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• are custom classes imported API included in .class files?

  - by kyrogue

  i have a question, i have a custom class which imports java.sql.; and i am creating a jsp page, in the jsp page, i did a page import of the custom class , however when i tried to call my custom class database methods it cant work. only when i did a page import of java.sql. did it work. so are custom classes imported API included in .class files? An error occurred at line: 6 in the jsp file: /resetpw.jsp Statement cannot be resolved to a type 3: 4: <% 5: db.connect(); 6: Statement stmt = db.getConnection().createStatement(); 7: ResultSet rs = stmt.executeQuery("SELECT * FROM created_accounts"); 8: 9: An error occurred at line: 7 in the jsp file: /resetpw.jsp ResultSet cannot be resolved to a type 4: <% 5: db.connect(); 6: Statement stmt = db.getConnection().createStatement(); 7: ResultSet rs = stmt.executeQuery("SELECT * FROM created_accounts"); 8: 9: 10: Stacktrace: org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:93) org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:330) org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:451) org.apache.jasper.compiler.Compiler.compile(Compiler.java:319) org.apache.jasper.compiler.Compiler.compile(Compiler.java:298) org.apache.jasper.compiler.Compiler.compile(Compiler.java:286) org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:565) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:309) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:308) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:259) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) note The full stack trace of the root cause is available in the Apache Tomcat/5.5.31 logs. edited. added what error will come up if i did not do a page import of java.sql.*;

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• java gregorian calendar timer

  - by Ieyasu Sawada

  I have this java program which calculates the time that the person took to respond to the confirm dialog box. But it seems that both time1 and time 2 gets the same value. What have I done wrong here: import javax.swing.JOptionPane; import java.util.*; public class DialogTimer{ public static void main(String args[]){ int time1, time2, milli1, milli2, sec1, sec2, timeDifference; final int MILLISECSINSECOND =1000; JOptionPane.showConfirmDialog(null, "Is stealing ever justified? "); GregorianCalendar before=new GregorianCalendar(); GregorianCalendar after= new GregorianCalendar(); milli1=before.get(GregorianCalendar.MILLISECOND); milli2=after.get(GregorianCalendar.MILLISECOND); sec1=before.get(GregorianCalendar.SECOND); sec2=after.get(GregorianCalendar.SECOND); time1=MILLISECSINSECOND * sec1 + milli1; time2=MILLISECSINSECOND * sec2 + milli2; //timeDifference=time1 - time2; System.out.println(time1); System.out.println(time2); //JOptionPane.showMessageDialog(null, "It took " + (time1 - time2) + " milliseconds for you to answer"); } }

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• Desktop-like UI implementations for Java web applications?

  - by localshred

  At work we're discussing upgrading our view layer for our web application. We're currently running an old and "modified" version of FreeMarker Classic, which is a pain to work with. One of our developers suggested using a Component UI style architecture similar to desktop style environments. Essentially, this would mean that you would build custom HTML components as Java Classes that the controller would render into the Document view. This would completely take away the need to write HTML into a view layer. The Components would generate the view layer for you. For instance, the following rendered HTML: <h1>I am a title</h1> <p>I am a paragraph.</p> Would be generated by doing something like: String titleString = "I am a title"; html.elements.Heading heading = new html.elements.Heading(Heading.H1, titleString); String paraString = "I am a paragraph."; html.elements.Paragraph paragraph = new html.elements.Paragraph(paraString); PrintWriter somePrintWriter = new PrintWriter(); Document document = new Document(); document.addElement(heading); document.addElement(paragraph); document.compose(somePrintWriter); The above code is just an example, don't critique the names or style, I just wrote it for a quick demonstration of what we may be trying to accomplish. I'm trying to determine if this has been done before in Java, and if so if there are any links I can be pointed to. I've been researching it as much as I can, but haven't found any implementations that completely remove the template layer (such as JSP or JSF). Thanks!

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• Java Formatter specify starting position for text

  - by purecharger

  I'm trying to position a string at a certain starting position on a line, regardless of where the previous text ended. For instance: Mandatory arguments to long options are mandatory for short options too. -a, --all do not ignore entries starting with . -A, --almost-all do not list implied . and .. The explanation of the options begin at position 30 regardless of the text preceding. How do you accomplish this with java.util.Formatter? I have tested with both the width (%30s) and precision (%.30) arguments, and neither provide the desired result.

