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  • Modifying annotation attribute value at runtime in java

    - by Lici
    Hi folks: some methods in our model pojos have been annotated like this: @Column(name="cli_clipping_id", updatable=false, columnDefinition = "varchar(" + ModelUtils.ID_LENGTH + ") COLLATE utf8_bin") columnDefinition attribute is database vendor dependant, so when trying to drop schema in HSQLDB using Hibernate it fails: [ERROR] 16 jun 12:58:42.480 PM main [org.hibernate.tool.hbm2ddl.SchemaExport] Unexpected token: COLLATE in statement [create table cms.edi_editorial_obj (edi_uuid varchar(23) COLLATE ] To fix this, i'm thinking on this solution (but don't want to spend time if it isn't possible) , at runtime, for each method column annotated: Get @Column annotation Create a copy of the column annotation, setting columnDefinition null using javaassist. set column method annotation to the copy column annotation object overriding the old one (i don't know it this is possible) Is it possible to "hack" these methods this way? Any help would be much appreciated ...

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  • java number exceeds long.max_value - how to detect?

    - by jurchiks
    I'm having problems detecting if a sum/multiplication of two numbers exceeds the maximum value of a long integer. Example code: long a = 2 * Long.MAX_VALUE; System.out.println("long.max * smth > long.max... or is it? a=" + a); This gives me -2, while I would expect it to throw a NumberFormatException... Is there a simple way of making this work? Because I have some code that does multiplications in nested IF blocks or additions in a loop and I would hate to add more IFs to each IF or inside the loop. Edit: oh well, it seems that this answer from another question is the most appropriate for what I need: http://stackoverflow.com/a/9057367/540394 I don't want to do boxing/unboxing as it adds unnecassary overhead, and this way is very short, which is a huge plus to me. I'll just write two short functions to do these checks and return the min or max long. Edit2: here's the function for limiting a long to its min/max value according to the answer I linked to above: /** * @param a : one of the two numbers added/multiplied * @param b : the other of the two numbers * @param c : the result of the addition/multiplication * @return the minimum or maximum value of a long integer if addition/multiplication of a and b is less than Long.MIN_VALUE or more than Long.MAX_VALUE */ public static long limitLong(long a, long b, long c) { return (((a > 0) && (b > 0) && (c <= 0)) ? Long.MAX_VALUE : (((a < 0) && (b < 0) && (c >= 0)) ? Long.MIN_VALUE : c)); } Tell me if you think this is wrong.

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • java servlet: generate zip file from BLOBs

    - by Zack
    I'm trying to zip a large number of pdf files (stored as BLOBs in the DB) and then return the zip as an attachment to the user. What's the best way to do this without running into memory issues? Another note: I actually need to merge some PDFs prior to adding them to the ZipOutputStream. Therefore, a couple PDFs will need to be stored in memory at a time. I assume it would be best to then store them as temporary files on the server before zipping them all?

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  • Gracefully avoiding NullPointerException in Java

    - by Yuval A
    Consider this line: if (object.getAttribute("someAttr").equals("true")) { // .... Obviously this line is a potential bug, the attribute might be null and we will get a NullPointerException. So we need to refactor it to one of two choices: First option: if ("true".equals(object.getAttribute("someAttr"))) { // .... Second option: String attr = object.getAttribute("someAttr"); if (attr != null) { if (attr.equals("true")) { // .... The first option is awkward to read but more concise, while the second one is clear in intent, but verbose. Which option do you prefer in terms of readability?

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  • quick java question

    - by j-unit-122
    private static char[] quicksort (char[] array , int left , int right) { if (left < right) { int p = partition(array , left, right); quicksort(array, left, p - 1 ); quicksort(array, p + 1 , right); } for (char i : array) System.out.print(i + ” ”); System.out.println(); return array; } private static int partition(char[] a, int left, int right) { char p = a[left]; int l = left + 1, r = right; while (l < r) { while (l < right && a[l] < p) l++; while (r > left && a[r] >= p) r--; if (l < r) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } } a[left] = a[r]; a[r] = p; return r; } } hi guys just a quick question regarding the above coding, i know that the above coding returns the following B I G C O M P U T E R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M P U T O R B C E G I M O P T U R B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U B C E G I M O P R T U when the sequence BIGCOMPUTER is used but my question is can someone explain to me what is happening in the code and how? i know abit about the quick-sort algorithm but it doesnt seem to be the same in the above example.

