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  • Why avoid Java Inheritance "Extends"

    - by newbie
    Good day! Jame Gosling said “You should avoid implementation inheritance whenever possible.” and instead, use interface inheritance. But why? How can we avoid inheriting the structure of an object using the keyword "extends", and at the same time make our code Object Oriented? Could someone please give an Object Oriented example illustrating this concept in a scenario like "ordering a book in a bookstore?" Thank you in advance.

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  • Java getResourceAsStream as local resource

    - by Dajgoro Labinac
    Before using LWJGL, I used the Graphic method, and there I displayed imageicons, and I had the picture file located in the resources. I used: ImageIcon tcard = new ImageIcon(this.getClass().getResource("RCA.png")); to load the image. Now when I load textures in LWJGL, I have to use absolute paths to locate the file: tcard = TextureLoader.getTexture("PNG", ResourceLoader.getResourceAsStream("C:/RCA.png")); I tried Googling, but I didn't find anything helpful. How can I load the image from the local resources like in the first example?

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  • java 2d game how to make a player jump

    - by user2957632
    Hi I'm making a 2d plat former running game kind of like jetpack joyride fro example were u are constantly running but there is obstacles and u need to jump over them. but I want the character to jump and come back down. here is some of my code. if (listen.ml == true) { if (y > 120) { jump = true; y -= 1; } } if (y == 121 && jump == true) { jump = false; y += 1; }

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  • Reasons behind polymorphism related behaviour in java

    - by Shades88
    I read this code somewhere class Foo { public int a; public Foo() { a = 3; } public void addFive() { a += 5; } public int getA() { System.out.println("we are here in base class!"); return a; } } public class Polymorphism extends Foo{ public int a; public Poylmorphism() { a = 5; } public void addFive() { System.out.println("we are here !" + a); a += 5; } public int getA() { System.out.println("we are here in sub class!"); return a; } public static void main(String [] main) { Foo f = new Polymorphism(); f.addFive(); System.out.println(f.getA()); // SOP 1 System.out.println(f.a); // SOP 2 } } For SOP1 we get answer 10 and for SOP2 we get answer 3. Reason for this is that you can't override variables whereas you can do so for methods. This happens because type of the reference variable is checked when a variable is accessed and type of the object is checked when a method is accessed. But I am wondering, just why is it that way? Can anyone explain me what is the reason for this behaviour

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  • Where should I start and how to progress when learning Java EE

    - by danizmax
    I know basic stuff like, what are beans, jsp, servlet, jsf and how this stuff should work together. I know how to make basic jsp page with database query for example. Now I need to know what is the best path to learn all this stuff. My plan is to learn in this order: jsp (including persistance and JSTL) servlets + beans jsf The jump to frameworks (hibernate, struts, spring, etc) Also I'm not exactly sure about JSF, is it a must to make great pages or is it just a convenience to know?

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  • How would I use JBox2d in Java?

    - by BluFire
    So I did some research and a found Box2d. I then proceeded to download it and the testbed. Now that i have it, I don't know how to properly use it. I'm looking for a clear simple answer on how to use the engine. The things I did was that I put it into a lib folder and referenced the JBox2D jar file. After that i got stuck. How can i use this to program games for android? I'm very confused since Box2d was intended for C++.

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  • Java ResourceLoader.getResourceAsStream local resource

    - by Dajgoro Labinac
    Before using lwjgl, i used the Graphic method, and there i displayed imageicons, and i had the picture file located in the resources. I used: ImageIcon tcard = new ImageIcon(this.getClass().getResource("RCA.png")); to load the image. Now when i load textures in lwjgl, i have to use absolute paths to locate the file: tcard = TextureLoader.getTexture("PNG", ResourceLoader.getResourceAsStream("C:/RCA.png")); I tried googling, but i didn't find anything helpful... How can i load the image from the local resources like in the first example?