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• How do I create a hyperlink in java?

  - by Justin984

  I'm going through the google app engine tutorials at https://developers.google.com/appengine/docs/java/gettingstarted/usingusers I'm very new to google app engine, java and web programming in general. So my question is, at the bottom of the page it says to add a link to allow the user to log out. So far I've got this: public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); if(user != null){ resp.setContentType("text/plain"); resp.getWriter().println("Hello, " + user.getNickname()); String logoutLink = String.format("<a href=\"%s\">Click here to log out.</a>", userService.createLogoutURL(req.getRequestURI())); resp.getWriter().println(logoutLink); }else { resp.sendRedirect(userService.createLoginURL(req.getRequestURI())); } } However instead of a link, the full string is printed to the screen including the tags. When I look at the page source, I have no tags or any of the other stuff that goes with a webpage. I guess that makes sense considering I've done nothing to output any of that. Do I just do a bunch of resp.GetWriter().println() statements to output the rest of the webpage, or is there something else I don't know about? Thanks!

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• Java Function Analysis

  - by khan

  Okay..I am a total Python guy and have very rarely worked with Java and its methods. The condition is that I have a got a Java function that I have to explain to my instructor and I have got no clue about how to do so..so if one of you can read this properly, kindly help me out in breaking it down and explaining it. Also, i need to find out any flaw in its operation (i.e. usage of loops, etc.) if there is any. Finally, what is the difference between 'string' and 'string[]' types? public static void search(String findfrom, String[] thething){ if(thething.length > 5){ System.err.println("The thing is quite long"); } else{ int[] rescount = new int[thething.length]; for(int i = 0; i < thething.length; i++){ String[] characs = findfrom.split("[ \"\'\t\n\b\f\r]", 0); for(int j = 0; j < characs.length; j++){ if(characs[j].compareTo(thething[i]) == 0){ rescount[i]++; } } } for (int j = 0; j < thething.length; j++) { System.out.println(thething[j] + ": " + rescount[j]); } } }

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• Returning the index number of an Arraylist in Java

  - by Daniel

  I would like my method public void showClassRoomDetails(String teacherName) to return the Arraylist index number using the teacherName. Thanks import java.util.ArrayList; public class School { private ArrayList<Classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<Classroom>(); } public void addClassRoom(Classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } public void addTeacherToClassRoom(int classroomId, String TeacherName) { if (classroomId < classrooms.size() ) { classrooms.get(classroomId).setTeacherName(TeacherName); } } public void showClassRoomDetails(String teacherName) { for (Classroom classroom : this.classrooms) { if (classroom.returnTeacherName().equals(teacherName)) { System.out.println(classroom.returnClassRoomName()); System.out.println(classroom.returnTeacherName()); break; } } } }

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• How to set specific column settings in JTable?

  - by HansDampf

  How can I make my JTable show specific stuff for each column? Can I use an Object for more than one column? I want to have a column showing the date (dd.mm.yyyy) and another to show the time (hh:mm) but as I have it now it only shows the String representation of the Date object as a whole. public class AppointmentTableModel extends AbstractTableModel { ... @Override public Object getValueAt(int rowIndex, int columnIndex) { return appointments.get(rowIndex).getByColumn(columnIndex); } } public class Appointment { ... public Object getByColumn(int columnIndex) { switch (columnIndex) { case 0: return date; case 1: return date; case 2: return sample; case 3: return sample; case 4: return history; case 5: return comment; } return null; } }

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• Rendering maps from raw SVG data in Java

  - by Lunikon

  In an application of mine I have to display locations and great circle paths in a map which is rendered to PNG and then displayed on the web. For this I simply use a world map (NASA's Blue Marbel in fact) scaled to various "zoom levels" as base image and only display the a part of it matching the final image size and fitting all items to be displayed. Straight forward so far. Now I came across Wikipedia's awesome blank SVG maps which contain all the country codes for easy reference and I was wondering whether it was possible to use those to have more customized colors and to highliht countries etc. So I did a bit of googling and was looking for Java libraries which would enable me to load the blank SVG map to memory allows for easy reference/selection of certain paths do manipulations of coloring, stroke widths etc render to a buffered image as the background for the great-circle paths/nodes What I came across quite often was Batik, but it looks like a really heavy framework and I'm not quite sure whether it is what I'm looking for. I have recently played around with Raphaël a bit and I like the way it handles working with vector graphics in code. If the Java framework for my purpose would feature a similar interface, that would be a nice-to-have. Any recommendations what toolset would be approriate for my purposes?

