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  • Is HashMap in Java collision safe

    - by changed
    Hi I am developing a parser that needs to put key value pairs in hashmap. But a key can have multiple values which i can do in this way HashMap<String,ArrayList<String>> . But what happens if number of keys are very large and it start matching with other key's hashcode. Will that rewrite previous key's value ? thanks -devSunday

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  • Best Java library(ies) for forgiving command interpreter

    - by vkraemer
    I am looking for a library or set of libraries that will help me write a forgiving command interpreter. A forgiving command interpreter would be a command interpreter which can deal with simple and even not so simple spelling and word order mistakes in the input. My goal is to have an interpreter which would take the input (a command) from a user and then: execute the command, if it is correct. apply corrections to the command, until a correct command is generated and then present that command to the user to confirm whether it is 'what the user meant'.

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  • Java Swing how to create a task reminder

    - by newbie123
    How to create a event reminder. Example, an user created an event which is today 5.00pm and stored it into database. When ruun the program the reminder will pop up if the system time is 5.00pm. Is there any API can do that? From google what I got was those freeware.

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  • java web templates across multiple WAR files

    - by Casey
    I have a multi WAR web application that was designed badly. There is a single WAR that is responsible for handling some authorization against a database and defines a standard web page using a jsp taglib. The main WAR basically checks the privileges of the user and than based on that, displays links to the context path of the other deployed WARS. Each of the other deployed WARs includes this custom tag lib. I am working on redesigning this application, and one of the nice things that I want to retain is that we have other project teams that have developed these WAR modules that "plug into" our current system to take advantage of other things we have to offer. I am not entirely sure how to handle the page templates though. I need a templating system that would be easy enough to use across multiple wars (I was thinking of jsp fragments??). I really only need to define a consistent header and main navigation section. Whatever else is displayed on the page is up to the individual web project. Any suggestions? I hope that this is clear, if not I can elaborate more.

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  • Extracting user-friendly exception details in Java

    - by Jon
    I've got a J2EE web application that I'm working on and when an exception occurs, I'd like to get some basic details about the exception and log it. The message that I'm logging should be pretty basic, something that might mean something to the people running the web server(s). Would using e.getMessage() be the best thing to log? Thanks.

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  • Java - Thread safety of ArrayList constructors

    - by andy boot
    I am looking at this piece of code. This constructor delegates to the native method "System.arraycopy" Is it Thread safe? And by that I mean can it ever throw a ConcurrentModificationException? public Collection<Object> getConnections(Collection<Object> someCollection) { return new ArrayList<Object>(someCollection); } Does it make any difference if the collection being copied is ThreadSafe eg a CopyOnWriteArrayList? public Collection<Object> getConnections(CopyOnWriteArrayList<Object> someCollection) { return new ArrayList<Object>(someCollection); }

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  • Update music file details - Java.

    - by Desorder
    Hi all, Well, I'm a music fan guy, and now with my 18000 music collection, it's getting very hard to maintain. So, I would like to ask I could of question to help to write an app to maintain it for me. 1- How can I access a music file and read details of it? I mean, I would like to write some code and passing the directory, my app would read all the music files (understand mp3 files) and with that I would like to access details like title, artist, length and so on... 2- Is there a public source that I could access and update my file? A webservice somewhere that I could connect, query some information based on song name, or artist or whatever. I would like to achieve a final result of given a directory, my app would read the file, collect some information and query the source for a complete list of detail and update my file. Thank you guys for any help...

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  • How to concatenate int values in java?

    - by Shamli
    hi, I have the following values: int a=1; int b=0; int c=2; int d=2; int e=1; How do i concatenate these values so that i end up with a String that is 10221; please note that multiplying a by 10000, b by 1000.....and e by 1 will not working since b=0 and therefore i will lose it when i add the values up. Thnks you in advance.

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  • Assigning int to byte in java?

    - by user303218
    int val =233; byte b = (byte)val; System.out.println(b); I have a simple case, like one integer with some value & i want to convert that value & place in the byte type for output. But in this case negative value is coming? How to successfully place the int value to byte type.

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  • how does serializable work in java?

    - by Karl Trumstedt
    If I have an instance of a class that I store in a session I need to make it serializable. This class has a static variable, will this be serialized in every instance stored? The static variable is a reference to a cache containing a lot of data in the background. Will all of this data be serialized? If so, it seems preferable to make this variable transient and re-fetch the cache instance each time the instance is restored. Maybe not store the cache instance at all in the class. Will the constructor execute when a class is restored from a serialized state? if not is there any other method I can use to re-instate a transient variable?

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  • Java String object creation

    - by Ajay
    Hi, 1) What is difference in thers two statements: String s1 = "abc"; and String s1 = new String("abc") 2) as i am not using new in first statement, how string object will be created Thanks

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  • Reading lines of data from text files using java

    - by razshan
    I have a text file with x amount of lines. each line holds a integer number. When the user clicks a button, an action is performed via actionlistener where it should list all the values as displayed on the text file. However, right now I have linenum set to 10 implying I already told the code that just work with 10 lines of the text file. So, if my text file has only 3 rows/lines of data...it will list those lines and for rest of the other 7 lines, it will spit out "null". I recall there is a way to use ellipsis to let the program know that you don't know the exact value but at the end it calculates it based on the given information. Where my given information will the number of lines with numbers(data). Below is part of the code. private class thehandler implements ActionListener{ public void actionPerformed(ActionEvent event){ BufferedReader inputFile=null; try { FileReader freader =new FileReader("Data.txt"); inputFile = new BufferedReader(freader); String MAP = ""; int linenum=10; while(linenum > 0) { linenum=linenum-1; MAP = inputFile.readLine();//read the next line until the specfic line is found System.out.println(MAP); } } catch( Exception y ) { y.printStackTrace(); } }}

