed in: " + args[0]); } } I want to know how to compile it and then how to execute it from the command line. Thanks!

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  • How to validate overlapping no in java

    - by anandhinaveen
    I Have dynamically render row. WE have fields like FROM TO. For eg: From TO 2 10, 2 3, 8 12 It cannot accept this combination row.. That means no number should be overlapping. For eg: From TO 2 10, 0 1, 11 12 This combination is allowed.the row may also increased. I need need to write a validation for this overlapping. Can any 1 help to solve this problem.

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  • Java: Do something on event in SQL Database?

    - by wretrOvian
    Hello I'm building an application with distributed parts. Meaning, while one part (writer) maybe inserting, updating information to a database, the other part (reader) is reading off and acting on that information. Now, i wish to trigger an action event in the reader and reload information from the DB whenever i insert something from the writer. Is there a simple way about this? Would this be a good idea? : // READER while(true) { connect(); // reload info from DB executeQuery("select * from foo"); disconnect(); }

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  • JAVA setlayout(null)

    - by niv zatl
    I use setLayout (null) and I'm trying to place the buttons and textfield places I know by x, y The problem when I run the program no matter what software (Eclipse, bluej) I need to run on the panel with the mouse until I stand on the position of the button and I can see it. When I find the textfield, it is small and only when I start writing it became the size I set it Does anyone know how to solve it?

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  • Get file full path in java

    - by c0mrade
    When I pass File file to a method I'm trying to get its full path like file.getAbsolutePath(); I always get the same result no matter which one I use either absolute or canonical path PATH_TO_MY_WORKSPACE/projectName/filename and it is not there, how can I get exact location of the file? Thank you

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  • java multiple connections between server and one client

    - by user1507128
    I'm trying to make like a skype-instant messager, my idea for it is to have one server which handles multiple connections for the clients. What I now have is a friend list etc, but now I want to create Threads both for server and client to handle a conversation. The problem is that I need multiple connections between a server and one client for every conversation(I think). but i dont think it's possible. Does someone have another way for doing this or maybe a way to make multiple connections between the server and a client? Thanks for helping me out PS: English is not my main language so please excuse me for my grammar.

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  • List files starting with a specific name using java

    - by user3610075
    i want to list files starting with a name like "Report" from a folder. i found this in google to list all files but i don't how to list file starting with a name. Thank you File directory = new File("C:\\Users\\kiki\\Downloads"); File[] files = directory.listFiles(); for (int index = 0; index < files.length; index++) { //Print out the name of files in the directory System.out.println(files[index].toString()); }

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  • question about prefix and suffix in java

    - by kate
    hi!!I have an issue and i want your help!I have a specific REGEX which i have named it "unique" and i want to store the data that it gives me!! The prefix and the suffix of this regex!!so!!someone has told me to use var prefix and var suffix but i don't know how to do it! for your convinience i give u my xml for this regex <reg name="unique"> <start><![CDATA[ <!-- 72 HOURS FORECASTS --> ]]></start> <end><![CDATA[<!-- 72 HOURS FORECASTS -->]]></end> </reg> the code where i call this regex is int k = 0; for(Xml reg_is:fetchsite.child("site").child("regexps").children("reg")) { if(reg_is.string("name").contains("unique")){ if(reg_is.child("start").content()=="") error += "\tNo prefix reg.exp. given.\n"; else prefix = HtmlMethods.removeBreaks(replaceVariables(reg_is.child("start").content())); if(reg_is.child("end").content()=="") error += "\tNo suffix reg.exp. given.\n"; else suffix = HtmlMethods.removeBreaks(replaceVariables(reg_is.child("end").content())); } else{ poleis[k][0]= HtmlMethods.removeBreaks(reg_is.string("name")); poleis[k][1] = HtmlMethods.removeBreaks(replaceVariables(reg_is.child("start").content())); poleis[k][2] = HtmlMethods.removeBreaks(replaceVariables(reg_is.child("end").content())); k++; }

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  • Open a new panel via a button Java Swing

    - by abuteau
    I saw a lot of post on StackOverflow relating to this, but unable to solve my problem. I want to open a new Panel by clicking a button. Here is how i try to do it parameterButton = new JButton("Parametres"); parameterButton.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ createParameterPanel = new DisplayParameterPanel(); createParameterPanel.setVisible(true); add(createParameterPanel); }; }); add(parameterButton); When I click the parameterButton it doesn't open. How can I open a new panel. Thanks,

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  • Getter/Setter Problem in Java?

    - by Praveen Chandrasekaran
    Hi Folks, I want to pass the String value between the classes both are same package. so i created the the classs like the code: public class Map_Delegate { String myLatitude; String myLongitude; String myName; private String TAG = "Map_Delegate"; public String getMyName() { return this.myName; } public void setMyName(String value) { Log.v(TAG, value); this.myName = value; } public String getMyLatitude() { return this.myLatitude; } public void setMyLatitude(String value) { Log.v(TAG, value); this.myLatitude = value; } public String getMyLongitude() { return this.myLongitude; } public void setMyLongitude(String value) { Log.v(TAG, value); this.myLongitude = value; } } But it can't pass the value. I done like this code to set the value: Map_Delegate map = new Map_Delegate(); map.setMyName(first_name_temp + " " + last_name_temp); map.setMyLatitude(homeLatitude_temp); map.setMyLongitude(homeLongitude_temp); code to get the value: Map_Delegate map = new Map_Delegate(); name_val = getMyName(); lat_val = getMyLatitude(); long_val = getMyLongitude(); Why get the Null value can you Guess? All classes in the same package and public .AnyIdea?

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  • Convert any object to pretty HTML in java

    - by ripper234
    How can I convert a given object (in a generic way with reflection) to pretty printable HTML? What ready made library do you recommend that does this? I need support for simple nested objects (as long as they don't create loops in the object graph). I tried to convert it to JSON, but DefaultPrettyPrinter is not HTML friendly.

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  • Java: empty ArrayLists in a foor loop

    - by Patrick
    hi, I'm reusing the same ArrayList in a for loop, and I use for loop results = new ArrayList<Integer>(); experts = new ArrayList<Integer>(); output = new ArrayList<String>(); .... to create new ones. I guess this is wrong, because I'm allocating new memory. Is this correct ? If yes, how can I empty them ? Added: another example I'm creating new variables each time I call this method. Is this good practice ? I mean to create new precision, relevantFound.. etc ? Or should I declare them in my class, outside the method to not allocate more and more memory ? public static void computeMAP(ArrayList results, ArrayList experts) { //compute MAP double precision = 0; int relevantFound = 0; double sumprecision = 0; thanks

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