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• What to call factory-like (java) methods used with immutable objects

  - by StaxMan

  When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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• Blackberry (Java) - Setting scrolling be not focused on objects on the screen

  - by paullb

  I have a mainscreen which currently scrolls (and I have the arrows on the right) but the scrolling seems to be focused on the ButtonField objects that I have on the page. Is there any way to set the scrolling to be non-focused scrolling (moving a few pixels each time). Is there a way to set this? Other ideas I have had (which sound hacky so I want to avoid): - Placing NullFields around to scroll - Manually listening to the trackwheelRoll event and moving appropriately

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• Java Receive Attachment problem ?

  - by Karthick RM

  Hi to all.I use the following code to download the attachment from the mail .But it gives the ClassCastException on the Multipart declaration Exception in thread "main" java.lang.ClassCastException: com.sun.mail.imap.IMAPInputStream cannot be cast to javax.mail.Multipart at ReadAttachment.main(ReadAttachment.java:52) How do I handle IMAPInputStream? Thanks in advance !!! Message messages[] = inbox.getMessages(); for (int j = 0; j < messages.length; j++) { String mailType = messages[j].getContentType(); System.out.println("------------ Message " + (j + 1) + " ------------"); System.out.println("SentDate : " + messages[j].getSentDate()); System.out.println("From : " + messages[j].getFrom()[0]); System.out.println("Subject : " + messages[j].getSubject()); System.out.println("Type :" + messages[j].getContentType()); System.out.println("Attachment :" + messages[j].getFileName()); Multipart mp = (Multipart) messages[j].getContent(); ........... .............. System.out.println(); }

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• a way to use log4j pass values like java -DmyEnvVar=A_VALUE to my code

  - by raticulin

  I need to pass some value to enable certain code in may app (in this case is to optionally enable writing some stats to a file in certain conditions, but it might be anything generally). My java app is installed as a service. So every way I have thought of has some drawbacks: Add another param to main(): cumbersome as customers already have the tool installed, and the command line would need to be changed every time. Adding java -DmyEnvVar=A_VALUE to my command line: same as above. Set an environment variable: service should at least be restarted, and even then you must take care of what user is the service running under etc. Adding the property in the config file: I prefer not to have this visible on the config file so the user does not see it, it is something for debugging etc. So I thought maybe there is some way (or hack) to use log4j loggers to pass that value to my code. I have thought of one way already, although is very limited: Add a dummy class to my codebase com.dummy.DevOptions public class DevOptions { public static final Logger logger = Logger.getLogger(DevOptions.class); In my code, use it like this: if (DevOptions.logger.isInfoEnabled()){ //do my optional stuff } //... if (DevOptions.logger.isDebugEnabled()){ //do other stuff } This allows me to use discriminate among various values, and I could increase the number by adding more loggers to DevOptions. But I wonder whether there is a cleaner way, possibly by configuring the loggers only in log4j.xml??

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• Simple Physics Simulation in java not working.

