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  • Java 7 API design best practice - return Array or return Collection

    - by Shengjie
    I know this question has be asked before generic comes out. Array does win out a bit given Array enforces the return type, it's more type-safe. But now, with latest JDK 7, every time when I design this type of APIs: public String[] getElements(String type) vs public List<String> getElements(String type) I am always struggling to think of some good reasons to return A Collection over An Array or another way around. What's the best practice when it comes to the case of choosing String[] or List as the API's return type? Or it's courses for horses. I don't have a special case in my mind, I am more looking for a generic pros/cons comparison.

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  • Java: Generating distribution of values in an ArrayList

    - by Matt
    Hi all, I have a sorted ArrayList of values. I would like to get the distribution of the values. For example: Say I have 500 values, ranging from 1-100. I want to break them up into groups, say 10 groups: values 1-10, 11-20, 21-30, etc... I want the counts of each of the 500 values that fall into each category. For example, 5 of the 500 are valued at 1-10, 20 between 11-20, etc... However, I do not know the ranges of values in my ArrayList, it could be ranging from 1-30 or 1-200, but I want to break it up into, for example, 10 groups. Does anyone know how to do this?

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  • Java Simple ActionListener Questions

    - by Allen
    I have a main class in a program that launches another class that handles all the GUI stuff. In the GUI, i have a button that i need to attach an ActionListener to. The only problem is, the code to be executed needs to reside within the main class. How can i get the ActionPerformed() method to execute in the main class when a button is clicked elsewhere?

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  • Java BufferedReader behavior in CSV vs TXT file

    - by Gabriel
    If i try to read a CSV file called csv_file.csv. The problem is that when i read lines with BufferedReader.readLine() it skips the first line with months. But when i rename the file to csv_file.txt it reads it allright and it's not skipping the first line. Is there an undocumented "feature" of BufferedReader that i'm not aware? Example of file: Months, SEP2010, OCT2010, NOV2010 col1, col2, col3, col4, col5 aaa,,sdf,"12,456",bla bla bla, xsaffadfafda and so on, and so on, "10,00", xxx, xxx The code: FileInputStream stream = new FileInputStream(UploadSupport.TEMPORARY_FILES_PATH+fileName); BufferedReader br = new BufferedReader(new InputStreamReader(stream, "UTF-8")); String line = br.readLine(); String months[] = line.split(","); while ((line=br.readLine())!=null) { /*parse other lines*/ }

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  • I have problem using vesijama (Very Simple Java Mail)

    - by Huuhaacece
    Hi, i already read this tutorial from here and i have download all required libraries (Log4j, JavaMail API ,Activation framework) . But when i trying running this program i got this error log4j:WARN No appenders could be found for logger (org.codemonkey.vesijama.Mailer). org.codemonkey.vesijama.MailException: Generic error: Exception reading response log4j:WARN Please initialize the log4j system properly. this is the source code i use import javax.mail.Message.RecipientType; import org.codemonkey.vesijama.Email; import org.codemonkey.vesijama.MailException; import org.codemonkey.vesijama.Mailer; public class testSend { final Email email = new Email(); public testSend{ try{ email.setFromAddress("test", "[email protected]"); email.setSubject("hey"); email.addRecipient("hai", "[email protected]", RecipientType.TO); email.setText("We should meet up!"); email.setTextHTML("<b>We should meet up!</b>"); new Mailer("smtp.gmail.com", 465, "[email protected]", "XXXXXX").sendMail(email); } catch(MailException me) { System.out.println(me); } } } i have also trying using port 587. but i got same error .< btw , it say can add attachments what should i write if i want to attach .xls ( microsoft excel 2003) ? Thx B4.

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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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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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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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  • Java Stopping JApplet Components from Resizing based on Applet Size

    - by Doug
    Creating a JApplet I have 2 Text Fields, a button and a Text Area. private JPanel addressEntryPanel = new JPanel(new GridLayout(1,3)); private JPanel outputPanel = new JPanel(new GridLayout(1,1)); private JTextField serverTf = new JTextField(""); private JTextField pageTf = new JTextField(""); private JTextArea outputTa = new JTextArea(); private JButton connectBt = new JButton("Connect"); private JScrollPane outputSp = new JScrollPane(outputTa); public void init() { setSize(500,500); setLayout(new GridLayout(3,1)); add(addressEntryPanel); addressEntryPanel.add(serverTf); addressEntryPanel.add(pageTf); addressEntryPanel.add(connectBt); addressEntryPanel.setPreferredSize(new Dimension(50,50)); addressEntryPanel.setMaximumSize(addressEntryPanel.getPreferredSize()); addressEntryPanel.setMinimumSize(addressEntryPanel.getPreferredSize()); add(outputPanel); outputPanel.add(outputSp); outputTa.setLineWrap(true); connectBt.addActionListener(this); The problem is when debugging and putting it in a page the components / panels resize depending on the applet size. I don't want this. I want the textfields to be a certain size, and the text area to be a certain size. I've put stuff in there to set the size of them but they aren't working. How do I go about actually setting a strict size for either the components or the JPanel.