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  • Blackberry (Java) - Drawing graphics on top of rendered text/buttons etc

    - by paullb
    Based off the one of the demos I have the following code. Currently what displays in the simulator is just hte contents of the paint function, however the ObjectChoiceField is still selectable if one happens to click in the right location. I would like both the text contents and the paint function contents to appear. Is this possible? public CityInfoScreen() { //invoke the MainScreen constructor super(); //add a screen title LabelField title = new LabelField("City Information Kiosk", LabelField.ELLIPSIS | LabelField.USE_ALL_WIDTH); setTitle(title); //add a text label add(new RichTextField("Major U.S. Cities")); //add a drop-down list with three choices: //Los Angeles, Chicago, or New York //... String choices[] = {"Los Angeles","Chicago","New York"}; choiceField = new ObjectChoiceField("select a city", choices); add(choiceField); Manager man = this.getMainManager(); } ... public void paint(Graphics g){ super.paint(g); // g.drawRect(0,left,500,500+left); g.setGlobalAlpha(0); g.drawRect(100-left,100-top,200,200); String text = new Integer(left).toString(); String text2 = new Integer(top).toString(); g.drawText(text + " " + text2,120-left,120-top); }

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  • Have threads run indefinitely in a java application

    - by TP
    I am trying to program a game in which I have a Table class and each person sitting at the table is a separate thread. The game involves the people passing tokens around and then stopping when the party chime sounds. how do i program the run() method so that once I start the person threads, they do not die and are alive until the end of the game One solution that I tried was having a while (true) {} loop in the run() method but that increases my CPU utilization to around 60-70 percent. Is there a better method?

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  • Java: Make a method abstract for each extending class

    - by Martijn Courteaux
    Hi, Is there any keyword or design pattern for doing this? public abstract class Root { public abstract void foo(); } public abstract class SubClass extends Root { public void foo() { // Do something } } public class SubberClass extends SubClass { // Here is it not necessary to override foo() // So is there a way to make this necessary? // A way to obligate the developer make again the override } Thanks

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  • Java convert JSONObject to URL parameter

    - by Alex Ivasyuv
    What is the elegant way to convert JSONObject to URL parameters. For example, JSONObject: {stat: {123456: {x: 1, y: 2}, 123457: {z: 5, y: 2}}}} this should be like: stat[123456][x]=1&stat[123456][y]=2&stat[123457][z]=5&stat[123457][y]=2 of course with escaped symbols, and of course JSON object could be more complicated.. Maybe there already exist some mechanisms for that? Thanks,

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  • How to keep Java Frame from waiting?

    - by pypmannetjies
    I am writing a genetic algorithm that approximates an image with a polygon. While going through the different generations, I'd like to output the progress to a JFrame. However, it seems like the JFrame waits until the GA's while loop finishes to display something. I don't believe it's a problem like repainting, since it eventually does display everything once the while loop exits. I want to GUI to update dynamically even when the while loop is running. Here is my code: while (some conditions) { //do some other stuff gui.displayPolygon(best); gui.displayFitness(fitness); gui.setVisible(true); } public void displayPolygon(Polygon poly) { BufferedImage bpoly = ImageProcessor.createImageFromPoly(poly); ImageProcessor.displayImage(bpoly, polyPanel); this.setVisible(true); } public static void displayImage(BufferedImage bimg, JPanel panel) { panel.removeAll(); panel.setBounds(0, 0, bimg.getWidth(), bimg.getHeight()); JImagePanel innerPanel = new JImagePanel(bimg, 25, 25); panel.add(innerPanel); innerPanel.setLocation(25, 25); innerPanel.setVisible(true); panel.setVisible(true); }