  - by Static Void Main

  Dear experts, I wanted to implement ball physics and as i m newbie, i adapt the code in tutorial http://adam21.web.officelive.com/Documents/JavaPhysicsTutorial.pdf . i try to follow that as i much as i can, but i m not able to apply all physical phenomenon in code, can somebody please tell me, where i m mistaken or i m still doing some silly programming mistake. The balls are moving when i m not calling bounce method and i m unable to avail the bounce method and ball are moving towards left side instead of falling/ending on floor**, Can some body recommend me some better way or similar easy compact way to accomplish this task of applying physics on two ball or more balls with interactivity. here is code ; import java.awt.*; public class AdobeBall { protected int radius = 20; protected Color color; // ... Constants final static int DIAMETER = 40; // ... Instance variables private int m_x; // x and y coordinates upper left private int m_y; private double dx = 3.0; // delta x and y private double dy = 6.0; private double m_velocityX; // Pixels to move each time move() is called. private double m_velocityY; private int m_rightBound; // Maximum permissible x, y values. private int m_bottomBound; public AdobeBall(int x, int y, double velocityX, double velocityY, Color color1) { super(); m_x = x; m_y = y; m_velocityX = velocityX; m_velocityY = velocityY; color = color1; } public double getSpeed() { return Math.sqrt((m_x + m_velocityX - m_x) * (m_x + m_velocityX - m_x) + (m_y + m_velocityY - m_y) * (m_y + m_velocityY - m_y)); } public void setSpeed(double speed) { double currentSpeed = Math.sqrt(dx * dx + dy * dy); dx = dx * speed / currentSpeed; dy = dy * speed / currentSpeed; } public void setDirection(double direction) { m_velocityX = (int) (Math.cos(direction) * getSpeed()); m_velocityY = (int) (Math.sin(direction) * getSpeed()); } public double getDirection() { double h = ((m_x + dx - m_x) * (m_x + dx - m_x)) + ((m_y + dy - m_y) * (m_y + dy - m_y)); double a = (m_x + dx - m_x) / h; return a; } // ======================================================== setBounds public void setBounds(int width, int height) { m_rightBound = width - DIAMETER; m_bottomBound = height - DIAMETER; } // ============================================================== move public void move() { double gravAmount = 0.02; double gravDir = 90; // The direction for the gravity to be in. // ... Move the ball at the give velocity. m_x += m_velocityX; m_y += m_velocityY; // ... Bounce the ball off the walls if necessary. if (m_x < 0) { // If at or beyond left side m_x = 0; // Place against edge and m_velocityX = -m_velocityX; } else if (m_x > m_rightBound) { // If at or beyond right side m_x = m_rightBound; // Place against right edge. m_velocityX = -m_velocityX; } if (m_y < 0) { // if we're at top m_y = 0; m_velocityY = -m_velocityY; } else if (m_y > m_bottomBound) { // if we're at bottom m_y = m_bottomBound; m_velocityY = -m_velocityY; } // double speed = Math.sqrt((m_velocityX * m_velocityX) // + (m_velocityY * m_velocityY)); // ...Friction stuff double fricMax = 0.02; // You can use any number, preferably less than 1 double friction = getSpeed(); if (friction > fricMax) friction = fricMax; if (m_velocityX >= 0) { m_velocityX -= friction; } if (m_velocityX <= 0) { m_velocityX += friction; } if (m_velocityY >= 0) { m_velocityY -= friction; } if (m_velocityY <= 0) { m_velocityY += friction; } // ...Gravity stuff m_velocityX += Math.cos(gravDir) * gravAmount; m_velocityY += Math.sin(gravDir) * gravAmount; } public Color getColor() { return color; } public void setColor(Color newColor) { color = newColor; } // ============================================= getDiameter, getX, getY public int getDiameter() { return DIAMETER; } public double getRadius() { return radius; // radius should be a local variable in Ball. } public int getX() { return m_x; } public int getY() { return m_y; } } using adobeBall: import java.awt.*; import java.awt.event.*; import javax.swing.*; public class AdobeBallImplementation implements Runnable { private static final long serialVersionUID = 1L; private volatile boolean Play; private long mFrameDelay; private JFrame frame; private MyKeyListener pit; /** true means mouse was pressed in ball and still in panel. */ private boolean _canDrag = false; private static final int MAX_BALLS = 50; // max number allowed private int currentNumBalls = 2; // number currently active private AdobeBall[] ball = new AdobeBall[MAX_BALLS]; public AdobeBallImplementation(Color ballColor) { frame = new JFrame("simple gaming loop in java"); frame.setSize(400, 400); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pit = new MyKeyListener(); pit.setPreferredSize(new Dimension(400, 400)); frame.setContentPane(pit); ball[0] = new AdobeBall(34, 150, 7, 2, Color.YELLOW); ball[1] = new AdobeBall(50, 50, 5, 3, Color.BLUE); frame.pack(); frame.setVisible(true); frame.setBackground(Color.white); start(); frame.addMouseListener(pit); frame.addMouseMotionListener(pit); } public void start() { Play = true; Thread t = new Thread(this); t.start(); } public void stop() { Play = false; } public void run() { while (Play == true) { // bounce(ball[0],ball[1]); runball(); pit.repaint(); try { Thread.sleep(mFrameDelay); } catch (InterruptedException ie) { stop(); } } } public void drawworld(Graphics g) { for (int i = 0; i < currentNumBalls; i++) { g.setColor(ball[i].getColor()); g.fillOval(ball[i].getX(), ball[i].getY(), 40, 40); } } public double pointDistance (double x1, double y1, double x2, double y2) { return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); } public void runball() { while (Play == true) { try { for (int i = 0; i < currentNumBalls; i++) { for (int j = 0; j < currentNumBalls; j++) { if (pointDistance(ball[i].getX(), ball[i].getY(), ball[j].getX(), ball[j].getY()) < ball[i] .getRadius() + ball[j].getRadius() + 2) { // bounce(ball[i],ball[j]); ball[i].setBounds(pit.getWidth(), pit.getHeight()); ball[i].move(); pit.repaint(); } } } try { Thread.sleep(50); } catch (Exception e) { System.exit(0); } } catch (Exception e) { e.printStackTrace(); } } } public static double pointDirection(int x1, int y1, int x2, int y2) { double H = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); // The // hypotenuse double x = x2 - x1; // The opposite double y = y2 - y1; // The adjacent double angle = Math.acos(x / H); angle = angle * 57.2960285258; if (y < 0) { angle = 360 - angle; } return angle; } public static void bounce(AdobeBall b1, AdobeBall b2) { if (b2.getSpeed() == 0 && b1.getSpeed() == 0) { // Both balls are stopped. b1.setDirection(pointDirection(b1.getX(), b1.getY(), b2.getX(), b2 .getY())); b2.setDirection(pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY())); b1.setSpeed(1); b2.setSpeed(1); } else if (b2.getSpeed() == 0 && b1.getSpeed() != 0) { // B1 is moving. B2 is stationary. double angle = pointDirection(b1.getX(), b1.getY(), b2.getX(), b2 .getY()); b2.setSpeed(b1.getSpeed()); b2.setDirection(angle); b1.setDirection(angle - 90); } else if (b1.getSpeed() == 0 && b2.getSpeed() != 0) { // B1 is moving. B2 is stationary. double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY()); b1.setSpeed(b2.getSpeed()); b1.setDirection(angle); b2.setDirection(angle - 90); } else { // Both balls are moving. AdobeBall tmp = b1; double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY()); double origangle = b1.getDirection(); b1.setDirection(angle + origangle); angle = pointDirection(tmp.getX(), tmp.getY(), b2.getX(), b2.getY()); origangle = b2.getDirection(); b2.setDirection(angle + origangle); } } public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { new AdobeBallImplementation(Color.red); } }); } } *EDIT:*ok splitting the code using new approach for gravity from this forum: this code also not working the ball is not coming on floor: public void mymove() { m_x += m_velocityX; m_y += m_velocityY; if (m_y + m_bottomBound > 400) { m_velocityY *= -0.981; // setY(400 - m_bottomBound); m_y = 400 - m_bottomBound; } // ... Bounce the ball off the walls if necessary. if (m_x < 0) { // If at or beyond left side m_x = 0; // Place against edge and m_velocityX = -m_velocityX; } else if (m_x > m_rightBound) { // If at or beyond right side m_x = m_rightBound - 20; // Place against right edge. m_velocityX = -m_velocityX; } if (m_y < 0) { // if we're at top m_y = 1; m_velocityY = -m_velocityY; } else if (m_y > m_bottomBound) { // if we're at bottom m_y = m_bottomBound - 20; m_velocityY = -m_velocityY; } } thanks a lot for any correction and help. jibby

