bgaechter - blog

Netbeans 7.3 crashes on fedora 17

2012-10-18T14:40:00.001+02:00

After installing the new netbeans 7.3 i noticed that it often (almost always) crashes while starting up. Sometimes it doesn't even show a splash screen.

I figured out that this is because of the openJDK. After installing and setting up Oracles JDK everything worked fine.

Download the latest JDK from oracle. And install the package it using rpm.

rpm -Uvh jdk-*

Then install it with the alternatives command

## java ##
alternatives --install /usr/bin/java java /usr/java/jdk1.7.0_07/jre/bin/java 20000
## javaws ##
alternatives --install /usr/bin/javaws javaws /usr/java/jdk1.7.0_07/jre/bin/javaws 20000
 
## Java Browser (Mozilla) Plugin 32-bit ##
alternatives --install /usr/lib/mozilla/plugins/libjavaplugin.so libjavaplugin.so /usr/java/jdk1.7.0_07/jre/lib/i386/libnpjp2.so 20000
 
## Java Browser (Mozilla) Plugin 64-bit ##
alternatives --install /usr/lib64/mozilla/plugins/libjavaplugin.so libjavaplugin.so.x86_64 /usr/java/jdk1.7.0_07/jre/lib/amd64/libnpjp2.so 20000
 
## Install javac only if you installed JDK (Java Development Kit) package ##
alternatives --install /usr/bin/javac javac /usr/java/jdk1.7.0_07/bin/javac 20000
alternatives --install /usr/bin/jar jar /usr/java/jdk1.7.0_07/bin/jar 20000

Now you can set up Oracles JDK as your default java runtime using this command.

alternatives --config java

Try to start Netbeans, it should start without crashing or freezing.

Find all backup files (ending with ~) in your home directory

2012-10-18T14:32:00.002+02:00

Every Linux users who edits text files using some "traditional" editors like vi, emacs, kate or gedit will find some backup files which end with ~ in his directory. These files are not really needed anymore and can be deleted. I personally like to look at these files before i delete them. This is a simple script to find these files and show their size.

for i in $(find ~ -name '*~'); do echo ${i}; stat -c %s ${i}; done

If you don't need this files anymore you can delete them with this command

find ~ -name '*~' | xargs rm

Fork bomb

2012-10-03T12:52:00.000+02:00

This is nothing useful though i think it's interesting. As i saw it, it reminded me of one of my first batch files: The infinite loop of starting new command prompts. But this one is much more elegant.

:() { : | :& };:

The code declares a function called : which calls itself two times using a pipe. At the end you call : again. This leads to an exponential spawn of new processes. It won't finish unless there your system can't spawn more processes and this only happens if you run out of resources. That could force you to restart your computer. As i said nothing useful...

Trigo Calc released

2012-08-27T16:36:00.000+02:00

TrigoCalc is a tool which uses trigonometry formulas to find the missing numbers in a triangle. TrigoCalc doesn't just provide the results it also shows the computations in a human readable format. Therefore it's specially useful for students.

There is an offline version, which requires jre 7 but there is also an online version that just requires a browser. The online version also runs on smart phones.
View the TrigoCalc website.

Django syncdb can't create super user

2012-07-26T11:24:00.001+02:00

I was just setting up a new webpage using the django framework. But as i used the syncdb command (which creates the database and also adds a superuser) i received this error:

File "/usr/local/lib/python2.6/dist-packages/django/contrib/auth/management/__init__.py", line 85, in get_system_username    
return getpass.getuser().decode(locale.getdefaultlocale()[1])

The site was working normal but i couldn't add any content without a super user account.

manage.py createsuperuser --username=joe --email=joe@example.com

Didn't help a lot since i received the same error. So i used the shell to create a user manually:

$ python manage.py shell
>>> from django.contrib.auth.models import User
>>> users = User.objects.all()
>>> users
[]

No users here, so let's create a new superuser.

>>> u = User.objects.create_user('benny', 'benny@bgaechter.ch', 'bennypw')
>>> u.is_staff  =  True
>>> u.is_superuser = True
>>> u.save()

Now you should be able to login. Note: You should not use the "set_password" function to change a users password. There is a special command for that:

manage.py changepassword username

Netbeans: JVM creation failed

2012-07-03T10:59:00.002+02:00

Netbeans seems to have a problem if your 64 bit system has more than 4 GB RAM. Obviously it can't address the memory and quits with "JVM creation failed".