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  • Blackberry (Java) - Can't get KeyListener to work

    - by paullb
    I am trying to get the KeyListener working for Blackberry, but none of the Dialogs pop up indicating that a key has been pressed (see code below, each action has a dialog popup in them). Any ideas on what i might be doing wrong? public class CityInfo extends UiApplication implements KeyListener { static CityInfo application; public static void main(String[] args) { //create a new instance of the application //and start the application on the event thread application.enterEventDispatcher(); } public CityInfo() { //display a new screen application = new CityInfo(); pushScreen(new WorkflowDisplayScreen()); this.addKeyListener(this); } public boolean keyChar(char arg0, int arg1, int arg2) { // TODO Auto-generated method stub Dialog.alert("key pressed : " + arg0); return true; } public boolean keyDown(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyDown : " + keycode); return false; } public boolean keyRepeat(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyRepeat : " + keycode); return false; } public boolean keyStatus(int keycode, int time) { // TODO Auto-generated method stub Dialog.alert("keyStatus : " + keycode); return false; } public boolean keyUp(int keycode, int time) { Dialog.alert("keyUp : " + keycode); // TODO Auto-generated method stub return false; } } I also tried implementing keyChar on the MainScreen class but that did not yield any results either.

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  • Better way to write this Java code?

    - by Macha
    public void handleParsedCommand(String[] commandArr) { if(commandArr[0].equalsIgnoreCase("message")) { int target = Integer.parseInt(commandArr[1]); String message = commandArr[2]; MachatServer.sendMessage(target, this.conId, message); } else if(commandArr[0].equalsIgnoreCase("quit")) { // Tell the server to disconnect us. MachatServer.disconnect(conId); } else if(commandArr[0].equalsIgnoreCase("confirmconnect")) { // Blah blah and so on for another 10 types of command } else { try { out.write("Unknown: " + commandArr[0] + "\n"); } catch (IOException e) { System.out.println("Failed output warning of unknown command."); } } } I have this part of my server code for handling the types of messages. Each message contains the type in commandArr[0] and the parameters in the rest of commandArr[]. However, this current code, while working seems very unelegant. Is there a better way to handle it? (To the best of my knowledge, String values can't be used in switch statements, and even then, a switch statement would only be a small improvement.

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  • Java: Making concurrent MySQL queries from multiple clients synchronised

    - by Misha Gale
    I work at a gaming cybercafe, and we've got a system here (smartlaunch) which keeps track of game licenses. I've written a program which interfaces with this system (actually, with it's backend MySQL database). The program is meant to be run on a client PC and (1) query the database to select an unused license from the pool available, then (2) mark this license as in use by the client PC. The problem is, I've got a concurrency bug. The program is meant to be launched simultaneously on multiple machines, and when this happens, some machines often try and acquire the same license. I think that this is because steps (1) and (2) are not synchronised, i.e. one program determines that license #5 is available and selects it, but before it can mark #5 as in use another copy of the program on another PC tries to grab that same license. I've tried to solve this problem by using transactions and table locking, but it doesn't seem to make any difference - Am I doing this right? Here follows the code in question: public LicenseKey Acquire() throws SmartLaunchException, SQLException { Connection conn = SmartLaunchDB.getConnection(); int PCID = SmartLaunchDB.getCurrentPCID(); conn.createStatement().execute("LOCK TABLE `licensekeys` WRITE"); String sql = "SELECT * FROM `licensekeys` WHERE `InUseByPC` = 0 AND LicenseSetupID = ? ORDER BY `ID` DESC LIMIT 1"; PreparedStatement statement = conn.prepareStatement(sql); statement.setInt(1, this.id); ResultSet results = statement.executeQuery(); if (results.next()) { int licenseID = results.getInt("ID"); sql = "UPDATE `licensekeys` SET `InUseByPC` = ? WHERE `ID` = ?"; statement = conn.prepareStatement(sql); statement.setInt(1, PCID); statement.setInt(2, licenseID); statement.executeUpdate(); statement.close(); conn.commit(); conn.createStatement().execute("UNLOCK TABLES"); return new LicenseKey(results.getInt("ID"), this, results.getString("LicenseKey"), results.getInt("LicenseKeyType")); } else { throw new SmartLaunchException("All licenses of type " + this.name + "are in use"); } }

