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  • Why people are so afraid of using clone() (on collection and JDK classes) ?

    - by Bozho
    A number of times I've argued that using clone() isn't such a bad practice. Yes, I know the arguments. Bloch said it's bad. He indeed did, but he said that implementing clone() is bad. Using clone on the other hand, especially if it is implemented correctly by a trusted library, such as the JDK, is OK. Just yesterday I had a discussion about an answer of mine that merely suggests that using clone() for ArrayList is OK (and got no upvotes for that reason, I guess). If we look at the @author of ArrayList, we can see a familiar name - Josh Bloch. So clone() on ArrayList (and other collections) is perfectly fine. (Just look at the implementation). Same goes for Calendar and perhaps most of the java.lang and java.util classes. So, give me a reason why not to use clone() with JDK classes?

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  • Issue accessing class variable from thread.

    - by James
    Hello, The code below is meant to take an arraylist of product objects as an input, spun thread for each product(and add the product to the arraylist 'products'), check product image(product.imageURL) availability, remove the products without images(remove the product from the arraylist 'products'), and return an arraylist of products with image available. package com.catgen.thread; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import com.catgen.Product; import com.catgen.Utils; public class ProductFilterThread extends Thread{ private Product product; private List<Product> products = new ArrayList<Product>(); public ProductFilterThread(){ } public ProductFilterThread(Product product){ this.product = product; } public synchronized void addProduct(Product product){ System.out.println("Before add: "+getProducts().size()); getProducts().add(product); System.out.println("After add: "+getProducts().size()); } public synchronized void removeProduct(Product product){ System.out.println("Before rem: "+getProducts().size()); getProducts().remove(product); System.out.println("After rem: "+getProducts().size()); } public synchronized List<Product> getProducts(){ return this.products; } public synchronized void setProducts(List<Product> products){ this.products = products; } public void run(){ boolean imageExists = Utils.fileExists(this.product.ImageURL); if(!imageExists){ System.out.println(this.product.ImageURL); removeProduct(this.product); } } public List<Product> getProductsWithImageOnly(List<Product> products){ ProductFilterThread pft = null; try{ List<ProductFilterThread> threads = new ArrayList<ProductFilterThread>(); for(Product product: products){ pft = new ProductFilterThread(product); addProduct(product); pft.start(); threads.add(pft); } Iterator<ProductFilterThread> threadsIter = threads.iterator(); while(threadsIter.hasNext()){ ProductFilterThread thread = threadsIter.next(); thread.join(); } }catch(Exception e){ e.printStackTrace(); } System.out.println("Total returned products = "+getProducts().size()); return getProducts(); } } Calling statement: displayProducts = new ProductFilterThread().getProductsWithImageOnly(displayProducts); Here, when addProduct(product) is called from within getProductsWithImageOnly(), getProducts() returns the list of products, but that's not the case(no products are returned) when the method removeProduct() is called by a thread, because of which the products without images are never removed. As a result, all the products are returned by the module whether or not the contained products have images. What can be the problem here? Thanks in advance. James.

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  • Using too much memory in C/NDK?

    - by rebeccamaher
    I've recently found out there is no hard limit to how much memory you can allocate in C/NDK on Android. This is in contrast to Java where the limit is ~24Mb. I'm working on a few apps that could greatly benefit from using about ~50Mb total. Is this far too much memory to use? Does anyone have any experience with developing apps that go above the Java limit and what impact this has across devices? Obviously, I don't want to kill all background apps by consuming too much memory and I know the Android devs suggest not using too much memory but limiting all apps to ~24Mb is very limiting to certain kinds of apps. I've seen a few Android games recently that say they use ~256Mb. I'm planning to use about 50Mb total for my app. Does this sound reasonable in terms of stability across devices that have a limit of 24Mb?

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  • due at midnight - program compiles but has logic error(s)