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  • StringBufferInputStream Question in Java

    - by JJG
    I want to read an input string and return it as a UTF8 encoded string. SO I found an example on the Oracle/Sun website that used FileInputStream. I didn't want to read a file, but a string, so I changed it to StringBufferInputStream and used the code below. The method parameter jtext, is some Japanese text. Actually this method works great. The question is about the deprecated code. I had to put @SuppressWarnings because StringBufferInputStream is deprecated. I want to know is there a better way to get a string input stream? Is it ok just to leave it as is? I've spent so long trying to fix this problem that I don't want to change anything now I seem to have cracked it. @SuppressWarnings("deprecation") private String readInput(String jtext) { StringBuffer buffer = new StringBuffer(); try { StringBufferInputStream sbis = new StringBufferInputStream (jtext); InputStreamReader isr = new InputStreamReader(sbis, "UTF8"); Reader in = new BufferedReader(isr); int ch; while ((ch = in.read()) > -1) { buffer.append((char)ch); } in.close(); return buffer.toString(); } catch (IOException e) { e.printStackTrace(); return null; } }

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  • Java Swing popup visibility

    - by Octavio
    Why a popup created like this is shown in front of all windows applications with JRE 1.6.0_18 but it doesn't using 1.6.0_03 ? PopupFactory popupFactory = new PopupFactory(); Popup popup= popupFactory.getPopup(null,new JPanel(),200,200); popup.show();

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  • How to make sketching kind module in java?

    - by Nitz
    Hey Guys I am trying to make one software on which user can make any sketch and make any drawing kind of thing. i am trying to get reference from this two great software. 1. Notelab 2. Jarnal But both having great and many facility in it. But In my software i want only sketching-drawing, so how to do that? I tried to use Canvas but i don't get how to use it?

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  • interface as a method parameter in Java

    - by PeterYu
    Hi all, I had an interview days ago and was thrown a question like this. Q: Reverse a linked list. Following code is given: public class ReverseList { interface NodeList { int getItem(); NodeList nextNode(); } void reverse(NodeList node) { } public static void main(String[] args) { } } I was confused because I did not know an interface object could be used as a method parameter. The interviewer explained a little bit but I am still not sure about this. Could somebody enlighten me?

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  • Validating IPv4 string in Java

    - by Mat Banik
    Bellow method is validating if string is correct IPv4 address it returns true if it is valid. Any improvements in regex and elegance would be very appreciated: public static boolean validIP(String ip) { if (ip == null || ip.isEmpty()) return false; ip = ip.trim(); if ((ip.length() < 8) & (ip.length() > 15)) return false; try { Pattern pattern = Pattern.compile("^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$"); Matcher matcher = pattern.matcher(ip); return matcher.matches(); } catch (PatternSyntaxException ex) { return false; } }

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  • [Java] Safe way of exposing keySet().

    - by Jake
    This must be a fairly common occurrence where I have a map and wish to thread-safely expose its key set: public MyClass { Map<String,String> map = // ... public final Set<String> keys() { // returns key set } } Now, if my "map" is not thread-safe, this is not safe: public final Set<String> keys() { return map.keySet(); } And neither is: public final Set<String> keys() { return Collections.unmodifiableSet(map.keySet()); } So I need to create a copy, such as: public final Set<String> keys() { return new HashSet(map.keySet()); } However, this doesn't seem safe either because that constructor traverses the elements of the parameter and add()s them. So while this copying is going on, a ConcurrentModificationException can happen. So then: public final Set<String> keys() { synchronized(map) { return new HashSet(map.keySet()); } } seems like the solution. Does this look right?

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  • Java Timer not working

    - by Jacob
    I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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  • Java: Comparing a class with another within that class using a my own .equals

    - by user1670252
    I am making a method .equals replacing the equals method used. It accepts a object. I want it to check if that object equals the class that runs the .equals class. I know I want to compare all the private methods I have to that object. Is there a way to do this without making another private class to get the private variables from the object? How do I do this to compare equality not identity? I am stuck on this. Do i have to use == to compare? Also looking online i see others use recursion. If this is the way i have to do it can you show and explain it to me? so an example i have public boolean equals(Object o) { this is in a class we will call bobtheBuilder (first thing to pop in my head) I want to check if the object o is equal to the class he has private object array and a private int. I assume I want to check if the array and int of this class equal the array and int of the object.

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  • Java : Singleton class instances in a Web based Application

    - by Preethi Jain
    I have this Singleton class inside a Web Application . public class MyDAO { private static MyDAO instance; private MyDAO() { } public static MyDAO getInstance() { if (instance == null) { instance = new MyDAO(); } return instance; } I will access it this way public void get_Data() { MyDAO dao = MyDAO.getInstance(); } How many Objects of MyDAO class will be created if there are 3 Users accessing the Application ?? Will there be one instance of MyDAO per User ??

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  • Java - understanding servlets

    - by Trup
    I am working on a homework project that should implement a board game between 2 clients over an HttpServlet. I have couple of questions: 1) I read that HttpServlets must be stateless, however, for the sake of the game, I have to keep a lot of state(whose turn it is, the state of the board, etc). Do I have to keep this in the clients? Does the HttpServlet indeed have to be stateless, i.e. have no fields that track state? 2) I know that the clients will talk to the servlet via the doGet/doPost methods, but how can the servlet talk to the clients(for example, if player 1 just made a move and sent it to the servlet, the servlet has to tell client 2 what the move was). Thank you Also, if you can point me to a useful, simple example of a similar code online, I would be very grateful

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