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  • some logical error in taking up character in java

    - by Himanshu Aggarwal
    This is my code... class info{ public static void main (String[]args) throws IOException{ char gen; while(true) { //problem occurs with this while System.out.print("\nENTER YOUR GENDER (M/F) : "); gen=(char)System.in.read(); if(gen=='M' || gen=='F' || gen=='m' || gen=='f'){ break; } } System.out.println("\nGENDER = "+gen); } } This is my output... ENTER YOUR GENDER (M/F) : h ENTER YOUR GENDER (M/F) : ENTER YOUR GENDER (M/F) : ENTER YOUR GENDER (M/F) : m GENDER = m Could someone please help me understand why it is asking for the gender so many times.

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  • I have a problem with the following Java code

    - by Sanjeev
    public class b { public static void main(String[] args) { byte b = 1; long l = 127; // b = b + l; // 1 if I try this then it does not compile b += l; // 2 if I try this then it does compile System.out.println(b); } } I am using this code but I have problem: I don't understand why b=b+l; is not compiling but if I write b+=l; then it compiles and runs. Please explain why this happens.

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  • HELP easy java program [closed]

    - by gentrit
    type first integer , type second integer, , program repeatedly outputs the second value of the number of times indicated by the first value. Example use inputs 4 and 2, 222 2 displayed. another example user inputs 3 and 8 , 88 8 displayed

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  • base-n series generator for a given number in java,,

    - by Senthil
    I want to create a program for generating the series for the given base-n. , for example if my input is 2,then series shuould be, 00,01,10,11,etc.,(binary) if my input is 10,then series shuould be,1,2,3,4,5,etc.,(decimal) is there any general mechanism to find these numbers so that I can program for base-n.,

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  • Make a String text Bold in Java Android

    - by meskh
    I want to make Habit Number: bold , I tried the HTML tag but it didn't work. I did some research but couldn't find any. Hope someone is able to help me. Thanks! String habitnumber = "Habit Number: " + String.valueOf(habitcounter); String Title = habit.getTitle(); String description = habit.getDescription(); //Set text for the row tv.setText(habitnumber+ "\n" + Title + " \n" + description + "\n --------------------");

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  • Incorrect Date in Java

    - by Polaris
    I use next code to print current time Calendar cal = Calendar.getInstance(); System.out.println(cal.getTime()); I have Windows XP sp3 istalled. Current time in system tray is 14:30. But this code return 13:30 Why returned time is wrong?

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  • using Inheritence with GUI (graphical user interfaces) in Java

    - by maya
    hi everyone, I work on inheritence with GUI (graphical user interfaces) let me explain for example I made super class which is vehicle and the subclass is car, so the code to make inheritence will be public class Car extends Vehicle then I want to build the class Car as JFrame like public class Car JFrame implements ActionListener { so the problem is that I couldn't put both codes in the same class, and I need to do that. anyone help me. thanks in advance I wish that the question would be clear

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  • How to strip specific contents of a String in Java

    - by user2974877
    So I have a string, and I want to strip out some parts of it using, for example, the firt and last characters of the "interesting" part. String dirty = "$!$!%!%$something interesting&!!$!%$something interesting2"; And the output something like: String clean = "something interesting:something interesting2"; Note: The code needs to work without knowing the random part, changing everytime the program runs. I researched and only found code that does it, but only knowing the random segment.

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  • Check a Date is between two dates in Java

    - by dimitar
    Hello guys, One thing I want to know is how to calculate what date will it be 10 days from today. Second thing is to check if one Date is between two other Dates. For example, let's say I have an app that shows what events I need to do in the next 10 days (planner). Now how can I see if the date I assigned to an event is between today and the date that is 10 days from today?

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