The solution is very easy. Just go to the netbeans.conf file. On Linux this is typically in the /etc directory. On Windows you have a folder called etc in your application folder (should be in C:\Program Files (x86)\Netbeans ). Open it with your preferred editor and add -J-Xmx512m to netbeans_default_options (at line 6). It should now look like this:

netbeans_default_options=".... -JDsun.zip.disableMemoryMapping=true -J-Xmx512m"

Save and close the file and Netbeans should start again.

KDE Shut down, Log out and Restart not working

2012-04-05T15:00:00.001+02:00

As I switched to KDE a few days ago, the Shut down didn't work. I found out that this is because of some strange interaction between the sound system and the log out mechanism. However to avoid this bug just disable the log out sound in your system settings.

Go to System settings ->Notifications ->Select KDE Workspace in the Event Source drop down menu and disable the logout sound.

Use trend lines in Numbers

2012-03-31T18:14:00.001+02:00

We had a physics experiment and I used Numbers on my Macbook to write down the results. I created a scatter diagram out of the data. Now i wanted to lay a trendline (also known as line of best fit) through the points. Numbers hide this function a little bit but i finally found it here.

Open the informations menu, click on your diagram and expand it. You will see the options for trend lines(linear, logarithmic, exponential, etc.) and failure correction.

Import images from Canon camera on Gentoo

2012-03-10T13:12:00.000+01:00

I found a very nice tool to import my images from my camera. I have to use this tool because my Canon EOS 40D can't be mounted for some reason. That's how it looks when i try to mount:

gvfs-mount "gphoto2://[usb:003,018]/" 
Error mounting location: volume doesn't implement mount

Install gphoto2

emerge gphoto2

Then go to the directory where you want to import your files, make sure your camera is detected correctly and execute this command

gphto2 --auto-detect
gphoto2 -P

That's all.

But gphoto can do much more. You can, for example, see how many images you took with the camera, change the whole configuration or capture images directly from your computer. It's worth to read the man page

Install Spotify on Gentoo

2012-02-14T18:52:00.000+01:00

Spotify currently offers stable Windows and Mac OS X version and a unstable Linux release.
You can choose to run the unstable linux client or the windows client using wine. I tried both.

The Linux release
If you choose the Linux release you can choose between a deb and a rpm package. Both should work the sam way. I went with the deb package because I am already familiar with that format. Just unpack it and place everything as it is in the archived folders:

ar vx spotify-client-qt_0.6.6.10.gbd39032.58-1_amd64.deb
tar -xzvf data.tar.gz
cp -r ./usr/* /usr/

Then try to start spotify:

spotify

Got libssl error? Gentoo comes already with the new version while spotify requiers an older one. Just install it as a slot:

emerge openssl:0.9.8

Now run it again. A login screen pops up. After the login in, spotify crashes. So Linux version is, at least here, not just unstable it's unusable.

The Windows release with Wine
I downloaded the windows binary and tried to install it with wine. The setup worked and at the end of the installation I got a desktop icon. After a double click on it the login screen pops up and as I enter my credentials spotify crashes, again.

Looks like I have to wait until I can use spotify here....

UPDATE
The unofficial Ebuild
I started searching the web for a solution. Finally I found a Ebuild that works fine. Just download it and follow the Gentoo handbook.

Concrete5 display attribute using php block

2012-01-22T14:33:00.000+01:00

//Create a User object (of the current User)
$u = new User();
//Creat a UserInfo object with the user ID
$ui = UserInfo::getByID($u->getUserID());
//Get the Value of your user Attribute
$value = $ui->getAttribute('YourAttributeName');
//Print it out
echo "Your Value: ".$value;

That's a simple example on how to use your (custom) attributes in concrete5. For furhter information consult the concrete5 documentation.

Eclipse auto complete is not working

2011-12-30T00:50:00.001+01:00

Today my Eclipse auto complete was turned off. I didn't change anything, but it decided not to work anymore. I went through the settings and finally turned it on again. To spare you the search here a screenshot:

Just set the tick at "Java Type Proposals" and it will work again.

Run a minecraft server on Debian 6

2011-11-26T23:40:00.001+01:00

Requirements
The Minecraft server is written in java, therefore java runtime environment is required. Check your java installation with this command:

java --version

If you get an error message saying "command java not found" you can install java using this command:

apt-get install default-jre

Installation
Let's start the installation. I would recommend to create a separate user for running the server. You should not use root to run the server for security reason.

useradd -m minecraft
passwd minecraft

Create a directory for the server and download as user "minecraft" the server software:

su minecraft
mkdir server
cd server
wget https://s3.amazonaws.com/MinecraftDownload/launcher/minecraft_server.jar?