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• Swing: set JFrame content area size

  - by igul222

  I'm trying to make a JFrame with a usable content area of exactly 500x500. If I do this... public MyFrame() { super("Hello, world!"); setSize(500,500); } ... I get a window whose full size is 500x500, including the title bar, etc., where I really need a window whose size is something like 504x520 to account for the window border and titlebar. How can I achieve this?

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• How to make cycle over cycles in Java?

  - by Roman

  I would like to make a cycle over the following elements: [1,2,11,12,21,22,111,112,121,122,....,222222] or for example [1,2,3,11,12,13,21,22,23,31,32,33,111,112,113,... 333333333] How can I make it in Java? In my particular case I use 4 digits (1,2,3,4) and the length of the last number can be from 1 to 10. I managed to do it in Python and PHP. In the first case I used list over lists. I started from [[1],[2],] then for every element of the list I added 1 and 2, so I got [[1,1],[1,2],[2,1],[2,2]] and so on: nchips = sum(chips) traj = [[]] last = [[]] while len(last[0]) < nchips: newlast = [] for tr in last: for d in [1,2,3,4]: newlast.append(tr + [d]) last = newlast traj += last When I did it in PHP I used number with base 3. But it was a tricky and non elegant solution. for ($i=-1; $i<=$n; $i+=1) { if ($i>-1) { $n5 = base_convert($i,10,5); $n5_str = strval($n5); $tr = array(); $found = 0; for ($j=0; $j<strlen($n5_str); $j+=1) { $k = $n5_str[$j]; if ($k==0) { $found = 1; break; } array_push($tr,$k); } if ($found==1) continue; } else { $tr = array(); } } Can it be done easily in Java?