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  • libgdx - collision detection with tiled map java

    - by user2875021
    currently, I am working on a 2d rpg game which is similar to final fantasy 1-4. I can load up a tiled map and the sprite can walk freely on the map. However, I will like to create a wall for it to stop walking through it. I created three tiled layer Background, Collision, Overhead and one Collision object layer with rectangles only. "How do I handle collisions with the object layer in the tiled map?" "Do I have to create every single rectangle that is in the object layer with Rectangle rectangle = new Rectangle() and rectangle.set(x, y, width, height)in the code?" Thank you very much in advance. Any help is greatly appreciated!

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  • Vectors with Circles Physics -java

    - by Joe Hearty
    This is a problem I've been having, When making a set number of filled circles at random locations on a JPanel and applying a gravity (a negative change in the y), each of the circles collide. I want them to have collision detection and push in the opposite direction using vectors but i don't know how to apply that to my scenario could someone help? public void drawballs(Graphics g){ g.setColor (Color.white); //displays circles for(int i = 0; i<xlocationofcircles.length-1; i++){ g.fillOval( (int) xlocationofcircles[i], (int) (ylocationofcircles[i]) ,16 ,16 ); ylocationofcircles[i]+=.2; //gravity if(ylocationofcircles[i] > 550) //stops gravity at bottom of screen ylocationofcircles[i]-=.2; //Check distance between circles(i think..) float distance =(xlocationofcircles[i+1]-xlocationofcircles[i]) + (ylocationofcircles[i+1]-xlocationofcircles[i]) ; if( Math.sqrt(distance) <16)

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  • ArrayList in Java [on hold]

    - by JNL
    I was implementing a program to remove the duplicates from the 2 character array. I implemented these 2 solutions, Solution 1 worked fine, but Solution 2 given me UnSupportedoperationException. I am wonderring why i sthat so? The two solutions are given below; public void getDiffernce(Character[] inp1, Character[] inp2){ // Solution 1: // ********************************************************************************** List<Character> list1 = new ArrayList<Character>(Arrays.asList(inp1)); List<Character> list2 = new ArrayList<Character>(Arrays.asList(inp2)); list1.removeAll(list2); System.out.println(list1); System.out.println("*********************************************************************************"); // Solution 2: Character a[] = {'f', 'x', 'l', 'b', 'y'}; Character b[] = {'x', 'b','d'}; List<Character> al1 = new ArrayList<Character>(); List<Character> al2 = new ArrayList<Character>(); al1 = (Arrays.asList(a)); System.out.println(al1); al2 = (Arrays.asList(b)); System.out.println(al2); al1.removeAll(al2); // retainAll(al2); System.out.println(al1); }

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  • java application architecture

    - by LostMohican
    We have to write an administration panel for many customers. But we want to have just one administration panel, and use it in various projects. This admin panel will have basic components such as access control logic, maker-checker system in changes, user logging and etc. It will also have reporting for the customer, logs of transaction of the customer (which can vary according to the industry such as mobile banking, banking, ticket sales). These components may have to be modified according to the business. So we are thinking about the architecture here, Is it OK to use jars of every basic components, and bring them together on a glue application? Or should we build each component as WARs and make interfaces between them? If there are any more ideas, it will be appreciated.

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  • Java - Finding distance between player and tile in array

    - by Corey
    What is the best way performance wise to do this? When I click a tile I want it to get the distance and if I am close enough I can interact with the tile. One way would be to find the tile by doing mouse / tile width when I click correct? But then how would I get that tiles position? I know how to find the distance I just don't know how to get a certain tiles position from the array when I click it

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  • Basic Java drawing program: issue with squares

    - by Caminek
    I'm trying to create a simple drawing program that creates a square where the user clicks and drags. The square displays correctly as long as either x or y remain positive with respect to the original click position. If both x and y are negative with respect to the original click position, the square grows/shrinks, but also wanders about the screen. Is there a way to swap the origin point from top-left to bottom-right or to keep the square from wandering?