    - by Leslie Laraia
    not sure why this program isn't working. it compiles, but doesn't provide the expected output. the input file is basically just this: Smith 80000 Jones 100000 Scott 75000 Washington 110000 Duffy 125000 Jacobs 67000 Here is the program: import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; /** * * @author Leslie */ public class Election { /** * @param args the command line arguments */ public static void main(String[] args) throws FileNotFoundException { // TODO code application logic here File inputFile = new File("C:\\Users\\Leslie\\Desktop\\votes.txt"); Scanner in = new Scanner(inputFile); int x = 0; String line = ""; Scanner lineScanner = new Scanner(line); line = in.nextLine(); while (in.hasNextLine()) { line = in.nextLine(); x++; } String[] senatorName = new String[x]; int[] votenumber = new int[x]; double[] votepercent = new double[x]; System.out.printf("%44s", "Election Results for State Senator"); System.out.println(); System.out.printf("%-22s", "Candidate"); //Prints the column headings to the screen System.out.printf("%22s", "Votes Received"); System.out.printf("%22s", "%of Total Votes"); int i; for(i=0; i<x; i++) { while(in.hasNextLine()) { line = in.nextLine(); String candidateName = lineScanner.next(); String candidate = candidateName.trim(); senatorName[i] = candidate; int votevalue = lineScanner.nextInt(); votenumber[i] = votevalue; } } votepercent = percentages(votenumber, x); for (i = 0; i < x; i++) { System.out.println(); System.out.printf("%-22s", senatorName[i]); System.out.printf("%22d", votenumber[i]); System.out.printf("%22.2f", votepercent[i]); System.out.println(); } } public static double [] percentages(int[] votenumber, int z) { double [] percentage = new double [z]; double total = 0; for (double element : votenumber) { total = total + element; } for(int i=0; i < votenumber.length; i++) { int y = votenumber[i]; percentage[i] = (y/total) * 100; } return percentage; } }

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  • Singletons and other design issues

    - by Ahmed Saleh
    I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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  • Saving a movie generated with Jython/JES on local disk

    - by Golgauth
    I made an autogenerated movie clip using JES (Jython Environment for Students). I can play it without any problem using playMovie(), but I can't figure out how to have it saved physically on disk. The full script is located here. ... movie = synthesizeFrameAndCreateMovie("D:\\FOLDER") print movie writeQuicktime(movie,"D:\\FOLDER\\movie.mov", 30) [LINE 35] #playMovie(movie) I get this error when calling the function writeQuicktime(): >>> ======= Loading Progam ======= Movie, frames: 60 The error was: Index: 0, Size: 0 I wasn't able to do what you wanted. The error java.lang.IndexOutOfBoundsException has occured Please check line 35 Note : I also tried the function writeAVI(), with the exact same result. This error sounds like a java bug in Jython/JES library. I am running JES under Windows 7 and have all the common Quicktime and AVI codex installed as well as the QTjava library in my jre... Any brilliant idea ? EDIT : Also tried the Linux version with same result for both QuickTime and AVI...

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  • Printing saved HTML to jsp keeps getting corrupted

    - by JWL
    I have a JAVA object where I save a HTML string value I call message. The saved data looks like the below, You have received a new <a href='' onclick='return popupRentalView('5282053859835904');'>Rental Request 5282053859835904</a>. Please view your open orders. But when printed to the JSP file and displayed at runtime using <%=pm.getMessage()%> or <%out.print(pm.getMessage());%> The actual html code comes out all messed up, You have received a new <a 5282053859835904');'="" onclick="return popupRentalView(" href="">Rental Request 5282053859835904</a> . Please view your open orders. Any thoughts on why the displayed string does not match the saved string? JAVA code for saving is note.setMessage("You have received a new <a href=\"\" onclick='return popupRentalView('" + requestId + "');'> Rental Request " + requestId + "</a>. Please view your open orders.");

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  • tuProlog unknow behavior

    - by Josh Guzman
    I'm using tuProlog to integrate Prolog with Java, to do so I'v been defined a .pl file wich contains this code: go:-write('hello world!'),nl. In my Java File at NetBeans i Have a Main Class that invokes this: Prolog engine = new Prolog(); Theory theory = new Theory(new FileInputStream("facultad.pl")); try { engine.setTheory(theory); } catch (InvalidTheoryException ex) { } SolveInfo solution = engine.solve("go."); if (solution.isSuccess()) { System.out.println(solution.getSolution()); } This Code must returns 'hello world', but instead of that it answer 'go', any ideas about this erratic behavior ??