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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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  • Java: how to read BufferedReader faster

    - by Cata
    Hello, I want to optimize this code: InputStream is = rp.getEntity().getContent(); BufferedReader reader = new BufferedReader(new InputStreamReader(is)); String text = ""; String aux = ""; while ((aux = reader.readLine()) != null) { text += aux; } The thing is that i don't know how to read the content of the bufferedreader and copy it in a String faster than what I have above. I need to spend as little time as possible. Thank you

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  • Java iText Image position

    - by skowron-line
    I have: Image i = Image.getInstance("tabelka.png"); i.scalePercent(25, 25); for(int i=0; i<= 5; i++) { doc.add(i); content.moveTo(50, ??);////// <-------------- HOW TO CHECK THE Y POSITION content.showText("skowron-line"); } I want to set text on upper right corner of image. How do I do that? EIDT: After hours of thinkin i found dirty solution: Image img = Image.getInstance("tabelka.png"); img.scalePercent(25, 25); float start = x; for(int i =1; i<= 5; i++) { start = (x - (img.getHeight() * 0.25f) * i); } If U know better solution let me know.

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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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  • synchronized in java - Proper use

    - by ZoharYosef
    I'm building a simple program to use in multi processes (Threads). My question is more to understand - when I have to use a reserved word synchronized? Do I need to use this word in any method that affects the bone variables? I know I can put it on any method that is not static, but I want to understand more. thank you! here is the code: public class Container { // *** data members *** public static final int INIT_SIZE=10; // the first (init) size of the set. public static final int RESCALE=10; // the re-scale factor of this set. private int _sp=0; public Object[] _data; /************ Constructors ************/ public Container(){ _sp=0; _data = new Object[INIT_SIZE]; } public Container(Container other) { // copy constructor this(); for(int i=0;i<other.size();i++) this.add(other.at(i)); } /** return true is this collection is empty, else return false. */ public synchronized boolean isEmpty() {return _sp==0;} /** add an Object to this set */ public synchronized void add (Object p){ if (_sp==_data.length) rescale(RESCALE); _data[_sp] = p; // shellow copy semantic. _sp++; } /** returns the actual amount of Objects contained in this collection */ public synchronized int size() {return _sp;} /** returns true if this container contains an element which is equals to ob */ public synchronized boolean isMember(Object ob) { return get(ob)!=-1; } /** return the index of the first object which equals ob, if none returns -1 */ public synchronized int get(Object ob) { int ans=-1; for(int i=0;i<size();i=i+1) if(at(i).equals(ob)) return i; return ans; } /** returns the element located at the ind place in this container (null if out of range) */ public synchronized Object at(int p){ if (p>=0 && p<size()) return _data[p]; else return null; }

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  • java thread - run() and start() methods

    - by JavaUser
    Please explain the output of the below code: If I call th1.run() ,the output is EXTENDS RUN RUNNABLE RUN If I call th1.start() , the output is : RUNNABLE RUN EXTENDS RUN Why this inconsistency . Please explain. class ThreadExample extends Thread{ public void run(){ System.out.println("EXTENDS RUN"); } } class ThreadExampleRunnable implements Runnable { public void run(){ System.out.println("RUNNABLE RUN "); } } class ThreadExampleMain{ public static void main(String[] args){ ThreadExample th1 = new ThreadExample(); //th1.start(); th1.run(); ThreadExampleRunnable th2 = new ThreadExampleRunnable(); th2.run(); } }

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  • How to copy .java sources to Ant javac destFolder

    - by Ittai
    Hi, I know how to use Ant to copy files and folders but what I'm interested in is if, and how, I can have the javac task copy the same sources it's compiling to the output directory. Basically, it's very similar to the option to include your sources in the jar task. Thanks in advance, Ittai

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  • java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

    - by Jason S
    I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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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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  • using itext how to extracta string in java

    - by user2455183
    I am finding the string in between 123 and 321 and making it as bold. For that I used the Pattern to get the string before 123, text between 123 and 321 and text after 321. Could anyone please help me get all the strings between 123 and 321. Pattern p = Pattern.compile("^.*?(123)"); Matcher m = p.matcher(meredithEditorialSectionSegment); while (m.find()) { String desc = m.group(); String segDesc = (desc.substring(0, desc.length() - 3)); segmentDesc.add(new Chunk(segDesc, sectionDescriptionFont)); } descBold = meredithEditorialSectionSegment.substring(meredithEditorialSectionSegment.indexOf("123") + 3); descBold = descBold.substring(0, descBold.indexOf("321")); segmentDesc.add(new Chunk(descBold, sectionDescriptionBoldFont)); Matcher matcher = Pattern.compile("(?<=321).*").matcher(meredithEditorialSectionSegment); matcher.find(); segmentDesc.add(new Chunk(matcher.group(), sectionDescriptionFont));

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  • Java do while, while

    - by Pindatjuh
    Hello, what behaviour can I expect when I run this code: do while(testA) { // do stuff } while(testB); Will it behave like: do { while(testA) { // do stuff } } while(testB); Or: if(testA) { do { // do stuff } while(testA && testB); } Or something totally unexpected? I ask this question because I think this is quite ambiguous, and for other people searching on this topic, not because I am lazy to test it out.

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  • Formatting a byte array to string in java

    - by rgksugan
    I am using this code to find the MAC address of a machine.This code prints directly the MAC address, but i want to return it as a string.I am completely confused. please help. try { InetAddress add = InetAddress.getByName("10.123.96.102"); NetworkInterface ni1 = NetworkInterface.getByInetAddress(add); if (ni1 != null) { byte[] mac1 = ni1.getHardwareAddress(); if (mac1 != null) { for (int k = 0; k < mac1.length; k++) { System.out.format("%02X%s", mac1[k], (k < mac1.length - 1) ? "-" : ""); } } else { System.out.println("Address doesn't exist "); } System.out.println(); } else { System.out.println("address is not found."); } } catch (UnknownHostException e) { e.printStackTrace(); } catch (SocketException e) { e.printStackTrace(); }

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