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  • Map rendering Libgdx Java

    - by user3165683
    Ok, so I am trying to create a 2D non-movable random tiled map. This is what I have so far: private void generateTile(){ System.out.print("tiletry1"); while(loadedTiles != 8100){ System.out.print("tiletry"); Texture currentTile = null; int tileX = 0; int tileY = 0; if (tileX == 120); tileY = 16; tileX = 0; game.batch.begin(); switch(MathUtils.random(2)){ case 0: //game.batch.draw(tile1, tileX, tileY); System.out.print("tile1"); currentTile = tile1; break; case 1: //game.batch.draw(tile2, tileX, tileY); System.out.print("tile2"); currentTile = tile2; break; case 2: //game.batch.draw(tile3, tileX, tileY); System.out.print("tile3"); currentTile = tile3; break; } tileX+=16; loadedTiles ++; game.batch.draw(currentTile, tileX, tileY); game.batch.end(); } } However, I can't see any of the tiles and the screen just looks green. This method is above my render method which I have: camera.update(); batch.setProjectionMatrix(camera.combined); Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT); game.batch.begin(); //other render stuff Why am I not able to see the tiles?

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  • Please Critique Code (Java, Java2D, javax.swing.Timer)

    - by Trizicus
    Learn by practice right? Please critique and suggest anything! Thanks :) import java.awt.EventQueue; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import java.awt.event.MouseMotionListener; import javax.swing.JFrame; public class MainWindow { public static void main(String[] args) { new MainWindow(); } JFrame frame; GraphicsPanel gp = new GraphicsPanel(); MainWindow() { EventQueue.invokeLater(new Runnable() { public void run() { frame = new JFrame("Graphics Practice"); frame.setSize(680, 420); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); gp.addMouseListener(new MouseListener() { public void mouseClicked(MouseEvent e) {} public void mousePressed(MouseEvent e) {} public void mouseReleased(MouseEvent e) {} public void mouseEntered(MouseEvent e) {} public void mouseExited(MouseEvent e) {} }); gp.addMouseMotionListener(new MouseMotionListener() { public void mouseDragged(MouseEvent e) {} public void mouseMoved(MouseEvent e) {} }); frame.add(gp); } }); } } GraphicsPanel: import java.awt.BorderLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.JPanel; import javax.swing.Timer; public class GraphicsPanel extends JPanel { Test t; Timer test; GraphicsPanel() { t = new Test(); setLayout(new BorderLayout()); add(t, BorderLayout.CENTER); test = new Timer(17, new Gameloop(this)); test.start(); } class Gameloop implements ActionListener { GraphicsPanel gp; Gameloop(GraphicsPanel gp) { this.gp = gp; } public void actionPerformed(ActionEvent e) { try { t.incX(); gp.repaint(); } catch (Exception ez) { } } } } Test: import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Image; import java.awt.Toolkit; import javax.swing.JComponent; public class Test extends JComponent { Toolkit tk; Image img; int x, y; Test() { tk = Toolkit.getDefaultToolkit(); img = tk.getImage(getClass().getResource("images.jpg")); this.setPreferredSize(new Dimension(15, 15)); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); g2d.setColor(Color.red); g2d.drawString("x: " + x, 350, 50); g2d.drawImage(img, x, 80, null); g2d.dispose(); } public void incX() { x++; } }

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  • Which Java version do you mostly (have to) work with?

    - by ferdystschenko
    While from version 5 on, Java provides many extremely useful features like annotations, enums, generics, etc., 1.4 is still in use in many enterprise projects. So I'm wondering what the chances are that you still have to work with 1.4, thus being forced to go without JPA, EJB3 etc. In your answer, please also state the branch of company you work for. Which are the reasons for not switching to Java 5? Thanks, Armin

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  • Help me with this java program