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  • Cnoverting application to MVC architecture

    - by terence6
    I'm practicing writing MVC applications. I have a Mastermind game, that I would like to rewrite as MVC app. I have divided my code to parts, but instead of working game I'm getting empty Frame and an error in "public void paint( Graphics g )". Error comes from calling this method in my view with null argument. But how to overcome this ? MVC was quite simple with swing but awt and it's paint methods are much more complicated. Code of working app : http://paste.pocoo.org/show/224982/ App divided to MVC : Main : public class Main { public static void main(String[] args){ Model model = new Model(); View view = new View("Mastermind", 400, 590, model); Controller controller = new Controller(model, view); view.setVisible(true); } } Controller : import java.awt.*; import java.awt.event.*; public class Controller implements MouseListener, ActionListener { private Model model; private View view; public Controller(Model m, View v){ model = m; view = v; view.addWindowListener( new WindowAdapter(){ public void windowClosing(WindowEvent e){ System.exit(0); } }); view.addMouseListener(this); } public void actionPerformed( ActionEvent e ) { if(e.getSource() == view.checkAnswer){ if(model.isRowFull){ model.check(); } } } public void mousePressed(MouseEvent e) { Point mouse = new Point(); mouse = e.getPoint(); if (model.isPlaying){ if (mouse.x > 350) { int button = 1 + (int)((mouse.y - 32) / 50); if ((button >= 1) && (button <= 5)){ model.fillHole(button); } } } } public void mouseClicked(MouseEvent e) {} public void mouseReleased(MouseEvent e){} public void mouseEntered(MouseEvent e) {} public void mouseExited(MouseEvent e) {} } View : import java.awt.*; import javax.swing.*; import java.awt.event.*; public class View extends Frame implements ActionListener { Model model; JButton checkAnswer; private JPanel button; static final int HIT_X[] = {270,290,310,290,310}, HIT_Y[] = {506,496,496,516,516}; public View(String name, int w, int h, Model m){ model = m; setTitle( name ); setSize( w,h ); setResizable( false ); this.setLayout(new BorderLayout()); button = new JPanel(); button.setSize( new Dimension(400, 100)); button.setVisible(true); checkAnswer = new JButton("Check"); checkAnswer.addActionListener(this); checkAnswer.setSize( new Dimension(200, 30)); button.add( checkAnswer ); this.add( button, BorderLayout.SOUTH); button.setVisible(true); for ( int i=0; i < model.SCORE; i++ ){ for ( int j = 0; j < model.LINE; j++ ){ model.pins[i][j] = new Pin(20,0); model.pins[i][j].setPosition(j*50+30,510-i*50); model.pins[i+model.SCORE][j] = new Pin(8,0); model.pins[i+model.SCORE][j].setPosition(HIT_X[j],HIT_Y[j]-i*50); } } for ( int i=0; i < model.LINE; i++ ){ model.pins[model.OPTIONS][i] = new Pin( 20, i+2 ); model.pins[model.OPTIONS][i].setPosition( 370,i * 50 + 56); } model.combination(); model.paint(null); } public void actionPerformed( ActionEvent e ) { } } Model: import java.awt.*; public class Model extends Frame{ static final int LINE = 5, SCORE = 10, OPTIONS = 20; Pin pins[][] = new Pin[21][LINE]; int combination[] = new int[LINE]; int curPin = 0; int turn = 1; int repaintPin; boolean isUpdate = true, isPlaying = true, isRowFull = false; public Model(){ } void fillHole(int color) { pins[turn-1][curPin].setColor(color+1); repaintPins( turn ); curPin = (curPin+1) % LINE; if (curPin == 0){ isRowFull = true; } } public void paint( Graphics g ) { g.setColor( new Color(238, 238, 238)); g.fillRect( 0,0,400,590); for ( int i=0; i < pins.length; i++ ) { pins[i][0].paint(g); pins[i][1].paint(g); pins[i][2].paint(g); pins[i][3].paint(g); pins[i][4].paint(g); } } public void update( Graphics g ) { if ( isUpdate ) { paint(g); } else { isUpdate = true; pins[repaintPin-1][0].paint(g); pins[repaintPin-1][1].paint(g); pins[repaintPin-1][2].paint(g); pins[repaintPin-1][3].paint(g); pins[repaintPin-1][4].paint(g); } } void repaintPins( int pin ) { repaintPin = pin; isUpdate = false; repaint(); } void check() { int junkPegs[] = new int[LINE], junkCode[] = new int[LINE]; int pegCount = 0, pico = 0; for ( int i = 0; i < LINE; i++ ) { junkPegs[i] = pins[turn-1][i].getColor(); junkCode[i] = combination[i]; } for ( int i = 0; i < LINE; i++ ){ if (junkPegs[i]==junkCode[i]) { pins[turn+SCORE][pegCount].setColor(1); pegCount++; pico++; junkPegs[i] = 98; junkCode[i] = 99; } } for ( int i = 0; i < LINE; i++ ){ for ( int j = 0; j < LINE; j++ ) if (junkPegs[i]==junkCode[j]) { pins[turn+SCORE][pegCount].setColor(2); pegCount++; junkPegs[i] = 98; junkCode[j] = 99; j = LINE; } } repaintPins( turn+SCORE ); if ( pico == LINE ){ isPlaying = false; } else if ( turn >= 10 ){ isPlaying = false; } else{ curPin = 0; isRowFull = false; turn++; } } void combination() { for ( int i = 0; i < LINE; i++ ){ combination[i] = 1 + (int)(Math.random()*5); System.out.print(i+","); } } } class Pin{ private int color, X, Y, radius; private static final Color COLORS[] = { Color.black, Color.white, Color.red, Color.yellow, Color.green, Color.blue, new Color(7, 254, 250)}; public Pin(){ X = 0; Y = 0; radius = 0; color = 0; } public Pin( int r,int c ){ X = 0; Y = 0; radius = r; color = c; } public void paint( Graphics g ){ int x = X-radius; int y = Y-radius; if (color > 0){ g.setColor( COLORS[color]); g.fillOval( x,y,2*radius,2*radius ); } else{ g.setColor( new Color(238, 238, 238) ); g.drawOval( x,y,2*radius-1,2*radius-1 ); } g.setColor( Color.black ); g.drawOval( x,y,2*radius,2*radius ); } public void setPosition( int x,int y ){ this.X = x ; this.Y = y ; } public void setColor( int c ){ color = c; } public int getColor() { return color; } } Any clues on how to overcome this would be great. Have I divided my code improperly ?

