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  • Declare java enum with a String array

    - by chama
    I'm trying to declare an enum type based on data that I'm retrieving from a database. I have a method that returns a string array of all the rows in the table that I want to make into an enumerated type. Is there any way to construct an enum with an array? This is what I tried, but from the way it looked in eclipse, it seemed like this just created a method by that name: public enum ConditionCodes{ Condition.getDescriptions(); } Thank you in advance!

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  • Using enums in Java across multiple classes

    - by Richard Mar.
    I have the following class: public class Card { public enum Suit { SPACES, HEARTS, DIAMONDS, CLUBS }; public Card(Suit nsuit, int nrank) { suit = nsuit; rank = nrank; } private Suit suit; private int rank; } I want to instantiate it in another class, but that class doesn't understand the Suit enum. Where should I put the enum to make it publicly visible?

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  • Java - String Pool

    - by Gogi
    What is meant by String Pool ? What is difference between the following declarations : String s="hello"; String s=new String("hello"); Is there any difference between the Storing of this two strings by JVM ?

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  • Java Null Pointer Exception :-(

    - by John-Michael Reed
    I've got a Null Pointer Exception in my main that just won't go away and I'm totally out of ideas. The error is on the line "Board[x][y].color = 2;" in which Board is a public, static array of piece objects that contain instance variables like the one "color" that is being set to 2 in the above statement. Pieces is not static - that is there are many different copies of pieces, each with its own data, but only one board. The array has been initialized and defined as both public Piece[][] Board = new Piece[8][8] and public static Piece[][] Board = new Piece[8][8], but no matter how I mess around with it (getting rid of static, putting the variable in another object, etc.), I can't seem to get the error to go away. Help?

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  • Hiding "Print to file" in a Java print dialog

    - by Carl Smotricz
    I'm maintaining this Swing app that has a "print" option. Users need to be kept from interacting in any way with the underlying file system, but the print dialog offers "print to file" as one printer, and that of course allows selecting a directory and file from the file system. Is there a painless way to override/modify the print dialog to hide the "to file" printer from this dialog? I understand the API will let me do this piecemeal but I'd rather not have to re-create most of the dialog GUI and functionality to do this.

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  • this and super in java

    - by abson
    this and super are keywords isn't it, then how can we use them for passing arguments to constructors the same way as with a method?? In short how is it that these can show such distinct behaviours??

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  • Java Detect Variable Change Using PropertyChangeSupport and PropertyChangeListener

    - by Sam
    I'm trying to print out debug statements when some third party code changes a variable. For example, consider the following: public final class MysteryClass { private int secretCounter; public synchronized int getCounter() { return secretCounter; } public synchronized void incrementCounter() { secretCounter++; } } public class MyClass { public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // add code here to detect calls to incrementCounter and print a debug message } I don't have the ability to change the 3rd party MysteryClass, so I thought that I could use PropertyChangeSupport and PropertyChangeListener to detect changes to the secretCounter: public class MyClass implements PropertyChangeListener { private PropertyChangeSupport propertySupport = new PropertyChangeSupport(this); public MyClass() { propertySupport.addPropertyChangeListener(this); } public void propertyChange(PropertyChangeEvent evt) { System.out.println("property changing: " + evt.getPropertyName()); } public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // do logic which involves increment and getting the value of MysteryClass } } Unfortunately, this did not work and I have no debug messages printed out. Does anyone see what is wrong with my implementation of the PropertyChangeSupport and Listener interfaces? I want to print a debug statement whenever incrementCounter is called or the value of secretCounter changes.

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  • JAVA: multiple files download at the same time?

    - by user319096
    hi guys, Is there any methods for downloading multiple files at the same time? That is, after select multiple files, click the download button, and choose the destination directory, the files selected will be downloaded at the same time. i googled it and not find any solutions, can anybody know? im using struts1 and spring2.