    - by aser
    The question : Input file: customer’s account number, account balance at beginning of month, transaction type (withdrawal, deposit, interest), transaction amount Output: account number, beginning balance, ending balance, total interest paid, total amount deposited, number of deposits, total amount withdrawn, number of withdrawals package sentinel; import java.io.*; import java.util.*; public class Ex7 { /** * @param args the command line arguments */ public static void main(String[] args) throws FileNotFoundException { int AccountNum; double BeginningBalance; double TransactionAmount; int TransactionType; double AmountDeposited=0; int NumberOfDeposits=0; double InterestPaid=0.0; double AmountWithdrawn=0.0; int NumberOfWithdrawals=0; boolean found= false; Scanner inFile = new Scanner(new FileReader("Account.in")); PrintWriter outFile = new PrintWriter("Account.out"); AccountNum = inFile.nextInt(); BeginningBalance= inFile.nextDouble(); while (inFile.hasNext()) { TransactionAmount=inFile.nextDouble(); TransactionType=inFile.nextInt(); outFile.printf("Account Number: %d%n", AccountNum); outFile.printf("Beginning Balance: $%.2f %n",BeginningBalance); outFile.printf("Ending Balance: $%.2f %n",BeginningBalance); outFile.println(); switch (TransactionType) { case '1': // case 1 if we have a Deposite BeginningBalance = BeginningBalance + TransactionAmount; AmountDeposited = AmountDeposited + TransactionAmount; NumberOfDeposits++; outFile.printf("Amount Deposited: $%.2f %n",AmountDeposited); outFile.printf("Number of Deposits: %d%n",NumberOfDeposits); outFile.println(); break; case '2':// case 2 if we have an Interest BeginningBalance = BeginningBalance + TransactionAmount; InterestPaid = InterestPaid + TransactionAmount; outFile.printf("Interest Paid: $%.2f %n",InterestPaid); outFile.println(); break; case '3':// case 3 if we have a Withdraw BeginningBalance = BeginningBalance - TransactionAmount; AmountWithdrawn = AmountWithdrawn + TransactionAmount; NumberOfWithdrawals++; outFile.printf("Amount Withdrawn: $%.2f %n",AmountWithdrawn); outFile.printf("Number of Withdrawals: %d%n",NumberOfWithdrawals); outFile.println(); break; default: System.out.println("Invalid transaction Tybe: " + TransactionType + TransactionAmount); } } inFile.close(); outFile.close(); } } But is gives me this : Exception in thread "main" java.util.InputMismatchException at java.util.Scanner.throwFor(Scanner.java:840) at java.util.Scanner.next(Scanner.java:1461) at java.util.Scanner.nextInt(Scanner.java:2091) at java.util.Scanner.nextInt(Scanner.java:2050) at sentinel.Ex7.main(Ex7.java:36) Java Result: 1

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  • Is there any library to represent SQL queries as objects in Java code?

    - by Pregzt
    I was wondering if there is any library that can be used to represent SQL queries as objects in Java. In the code I have plenty of static variables of type java.lang.String that are hand written SQL queries. I would be looking for library having a nice fluent API that allows me to represent the queries as objects rather than strings. Example: Query q = select("DATE", "QUOTE") .from("STOCKMARKET") .where(eq("CORP", "?")) .orderBy("DATE", DESC);

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  • Java file manager won't load in Firefox

    - by Arthur
    I am using Webmin and I can't get the file manager to load in Firefox. It is a simple, Java based file manager. When I try to load it I get the following error: This module requires java to function, but your browser does not support java Internet Explorer works fine and I have yet to try on Chrome. Java is installed and I have the same problem on Windows and Linux. Java seems to work fine with everything else, with the exception of webcams. Any advice on the issue would be appreciated. Edit: I just checked and it doesn't work in Chrome either.

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  • Disable Java Plugin in Google Chrome?

    - by Jeff Atwood
    This is the second time I've had a drive-by executable installed on my machine using the following: Google Chrome 6 (latest) Windows 7, UAC on This happened while I was browsing for images to add to a gaming.se post; one of the sites I visited (to get an image of a transfer cable) must have had drive-by browser exploit code running. UAC alerted me that a weird temporary executable wanted to run, and I declined, but I still got the fake antivirus executable running on my machine. Sigh.. I do have Java installed because I upload stuff monthly to clearbits.net and their uploader is a Java plugin. So my best guess is, websites are doing drive-by installs using the massive numbers of zero-day vulnerabilities in the Java browser plugins. For now, I have uninstalled Java, which works. But I wondered if I could disable the Java plugin in Google Chrome instead. So, how do you disable these vulnerable plugins in Google Chrome? I can't find the UI.