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  • Render page as a picture

    - by Sebastian
    I have question to Java or C# programmers. I want to render some pages in various browsers mainly Firefox and IE and save it as a picture. I have not any serious experience in Java/.Net. Is there any libs/tools for such tasks? I thought about some FF extensions for example but I don't know how to do it in IE. Is the in .Net some libs for dealing with it? Maybe some ActiveX? Any sugestions?

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  • Is it acceptable to email an Interviewer after the interview?

    - by djhworld
    Yesterday I took part in an interview for a Java position in a company and one of the questions was Does Java pass by reference or by value? In the heat of the moment I (mistakenly) confidently said it passed by reference, possibly because I come from a C/C++ background. Unfortunately after the interview I'd realised my terrible mistake to my horror. So my question is this, is it acceptable for me to wait a few days and drop a quick email to recognise my mistake? Or should I just let this one lie?

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  • Is there any way to add a MouseListener to a Graphic object ?

    - by Fahad
    Hi, Is there any way to add a MouseListener to a Graphic object. I have this simple GUI that draw an oval. What I want is handling the event when the user clicks on the oval import java.awt.*; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import javax.swing.*; public class Gui2 extends JFrame { JFrame frame = new JFrame(); MyDrawPanel drawpanel = new MyDrawPanel(); public static void main(String[] args) { Gui2 gui = new Gui2(); gui.go(); } public void go() { frame.getContentPane().add(drawpanel); // frame.addMouseListener(this); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(300, 300); frame.setVisible(true); } } class MyDrawPanel extends JComponent implements MouseListener { public void paintComponent(Graphics g) { int red = (int) (Math.random() * 255); int green = (int) (Math.random() * 255); int blue = (int) (Math.random() * 255); Color startrandomColor = new Color(red, green, blue); red = (int) (Math.random() * 255); green = (int) (Math.random() * 255); blue = (int) (Math.random() * 255); Color endrandomColor = new Color(red, green, blue); Graphics2D g2d = (Graphics2D) g; this.addMouseListener(this); GradientPaint gradient = new GradientPaint(70, 70, startrandomColor, 150, 150, endrandomColor); g2d.setPaint(gradient); g2d.fillOval(70, 70, 100, 100); } @Override public void mouseClicked(MouseEvent e) { if ((e.getButton() == 1) && (e.getX() >= 70 && e.getX() <= 170 && e.getY() >= 70 && e .getY() <= 170)) { this.repaint(); // JOptionPane.showMessageDialog(null,e.getX()+ "\n" + e.getY()); } } @Override public void mouseEntered(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseExited(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mousePressed(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseReleased(MouseEvent e) { // TODO Auto-generated method stub } } This Works Except it fires when the click is within a virtual box around the oval. Could anyone help me to have it fire when the click is EXACTLY on the oval. Thanks in advance.