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  • Java giving incorrect year values

    - by whistler
    Something very, very strange is occurring in my program, and I'm wondering if anyone out there has seen this occur before. And, if so, how to fix it. Basically, I am parsing an csv file...no problem there. One column contains a date and I am taking it in as a String and changing to a Date object. Again, no problem there. The code is as follows: SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yy hh:mm"); Date initialDate = new Date(); try { initialDate = dateFormat.parse(rows.get(0)[8]); System.out.println(initialDate); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } Of course, I'm parsing other columns as well (and those are working fine). So, when I run my program for a small csv file (2.8 MB), the dates come out (i.e. are parsed) perfectly. However, when I run the program for a large csv file (25 MB), the dates are a hot mess. For example, take a look at the year values I am getting (the following is just a tiny portion of the println output from the code above): 1000264 at Sun Nov 05 15:30:00 EST 2186 1000320 at Sat Mar 04 17:30:00 EST 2169 1000347 at Sat Apr 01 09:45:00 EDT 2169 1000413 at Tue Jul 09 13:00:00 EDT 2182 1000638 at Fri Dec 11 13:45:00 EST 2167 1000667 at Wed Dec 10 10:00:00 EST 2188 1000690 at Mon Jan 02 13:00:00 EST 2169 1000843 at Thu Feb 11 13:30:00 EST 2196 In actuality, the years are in the realm of 1990-2006 or so. Again, this does not happen with the small csv file. Does anyone know what's going on here and how I can fix it? I need to process the large csv file (the small one was just for testing purposes). By request, here are the actual dates in the csv file and after that the value given by the code above: 5/20/03 15:30 5/20/03 15:30 8/30/04 9:00 8/30/04 9:00 12/20/04 10:30 12/20/04 10:30 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Thu Dec 08 09:00:00 EST 2196 Tue Dec 12 10:30:00 EST 2186 Tue Dec 12 10:30:00 EST 2186

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  • Java - Does null variable require space in memory

    - by Yatendra Goel
    class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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  • Reference variable to an object instantiated/initialized in another class in Java

    - by Alex
    The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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  • What is a good "Error Checking" Pattern (Java)?

    - by Jack
    I'll explain what I mean by input error checking. Say you have a function doSomething(x). If the function completes successfully doSomething does something and returns nothing. However, if there are errors I'd like to be notified. That is what I mean by error checking. I'm looking for, in general, the best way to check for errors. I've thought of the following solutions, each with a potential problem. Flag error checking. If doSomething(x) completes successfully return null. Otherwise, it returns a boolean or an error string. Problem: Side effects. Throwing an exception. Throw an exception if doSomething(x) encounters an error. Problem: If you are performing error checking for parameters only, throwing an IllegalArgumentExceptionseems inappropriate. Validating input prior to function call. If the error checking is only meant for the parameters of the function, then you can call a validator function before calling the doSomething(x) function. Problem: What if a client of the class forgets to call the validator function before calling doSomething(x)? I often encounter this problem and any help or a point in the right direction would be much appreciated.

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  • converting a UTC time to a local time zone in Java

    - by aloo
    I know this subject has been beaten to death but after searching for a few hours to this problem I had to ask. My Problem: do calculations on dates on a server based on the current time zone of a client app (iphone). The client app tells the server, in seconds, how far away its time zone is away from GMT. I would like to then use this information to do computation on dates in the server. The dates on the server are all stored as UTC time. So I would like to get the HOUR of a UTC Date object after it has been converted to this local time zone. My current attempt: int hours = (int) Math.floor(secondsFromGMT / (60.0 * 60.0)); int mins = (int) Math.floor((secondsFromGMT - (hours * 60.0 * 60.0)) / 60.0); String sign = hours > 0 ? "+" : "-"; Calendar now = Calendar.getInstance(); TimeZone t = TimeZone.getTimeZone("GMT" + sign + hours + ":" + mins); now.setTimeZone(t); now.setTime(someDateTimeObject); int hourOfDay = now.get(Calendar.HOUR_OF_DAY); The variables hour and mins represent the hour and mins the local time zone is away from GMT. After debugging this code - the variables hour, mins and sign are correct. The problem is hourOfDay does not return the correct hour - it is returning the hour as of UTC time and not local time. Ideas?

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  • Revalidate and repaint - Java Swing

    - by bosra
    I have a JPanel that I am adding JLabel's to. I then want to remove all the JLabels and add some new ones. So I do the following: panel.removeAll();panel.repaint(); panel.add(new JLabel("Add something new"); panel.revalidate(); This works fine. My problem arises when I start a new thread after this like: panel.removeAll();panel.repaint(); (1)panel.add(new JLabel("Add something new"); panel.revalidate(); //new thread to start - this thread creates new JLabels that should appear under (1) firstProducer.start(); try { firstProducer.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Then the output from the original JLabels is still visible. I have read that the revalidate process is a long running task and hence the firstProducer thread is getting started while the revalidation is going on and a conflict is arising. What is the best way to deal with this?