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• Java, let CookieHandler work on only one instance.

  - by user435657

  Hi all, I don't know how CookieHandler works system wide, I did view the source of CookieHandler but found no more information except the get/set methods. Where do TCP/HTTP connections use instance of CookieHandler, which I set by CookieHandler.setDefault(...) Which source file I should refer to? URLConnection & HttpURLConnection don't seem have things to do with it. Help, thanks in advance.

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• Data structure for an ordered set with many defined subsets; retrieve subsets in same order

  - by Aaron

  I'm looking for an efficient way of storing an ordered list/set of items where: The order of items in the master set changes rapidly (subsets maintain the master set's order) Many subsets can be defined and retrieved The number of members in the master set grow rapidly Members are added to and removed from subsets frequently Must allow for somewhat efficient merging of any number of subsets Performance would ideally be biased toward retrieval of the first N items of any subset (or merged subset), and storage would be in-memory (and maybe eventually persistent on disk)

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• Set reference = null in finally block?

  - by deamon

  A colleague of mine sets reference to null in finally blocks. I think this is nonsense. public Something getSomething() { JDBCConnection jdbc=null; try { jdbc=JDBCManager.getConnection(JDBCTypes.MYSQL); } finally { JDBCManager.free(jdbc); jdbc=null; // <-- Useful or not? } } What do you think of it?

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• Capturing wildcards in java generics

  - by Rollerball

  From this orcale java tutorial: The WildcardError example produces a capture error when compiled: import java.util.List; public class WildcardError { void foo(List<?> i) { i.set(0, i.get(0)); } } After this error demonstration, they fix the problem by using a helper method: public class WildcardFixed { void foo(List<?> i) { fooHelper(i); } // Helper method created so that the wildcard can be captured // through type inference. private <T> void fooHelper(List<T> l) { l.set(0, l.get(0)); } } First, they say that the list input parameter (i) is seen as an Object: In this example, the compiler processes the i input parameter as being of type Object. Why then i.get(0) does not return an Object? if it was already passed in as such? Furthermore what is the point of using a <?> when then you have to use an helper method using <T>. Would not be better using directly which can be inferred?

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• Java - What's the most efficient way of removing a set of elements from an Array[]

  - by fraido

  I've something like this Object[] myObjects = ...(initialized in some way)... int[] elemToRemove = new int[]{3,4,6,8,...} What's the most efficient way of removing the elements of index position 3,4,6,8... from myObjects ? I'd like to implement an efficient Utility method with a signature like public Object[] removeElements(Object[] object, int[] elementsToRemove) {...} The Object[] that is returned should be a new Object of size myObjects.length - elemToRemove.length

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• create an hotspot and set an image without background (like earth icon) to my panel

  - by sirvan

  Hi I try to create an hotspot by Extends of canvas and I try to add it on a panel witch painted by images , so I must to draw an icon (image) instead of clear rectangle of the screen, to do that I override the paint method to draw the icon I want to use, so far there is no problem, the hotspot work true and the icon painted in true size I want(32,24 pixel) I try to add this hotspot after painting image on the my panel in mypanel.paint(g) that override too. The problem , I use an car icon that have no background !!(I hope you can understand me) just car icon must be show on the panel that painted with my images; But an unwanted rectangle created around the icon and made bad view, How I can paint may icon on panel without that background? Please help me.

