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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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• Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

  - by mihi

  Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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• Sending an Email Using Java

  - by user217029

  try{ Properties props = new Properties(); props.put("mail.smtp.host", "ipc-smtp.bits-pilani.ac.in"); Session sess = Session.getInstance(props, null); sess.setDebug(true); Message msg = new MimeMessage(sess); InternetAddress addressFrom = new InternetAddress("[email protected]"); msg.setFrom(addressFrom); msg.setRecipient(Message.RecipientType.TO, new InternetAddress("[email protected]")); msg.addHeader("MyHeaderName", "myHeaderValue"); msg.setSubject("Test"); msg.setContent("Yippe", "text/plain"); Transport.send(msg); }catch(Exception exp){ exp.printStackTrace(); } The error is javax.mail.MessagingException: 554 The mail was blocked due to zen-spamhaus RBL action This is my college's smtp server.

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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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• Math operation in Java

  - by joroj

  Hello, what "^" operator does? when I try this: int a = 5^n; it gives me: for n = 5, returns 0 for n = 4, returns 1 for n = 6, returns 3 What is this?

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• Date conversion in Java

  - by llm

  How can I take a string in a format such as: 2008-06-02 00:00:00.0 and convert it to: 02-Jun-2008? Can I somehow take the original string, convert it to a Date object, then use a formatter to get the final output (rather than parsing the string myself)? Thanks!

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• Read / Write XML file from Java application bundle

  - by Peter

  Hi there! I've got an XML file that is parsed and written in my application. From within my IDE (Eclipse) I simply address it like this: Reading: private String xmlFile = "file.xml"; and then I build the document: doc = sax.build(xmlFile); Writing is done like this: writer = new FileWriter("file.xml"); Runs great so far, but after bundling my application, the file is no longer accessible. What exactly do I have to do to make it accessible from within an application bundle? I'm absolutely not familiar with the classpath or whatever I need for that, so please go easy on me! Thank you very much!

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• How to show tabular data in a Java web app

  - by arahant7

  Is there any counterpart to ASP.NET's DataGrid (or DataView) in the various J2EE web application technologies (specifically Struts)? In other words, what is the de facto method for showing tabular data in a J2EE web application?

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• Java Data Structure

  - by Joe

  Hi there, I'm looking for a data structure that will act like a Queue so that I can hava First In First Out behaviour, but ideally I would also be able to see if an element exists in that Queue in constant time as you can do with a HashMap, rather than the linear time that you get with a LinkedList. I thought a LinkedHashMap might do the job, but although I could make an iterator and just take and then remove the first element of the iteration to produce a sort of poll() method, I'm wondering if there is a better way. Many thanks in advance

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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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• Need help in Architecture design in java

  - by palakolanusrinu

  Can anyone help in architecture design of one of my complex application. Requirement : In web based application, we need to generate Excel kind of report as HTML page and after that we need to perform different kinds of operations like Add manual rows Delete rows Edit rows adding comments based on each cell viewing the added comments. attaching the file based on each cell viewing the attached file. Collapsible functionality for some of rows In the process of design we have come up with DB design and application framework is Spring. and for Web not yet finalized. what is the best approach to implement this kind of UI? --JSF?(keep in mind we need to Excel operations like above mentioned operations) -- Any reporting tool which will provide editing functionality? Please suggest me How can we do it? and what is the best technology for it? or is there any reporting tools?

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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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• List files with two dots in their names using java regular expressions

  - by Nivas

  I was trying to match files in a directory that had two dots in their name, something like theme.default.properties I thought the pattern .\\..\\.. should be the required pattern [. matches any character and \. matches a dot] but it matches both oneTwo.txt and theme.default.properties I tried the following: [resources/themes has two files oneTwo.txt and theme.default.properties] 1. public static void loadThemes() { File themeDirectory = new File("resources/themes"); if(themeDirectory.exists()) { File[] themeFiles = themeDirectory.listFiles(); for(File themeFile : themeFiles) { if(themeFile.getName().matches(".\\..\\..")); { System.out.println(themeFile.getName()); } } } } This prints nothing and the following File[] themeFiles = themeDirectory.listFiles(new FilenameFilter() { public boolean accept(File dir, String name) { return name.matches(".\\..\\.."); } }); for (File file : themeFiles) { System.out.println(file.getName()); } prints both oneTwo.txt theme.default.properties I am unable to find why these two give different results and which pattern I should be using to match two dots... Can someone help?

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• Java regex replace multiple file paths in a large String

  - by Joe Goble

  So a Regex pro I am not, and I'm looking for a good way to do this. I have a large string which contains a variable number <img> tags. I need to change the path on all of these images to images/. The large string also contains other stuff not just these img's. <img src='http://server.com/stuff1/img1.jpg' /> <img src='http://server.com/stuff2/img2.png' /> Replacing the server name with a ReplaceAll() I could do, it's the variable path in the middle I'm clueless on how to include. It doesn't necessarily need to be a regex, but looping through the entire string just seems wasteful.

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• Does Java have a .new operator?