Now you can run the server directly from here or you can use a script that helps you running the server in background. You can specify the maximun and minimun amount of RAM which is used by the server. But keep in mind that java produces an overhead. In my case it's about 40% to 60% (depending on runtime and connected users).

And finally start your server:

java -Xms32M -Xmx1024M -jar minecraft_server.jar nogui

I recommend to have at least 1024 Mb for your server.

Alt Key doesn't work in Gedit on Mac OS X Lion

2011-10-13T00:20:00.000+02:00

I just installed Gedit on my Mac because it's my favorite text editor. After a while (to be exact as I wanted to comment out a line of python code) I noticed that the alt key doesn't work. I started a google search where I found a lot of websites recommending to change X11 settings or copy the Xmodmap around and other things. I tried everything but it didn't help. I still couldn't comment out that line. Another trial of google search brought me to the solution.

Right click in the edit area -> Input Methods -> Multipress

And finally I could comment out that line of code. Thanks to old Nabble.

Swisscom “centro grande” dhcp dns problems

2011-09-27T18:41:00.000+02:00

Today I couldn’t reach any web page. I discovered that i can reach servers through their IP but I can’t resolve their names. The DNS entry I receive via DHCP from my modem is my modem itself.

I changed it to a public DNS server (like 8.8.8.8 or 8.8.6.6 for the Google DNS servers) and: here we go. I was able to reach everything as usual. The strange thing: sometimes it works with the DNS assigned via DHCP. Wondering what’s wrong...

Arch Linux / Windows Dual Boot - Time Problems

2011-09-22T17:04:00.000+02:00

I just installed Windows for some testing purposes on my machine. Of course as dual boot. I found out that the clock goes wrong every time I switch between Arch Linux and Windows. There are two ways to fix this problem:

Set Arch Linux to local time and remove hwclock from the DAEMONS array in /etc/rc.conf (Windows will take care of hardware clock corrections).

Set Arch Linux to UTC, and make Windows use UTC too (a quick registry fix is needed, see this page for instructions). Also, be sure to prevent Windows from synchronizing the time with the Internet, as it will make the hardware clock use localtime again. If you want such functionality (NTP sync), you should use openntpd on your Arch Linux installation instead.

WebSVN Access Control using htpasswd

2011-09-03T10:56:00.001+02:00

If you do not need to do an advanced rights management (for example give different people rights for different repositories) the easiest way, in my opinion, is to set the access rights using a htpasswd file. You need to create the file and add your user. Use the following command:

htpasswd -c /etc/apache2/dav_svn.passwd user

Then you have to tell apache that you want to use this file for access control. This doesn’t happen in any of the virtual host files (you could probably do it there but it’s not the clean way). WebSVN comes with a file called apache.conf (located in /etc/websvn/apache.conf ) Just paste these lines at the bottom of the file:

AuthType Basic
AuthName "Subversion Repository"
AuthUserFile /etc/apache2/dav_svn.passwd
Require valid-user

And you’re done. Next time you visit your websvn website you will be asked for a user name and password.

Read GET parameters using Javascript

2011-07-29T11:01:00.000+02:00

Reading get parameters with javascript can't be done using a default function. But it's quiet easy if you play around with window.location.href and some regular expressions. Here is my solution:

function parseGet( name )
{
  name = name.replace(/[\[]/,"\\\[")
  .replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
  var results = regex.exec( window.location.href );
  if( results == null )
    return "";
  else
    return results[1];
}

Usage:

parseGet('getParam');

JavaFX 2.0 "Avoid The Red Balls"

2011-06-29T13:40:00.001+02:00

In a comment to my article „JavaFX avoid the red balls“ i was pointed to JavaFX 2.0. The greatest difference between JavaFX 1.x and 2.0 is that in 2.0 you can write your applications now in Java. The support for JavaFX-Script has been completely dropped. Therefore I ported my application from 1.x to 2.0.