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• Python to Java translation

  - by obelix1337

  Hello, i get quite short code of algorithm in python, but i need to translate it to Java. I didnt find any program to do that, so i will really appreciate to help translating it. I learned python a very little to know the idea how algorithm work. The biggest problem is because in python all is object and some things are made really very confuzing like sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) and "self.adj" is like hashmap with multiple values which i have no idea how to put all together. Is any better collection for this code in java? code is: [CODE] class FlowNetwork(object): def __init__(self): self.adj, self.flow, = {},{} def add_vertex(self, vertex): self.adj[vertex] = [] def get_edges(self, v): return self.adj[v] def add_edge(self, u,v,w=0): self.adj[u].append((v,w)) self.adj[v].append((u,0)) self.flow[(u,v)] = self.flow[(v,u)] = 0 def find_path(self, source, sink, path): if source == sink: return path for vertex, capacity in self.get_edges(source): residual = capacity - self.flow[(source,vertex)] edge = (source,vertex,residual) if residual > 0 and not edge in path: result = self.find_path(vertex, sink, path + [edge]) if result != None: return result def max_flow(self, source, sink): path = self.find_path(source, sink, []) while path != None: flow = min(r for u,v,r in path) for u,v,_ in path: self.flow[(u,v)] += flow self.flow[(v,u)] -= flow path = self.find_path(source, sink, []) return sum(self.flow[(source, vertex)] for vertex, capacity in self.get_edges(source)) g = FlowNetwork() map(g.add_vertex, ['s','o','p','q','r','t']) g.add_edge('s','o',3) g.add_edge('s','p',3) g.add_edge('o','p',2) g.add_edge('o','q',3) g.add_edge('p','r',2) g.add_edge('r','t',3) g.add_edge('q','r',4) g.add_edge('q','t',2) print g.max_flow('s','t') [/CODE] result of this example is "5". algorithm find max flow in graph(linked list or whatever) from source vertex "s" to destination "t". Many thanx for any idea

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• C struct written in file, open with Java

  - by DaunnC

  For example in C I have structure: typedef struct { int number; double x1; double y1; double x2; double y2; double x3; double y3; } CTRstruct;` Then I write it to file fwrite(&tr, 1, sizeof(tr), fp); (tr - its CTRstruct var, fp - File pointer); Then I need to read it with Java! I really don't know how to read struct from file... I tried to read it with ObjectInputStream(), last idea is to read with RandomAccessFile() but I also don't know how to... (readLong(), readDouble() also doesn't work, it works ofcource but doesn't read correct data). So, any idea how to read C struct from binary file with Java? If it's interesting, my version to read integer (but it's ugly, & I don't know what to do with double): public class MyDataInputStream extends DataInputStream{ public MyDataInputStream(InputStream AIs) { super(AIs); } public int readInt1() throws IOException{ int ch1 = in.read(); int ch2 = in.read(); int ch3 = in.read(); int ch4 = in.read(); if ((ch1 | ch2 | ch3 | ch4) < 0) throw new EOFException(); return ((ch4 << 24) + (ch3 << 16) + (ch2 << 8) + (ch1 << 0)); } with double we can deal the same way (like with int or with long (8bytes) & then convert to double with native func).

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• Set the amount of rows JList show (Java)

  - by Alex Cheng

  Hi all. Problem: I have a method that creates a list from the parsed ArrayList. I manage to show the list in the GUI, without scrollbar. However, I am having problem setting it to show only the size of ArrayList. Meaning, say if the size is 6, there should only be 6 rows in the shown List. Below is the code that I am using. I tried setting the visibleRowCount as below but it does not work. I tried printing out the result and it shows that the change is made. private void createSuggestionList(ArrayList<String> str) { int visibleRowCount = str.size(); System.out.println("visibleRowCount " + visibleRowCount); listForSuggestion = new JList(str.toArray()); listForSuggestion.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); listForSuggestion.setSelectedIndex(0); listForSuggestion.setVisibleRowCount(visibleRowCount); System.out.println(listForSuggestion.getVisibleRowCount()); listScrollPane = new JScrollPane(listForSuggestion); MouseListener mouseListener = new MouseAdapter() { @Override public void mouseClicked(MouseEvent mouseEvent) { JList theList = (JList) mouseEvent.getSource(); if (mouseEvent.getClickCount() == 2) { int index = theList.locationToIndex(mouseEvent.getPoint()); if (index >= 0) { Object o = theList.getModel().getElementAt(index); System.out.println("Double-clicked on: " + o.toString()); } } } }; listForSuggestion.addMouseListener(mouseListener); textPane.add(listScrollPane); repaint(); } To summarize: I want the JList to show as many rows as the size of the parsed ArrayList, without a scrollbar. Any ideas? Please help. Thanks. Please let me know if a picture of the problem is needed in case I did not phrase my question correctly.

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