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  • Eclipse: Double semi-colon on an import

    - by smp7d
    Using Eclipse, if I have an extra semicolon on an import line (not the last import line), I see a syntax error in the IDE. However, this compiles fine outside of the IDE (Maven in this case). Example: import java.util.ArrayList;; //notice extra semicolon import java.util.List; Does anyone else see this behavior? Why is this showing as a syntax error? I am working with someone who keeps pushing these this to source control and it is irritating me (they clearly aren't using Eclipse). Full disclosure... I am using SpringSource Tool Suite 2.8.0.

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  • how to store passwords in database?

    - by rgksugan
    I use jsp and servlets in my web application. i need to store passwords in the database. I found that hashing will be the best way to do that. I used this code to do it. java.security.MessageDigest d = null; d = java.security.MessageDigest.getInstance("SHA-1"); d.reset(); d.update(pass.getBytes("UTF-8")); byte b[] = d.digest(); String tmp = (new BASE64Encoder()).encode(b); When i tried to print the value of tmp, i get some other value.i guess its the hash value of the password. But when i persist this data to the database the original password gets saved there other than the value in tmp.. What is the problem???

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  • FlashBuilder4 RIA on GAE

    - by user330195
    I've read/watched most of your blog/tuts and it seems you are the "beautiful front-ends for Java based back-ends" guru ;) That (sucking up ;) said, I want to build a highly scalable "facebook for business" and after much testing am pretty set on FlashBuilder4 (Flex) with Google App Engine (GAE). What are your thoughts on the need/advisability of also using Spring/Cairngorm/etc frameworks? Frankly I don't have extensive experience coding, however feel the "MVC utopia" universally aspired to becomes convoluting when duplicating between front and back ends as envisioned above (i.e. Flex/ActionScript and GAE/Java respectively).

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  • Are there any OSGi web service / SOAP clients out there?

    - by James Carr
    I'm looking for any webservice client that can be run inside an OSGi container and connect to a simple web service using SOAP, doesn't sound so hard does it? Oh, and it has to work under Java 1.5, so the JRE jax-ws wont be present. The problem is I've tried a few solutions now, and although each solution works in standard Java using it from within OSGi doesn't. the springsource JAX-WS bundles seem to have dependency issues the CXF bundles get me as far as calling the service, but then can seem to find the stub methods in the proxy Is there anyone out there who has successfully created an OSGi webservice client?

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  • Why is Scala very complex?

    - by Anantha Kumaran
    I am a student. I learned java during the 2nd year. Now i am in fourth year. I got bored with java and i started to learn Scala. As i learn it, i found it being very complex (although i love it). My question may apply to all new complex language. Why scala is complex? is it because we need to create complex softwares? or i am the only one who thinks it is complex?

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  • How can I avoid mutable variables in Scala when using ZipInputStreams and ZipOutpuStreams?

    - by pr1001
    I'm trying to read a zip file, check that it has some required files, and then write all valid files out to another zip file. The basic introduction to java.util.zip has a lot of Java-isms and I'd love to make my code more Scala-native. Specifically, I'd like to avoid the use of vars. Here's what I have: val fos = new FileOutputStream("new.zip"); val zipOut = new ZipOutputStream(new BufferedOutputStream(fos)); while (zipIn.available == 1) { val entry = zipIn.getNextEntry if (entryIsValid(entry)) { val fos = new FileOutputStream("subdir/" + entry.getName()); val dest = new BufferedOutputStream(fos); // read data into the data Array var data: Array[Byte] = null var count = zip.read(data) while (count != -1) { dest.write(data, 0, count) count = zip.read(data) } dest.flush dest.close } }

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  • Sending an email when an Exception is Thrown

    - by hariubc
    Hi: I have written a java class where if a method throws an exception, an email is sent, via java mail, with a report to the administrators. It works - my question is w.r.t elegance - to catch the exception thrown by the main method, the sendEmail() method resides in the catch block of the main method. The sendEmail() method has its own try-catch block. In effect - it looks like below - is there a more beautiful way of writing this? try { foo; } catch { try{ sendEmail(); } catch { log(e.message); } }

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  • Package <blah> does not exist error - NetBeans 6.8 & Windows 7

    - by BenMc
    I'm using NetBeans 6.8 on Windows 7. I upgraded from WinXP and NetBeans 6.7. Now my existing java web app project is no longer able to import/find the packages I've developed - I receive a 'Package ,blah. does not exist' and yet the packages do exist, worked fine in NetBeans 6.7 and the project still compiles and runs OK. I've tried changing the Java Platform/JDK from 1.6.0_10 back to JDK 1.5.0_22 but I still receive errors package does not exist. All other 'standard' libraries and packages are able to be imported and used OK ... eg Struts, Hibernate

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