JavaFX is very powerful in creating user interfaces with emphasis on look and feel and design. I was able to port my App without any greater issues. Most of the code was usable as it was I just had to change the syntax. The greatest difference was the use of “AnimationTimer“ instead of “timeline”. The new version and the source code (as a netbeans project) is available here. Here is the JavaFX 2.0 code:

/*
 * Copyright 2011, Benny Gächter
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jfxtest;

import javafx.event.Event;
import javafx.event.EventHandler;
import javafx.scene.input.MouseEvent;
import java.util.Random;
import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventType;
import javafx.scene.Group;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.effect.BoxBlur;
import javafx.scene.paint.Color;
import javafx.scene.paint.Paint;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.StrokeType;
import javafx.stage.Stage;

/**
 *
 * @author Benny Gächter
 */
public class JFXTest extends Application implements EventHandler {

    static int APP_WIDTH = 800;
    static int APP_HEIGHT = 600;
    double mouseX = 0.0;
    double mouseY = 0.0;
    Random random = new java.util.Random();
    int state = 1;
    int counter = 0;
    double currentRuntime;
    Rectangle player;
    long lastUpdate = 0;
    long startTime = 0;
    final Group balls = new Group();
    Group root = null;
    AnimationTimer timer = null;

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
 Application.launch(JFXTest.class, args);
    }

    @Override
    public void start(Stage primaryStage) {
 primaryStage.setTitle("Red Balls JavaFX 2.0");
 lastUpdate = System.currentTimeMillis();

 root = new Group();
 Scene scene = new Scene(root, APP_WIDTH, APP_HEIGHT, Color.WHITE);
 scene.addEventHandler(EventType.ROOT, this);

 player = new Rectangle(20, 20, Color.BLACK);

 root.getChildren().add(player);


 for (int i = 0; i < 15; i++) {
     MyCircle ball = new MyCircle(15, Color.RED);
     ball.setStrokeType(StrokeType.OUTSIDE);
     ball.setStroke(Color.DARKRED);
     ball.setStrokeWidth(4);
     ball.setCenterX(random.nextInt(APP_WIDTH - 15));
     ball.setCenterY(random.nextInt(APP_HEIGHT - 15));

     if (random.nextInt(100) % 2 == 0) {
  ball.setVx(1);
     }
     if (random.nextInt(100) % 2 == 0) {
  ball.setVy(1);
     }
     balls.getChildren().add(ball);
     balls.setEffect(new BoxBlur(2, 2, 1));
 }

 root.getChildren().add(balls);
 startTime = System.currentTimeMillis();

 final Label time = new Label("Time :");
 time.setLayoutX(50);
 time.setLayoutY(20);
 time.setScaleX(2);
 time.setScaleY(2);
 time.setScaleZ(2);
 root.getChildren().add(time);

 timer = new AnimationTimer() {

     @Override
     public void handle(long l) {
  if (state == 1) {
      if (System.currentTimeMillis() > lastUpdate + 20) {
   lastUpdate = System.currentTimeMillis();
   time.setText("Time : " + (System.currentTimeMillis() - startTime) / 1000 + " s");
   for (Node ball : balls.getChildren()) {
       MyCircle AI = (MyCircle) ball;

       //bounce from walls
       if (AI.getCenterX() + AI.getVx() < 15) {
    AI.vx = -AI.vx;
       }
       if (AI.getCenterX() + AI.vx > APP_WIDTH - 15) {
    AI.vx = -AI.vx;
       }

       if (AI.getCenterY() + AI.vy < 15) {
    AI.vy = -AI.vy;
       }
       if (AI.getCenterY() + AI.vy > APP_HEIGHT - 15) {
    AI.vy = -AI.vy;
       }


       if (AI.getCenterX() >= mouseX && AI.getCenterX() <= mouseX + 10) {
    if (AI.getCenterY() + 15 >= mouseY - 10
     && AI.getCenterY() - 15 <= mouseY) {
        AI.vy = -AI.vy;
        state = 2;
    }
       } else if (AI.getCenterY() >= mouseY - 10
        && AI.getCenterY() <= mouseY) {
    if (AI.getCenterX() + 15 >= mouseX
     && AI.getCenterX() - 15 <= mouseX + 10) {
        AI.vx = -AI.vx;
        state = 2;

    }
       }
       //calculate new position
       AI.setCenterX(AI.getCenterX() + AI.vx);
       AI.setCenterY(AI.getCenterY() + AI.vy);

       //increase speed
       AI.vx = AI.vx * 1.002;
       AI.vy = AI.vy * 1.002;
   }
      }
  } else {
      this.stop();
      setGameoverScreen();
  }
     }
 };
 timer.start();

 primaryStage.setScene(scene);

 primaryStage.setVisible(true);