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  • Regex to match a Java method signature

    - by nitesh
    I am having this particular requirement where a method has to be identified by different regular expressions for different components. For example, there need to be a regex for return parameter, one for method name, one for argument type and one for argument name. I was able to come up with an expression till this step as follows - ([^,]+) ([^,]+)\((([^,]+) ([^,]+))\) It works well for a method signature like - ReturnType foo(Arg parameter) The regular expression identifies ReturnType, foo, Arg and parameter separately. Now the problem is that a method can have no/one/multiple arguments separated by commas. I am not able to get a repeating expression for this. Help will be appreciated.

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  • java - Depth First Search - Perform DFS on a tree

    - by DJDonaL3000
    Im trying to perform DFS on a Minimum Spanning Tree which contains 26 nodes. Nodes are named 'A' to 'Z' and the tree is undirected. I have an empty function called DFS here that I am trying to write, which (i presume) takes in the tree (a 2D array) a startNode (randomly selected node 'M') and the endNode (randomly selected node 'Z'). The weights of connected nodes are identified in the 2D array parameter, but how do I actually get started visiting nodes? All that is required is to print each nodeName in the order of the DFS traversal. Do I need to create a Node_class for each node in the 2d array??

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  • JAVA: How do I accept input during a certain period of time only

    - by sebrock
    Im trying to do a simple game where I continually need input from players. This needs to happen during a certain time period only. Everything that is sent after that will be discarded. After the time period a new game starts. So: Start game Wait for input from all players during 10 seconds 10 secs no more input Calculate the winner and do some stuff Goto 1. I was thinking using a timer and timertask to keep track of time and maybe use a boolean variable that changes from "open" to "closed" after 10 seconds? Please give me some advise on this.

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  • Adapting pseudocode to java implementation for finding the longest word in a trie

    - by user1766888
    Referring to this question I asked: How to find the longest word in a trie? I'm having trouble implementing the pseudocode given in the answer. findLongest(trie): //first do a BFS and find the "last node" queue <- [] queue.add(trie.root) last <- nil map <- empty map while (not queue.empty()): curr <- queue.pop() for each son of curr: queue.add(son) map.put(son,curr) //marking curr as the parent of son last <- curr //in here, last indicate the leaf of the longest word //Now, go up the trie and find the actual path/string curr <- last str = "" while (curr != nil): str = curr + str //we go from end to start curr = map.get(curr) return str This is what I have for my method public static String longestWord (DTN d) { Queue<DTN> holding = new ArrayQueue<DTN>(); holding.add(d); DTN last = null; Map<DTN,DTN> test = new ArrayMap<DTN,DTN>(); DTN curr; while (!holding.isEmpty()) { curr = holding.remove(); for (Map.Entry<String, DTN> e : curr.children.entries()) { holding.add(curr.children.get(e)); test.put(curr.children.get(e), curr); } last = curr; } curr = last; String str = ""; while (curr != null) { str = curr + str; curr = test.get(curr); } return str; } I'm getting a NullPointerException at: for (Map.Entry<String, DTN> e : curr.children.entries()) How can I find and fix the cause of the NullPointerException of the method so that it returns the longest word in a trie?

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  • force warning in java

    - by Dustin Getz
    I'd like a mechanism to throw a compile-time warning manually. I'm using it to flag unfinished code so I can't possibly forget about it later. @Deprecated is close but warns at caller site, not at creation site. I'm using eclipse. Something like #Warning in C#.

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  • Singleton & Multithreading in Java

    - by vivek jagtap
    What is the preferred way to work with Singleton class in multithreaded environment? Suppose if I have 3 thread, and all they try to access getInstance() method of singleton class at the same time - What would happen if no synchronization is maintained? Is it good practice to use synchronized getInstance() method or use synchronized block inside getInstance(). Please advise if there is any other way out.

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  • Java, merging two arrays evenly

    - by user2435044
    What would be the best way to merge two arrays of different lengths together so they are evenly distributed in the new array? Say I have the following arrays String[] array1 = new String[7]; String[] array2 = new String[2]; String[] mergedArray = new String[array1.length + array2.length]; I would want mergedArray to have the following elements array1 array1 array1 array2 array1 array1 array1 array2 array1 but if I were to change the size of the arrays to String[] array1 = new String[5]; String[] array2 = new String[3]; String[] mergedArray = new String[array1.length + array2.length]; then I would want it to be array1 array2 array1 array2 array1 array2 array1 array1 basically if it can be helped each array2 element shouldn't be touching each other; exception if array2 has a size larger than array1.

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