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  • Installing Java on a Virtual Private Server

    - by Martin Rowe
    I have recently managed to get my employer to pay for a vps. I teach and asked the vps provider to enable Perl, Python, Ruby, Tomcat and Java. They've done the first four (really quickly) but have got back to me asking which parts of Java I need. I think the Java Virtual Machine is a given but what other S/W do I need to get installed? I think by getting the vps I now have the chance to teach Enterprise Java and want to get into Java Message Server and Enterprise patterns. Can I get Glassfish installed or is that a silly question? What about servlets and beans? Thanks in anticipation Martin Rowe

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  • how to solve out of memory error in java in amazon ec2 server

    - by sathishkumar
    can anyone explain about this error message? we are using IBM jre to run java application Its occupying more space on the server. JVMDUMP006I Processing dump event "systhrow", detail "java/lang/OutOfMemoryError" - please wait. JVMDUMP006I Processing dump event "systhrow", detail "java/lang/OutOfMemoryError" - please wait. JVMDUMP032I JVM requested Heap dump using '/home/sathish/jetty6/heapdump.20110417.114115.18926.0001.phd' in response to an event JVMDUMP010I Heap dump written to /home/sathish/jetty6/heapdump.20110417.114115.18926.0001.phd JVMDUMP032I JVM requested Heap dump using '/home/sathish/jetty6/heapdump.20110417.114115.18926.0002.phd' in response to an event JVMDUMP010I Heap dump written to /home/sathish/jetty6/heapdump.20110417.114115.18926.0002.phd JVMDUMP032I JVM requested Heap dump using '/home/sathish/jetty6/heapdump.20110417.114115.18926.0003.phd' in response to an event JVMDUMP010I Heap dump written to /home/sathish/jetty6/heapdump.20110417.114115.18926.0003.phd JVMDUMP032I JVM requested Java dump using '/home/sathish/jetty6/javacore.20110417.114115.18926.0004.txt' in response to an event JVMDUMP010I Java dump written to /home/sathish/jetty6/javacore.20110417.114115.18926.0004.txt

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  • .desktop shortcuts aren't working for java applications in LXDE

    - by chaz
    I just installed minecraft on my LXDE desktop/Lubuntu machine and I'm trying to create a .desktop file on the desktop that executes java -jar ~/minecraftlauncher.jar. The command works in bash scripts and the terminal but refuses to work when I click on my .DESKTOP shortcut which is suppose to execute the same command. I've experimented with other jars and they can't seem to start too. Here is my xsession log: ** (pcmanfm:1572): DEBUG: launch command: <java -jar ~/Downloads/minecraft_server.jar> ** (pcmanfm:1572): DEBUG: sn_id = pcmanfm-1572-administrator-Dimension-3000-java-14_TIME14031891 Unable to access jarfile ~/Downloads/minecraft_server.jar ** (pcmanfm:1572): DEBUG: launch command: <java -jar ~/minecraftlauncher.jar> ** (pcmanfm:1572): DEBUG: sn_id = pcmanfm-1572-administrator-Dimension-3000-java-15_TIME14070158 Unable to access jarfile ~/minecraftlauncher.jar UPDATE: Whoops, it seems to work when I give an absolute path. I guess the home path is something else. UPDATE: I guess X doesn't resolve the home specifier. I ran a .desktop file that executed a script that outputs the current directory, and it seems to be correct.

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  • Tuning OpenVZ Containers to work better with Java?

    - by Daniel
    I have a 8 GB RAM Server (Dedicated) and currently have KVM Virtual Machines running on there (successfully) however i'm considering moving to OpenVZ as KVM seems a bit overkill with a lot of overhead for what i use it for. In the past i have used OpenVZ Containers, hosted by myself and from other providers and Java doesn't seem to work well with them.. One example is that if i give a container 2 GB RAM ( No burst) (with or without vswap doesn't matter) a java instance can only be tuned to use at very most 1500 MB of that RAM (-Xmx, -Xms). Ideally, i wish to be able to create "Mini" containers with about 256MB, 512MB, 768 RAM and run some java instances in them. My question is: I'm trying to find an ideal way to tune a OpenVZ container configuration to work better with Java memory. Please, don't suggest anything related to Java settings, i'm looking for OpenVZ specific answers.. Though i welcome any suggestion if you feel it may help me. Much Appreciated, Daniel

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