  - by chickeninabiscuit

  I came across this code today whilst reading Accelerated GWT (Gupta) - page 151. public static void getListOfBooks(String category, BookStore bookStore) { serviceInstance.getBooks(category, bookStore.new BookListUpdaterCallback()); } public static void storeOrder(List books, String userName, BookStore bookStore) { serviceInstance.storeOrder(books, userName, bookStore.new StoreOrderCallback()); } What are those new operators doing there? I've never seen such syntax, can anyone explain?

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• Require a default constructor in java?

  - by jdc0589

  Is there any way to require that a class have a default (no parameter) constructor, aside from using a reflection check like the following? (the following would work, but it's hacky and reflection is slow) boolean valid = false; for(Constructor<?> c : TParse.class.getConstructors()) { if(c.getParameterTypes().length == 0) { valid = true; break; } } if(!valid) throw new MissingDefaultConstructorException(...);

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• Read / write program in java using JChooser

  - by Casper Marcussen

  Hello everyone Didn't want to bother people in here, but since i am under a time pressure, i am desperate to get help. My questions is how to link the file choosen from a JChooser to a file, and how to converte it to stringm being able to display and edit it in a TextArea. i hav ethe GUI set up using swing, but the link between actionListener and the Jchooser is not complete Any help would be much appreciated code: http://pastebin.com/p3fb17Wi

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• Java Swing custom shapes (2D Graphics)

  - by juFo

  I need to draw custom shapes. Now when a user clicks on several points on the panel I create a shape using a polygon. public void mouseClicked(MouseEvent e) { polygon.addPoint(e.getX(), e.getY()); repaint(); } But I don't know if this is the best way to draw custom shapes. It should be possible to edit a drawn shape: resize change its fill color change the stroke color copy/paste it move a single point of the polygon ... I have seen people creating an own class implementing the Shape class and using a GeneralPath. But again I have no idea if this is a good way. Now I can create my own shape with a polygon (or with a GeneralPath) but I have no clue how to attach all the edit functions to my own shape (the edit functions I mean the resize, move, etc from above). I hope somebody could show me a way to do this or maybe write a little bit of code to demonstrate this. Thanks in advance!!

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• Polling servers at the same port - Threads and Java

  - by John

  Hi there. I'm currently busy working on an IP ban tool for the early versions of Call of Duty 1. (Apparently such a feature wasn't implemented in these versions). I've finished a single threaded application but it won't perform well enough for multiple servers, which is why I am trying to implement threading. Right now, each server has its own thread. I have a Networking class, which has a method; "GetStatus" -- this method is synchronized. This method uses a DatagramSocket to communicate with the server. Since this method is static and synchronized, I shouldn't get in trouble and receive a whole bunch of "Address already in use" exceptions. However, I have a second method named "SendMessage". This method is supposed to send a message to the server. How can I make sure "SendMessage" cannot be invoked when there's already a thread running in "GetStatus", and the other way around? If I make both synchronized, I will still get in trouble if Thread A is opening a socket on Port 99999 and invoking "SendMessage" while Thread B is opening a socket on the same port and invoking "GetStatus"? (Game servers are usually hosted on the same ports) I guess what I am really after is a way to make an entire class synchronized, so that only one method can be invoked and run at a time by a single thread. Hope that what I am trying to accomplish/avoid is made clear in this text. Any help is greatly appreciated.

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• What's wrong with my logic (Java syntax)

  - by soda

  I'm trying to make a simple program that picks a random number and takes input from the user. The program should tell the user if the guess was hot (-/+ 5 units) or cold, but I never reach the else condition. Here's the section of code: public static void giveHint (int guess) { int min = guess - 5; int max = guess + 5; if ((guess > min) && (guess < max)) { System.out.println("Hot.."); } else { System.out.println("Cold.."); } }

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• Java OS X - No app icon in dock

  - by Jacob

  I am using Jar Bundler to create a .app file out of my .jar file. When I launch the app, I do not want a dock icon to show at all. I have already tried modifying my .plist file to include: <string>NSUIElement</string> <key>1</key> But it does not work... Any help?

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• HQL make query searching by date (Java+NetBeans)

  - by Zloy Smiertniy

  Hi all I have the following issue. I have a table of reserves in my MySQL DB, the date columns is defined DATETIME. I need to make a query using hibernate to find all reserves in one day no matter the hour, just that its the same year month and date, and I'm doing this public List<Reserve> bringAllResByDate(Date date){ em = emf.createEntityManager(); Query q = em.createQuery("SELECT r FROM Reserve r WHERE r.date=:date "); q.setParameter("date", date); ... I really dont know how to make it compare, and bring me just those from the specified date, any help??

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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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• Trying to convert a 2D image into 3D objects in Java

  - by Kyle

  Hey, I'm trying to take a simple image, something like a black background with colored blocks representing walls. I'm trying to figure out how to go about starting on something like this. Do I need to parse the image and look at each pixel or is there an easier way to do it? I'm using Java3D but it doesn't seem to have any sort of built in support for that...

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• java mail service

  - by merin

  is it possible to send newsletter from my site to my clients yahoo,rediff mail accounts

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