    }

    public void setGameoverScreen() {
 final Button restart = new Button();
 restart.setText("Restart");
 restart.setLayoutX(APP_WIDTH / 2);
 restart.setLayoutY(APP_HEIGHT / 2);
 restart.setScaleZ(4);
 restart.setScaleX(4);
 restart.setScaleY(4);
 root.getChildren().add(restart);

 restart.setOnAction(new EventHandler() {

     @Override
     public void handle(ActionEvent e) {
  for (Node ball : balls.getChildren()) {
      MyCircle buf = (MyCircle) ball;
      buf.setCenterX(random.nextInt(APP_WIDTH - 15));
      buf.setCenterY(random.nextInt(APP_HEIGHT - 15));

      if (random.nextInt(100) % 2 == 0) {
   buf.setVx(1);
      } else {
   buf.setVx(-1);
      }
      if (random.nextInt(100) % 2 == 0) {
   buf.setVy(1);
      } else {
   buf.setVy(-1);
      }
  }

  root.getChildren().remove(restart);
  state = 1;
  timer.start();
  startTime = System.currentTimeMillis();

     }
 });
    }

    public void handle(Event event) {
 if (event instanceof MouseEvent) {
     MouseEvent e = (MouseEvent) event;
     mouseX = e.getX();
     mouseY = e.getY();

     if (mouseX > APP_WIDTH - 20) {
  mouseX = APP_WIDTH - 20;
     }
     if (mouseY > APP_HEIGHT - 20) {
  mouseY = APP_HEIGHT - 20;
     }
     if (mouseX < 0) {
  mouseX = 1;
     }
     if (mouseY < 0) {
  mouseY = 1;
     }

     player.setX(mouseX);
     player.setY(mouseY);
 }
    }

    class MyCircle extends Circle {

 public double vy;
 public double vx;

 public MyCircle(double centerX, double centerY, double radius, Paint fill) {
     super(centerX, centerY, radius, fill);
     setVel();
 }

 public MyCircle(double centerX, double centerY, double radius) {
     super(centerX, centerY, radius);
     setVel();
 }

 public MyCircle() {
     setVel();
 }

 public MyCircle(double radius, Paint fill) {
     super(radius, fill);
     setVel();
 }

 public MyCircle(double radius) {
     super(radius);
     setVel();
 }

 public double getVx() {
     return vx;
 }

 public void setVx(int vx) {
     this.vx = vx;
 }

 public double getVy() {
     return vy;
 }

 public void setVy(int vy) {
     this.vy = vy;
 }

 private void setVel() {
     vx = -1;
     vy = -1;
 }
    }
}

MySQL Database network access

2011-06-27T13:14:00.002+02:00

It’s not very difficult to configure your MySQL Database to listen to other machines in the network but it obviously leads to confusion sometimes. There are basically two options which allow your Database to listen to TCP/IP connections. They need to be done in the my.cnf file (usually located in /etc/mysql/my.cnf).

#SkipNetworking
bind-address 0.0.0.0

If you set bind-address to 0.0.0.0 your server will accept connections from any client. You can also specify a single client by replacing 0.0.0.0 by an address (for example 192.168.1.100). To disable external TCP/IP connections set bind-address to 127.0.0.1. The server will now only accept connections from the local host. If you uncomment SkipNetworking the server won't accept TCP/IP connections at all.

Multimedia support for Scientific Linux 6, / RHEL 6

2011-06-16T10:22:00.000+02:00

I just tried out Scientific Linux 6 on my home machine. Scientific Linux is a customized and unbranded Red Hat Enterprise Linux made by CERN and Fermilab. Therefore it's very stable and made to work. But even for working it's nice to play mp3 music oder view mpeg films.
To do so you have to enable the RPMForge repository by installing a package. Go to System => Administration => Add/Remove Software and install the package:

After this you can install the following packages for full multimedia support:

yum install ffmpeg libdvdcss libdvdread libdvdnav libdvdplay lsdvd mplayer gxine gstreamer-plugins-good gstreamer-plugins-bad-free-extras gstreamer-plugins-ugly libcdaudio w3m libx264 mjpegtools libsidplay libquicktime libkate automake autoconf jna gc libid3tag amrwb gstreamer-java-swt gstreamer-java gstreamer-ffmpeg gstreamer-vaapi

If you want to install vlc keep in mind that vlc doesn't work with libmodplug from epel repository. You have to add the follwoing line to your /etc/yum.repo.d/epe.repo and epel.testing.repo:

exclude=libmodplug

Find file duplicates using a bash script

2011-06-14T14:07:00.000+02:00

This script is based on a script found in this blog. It searches recursively through the current directory and creates a script to remove all duplicate files. The script compares the md5 check sums of the files so it's able to compare binary files. It's a shell script therefore it will run on any machine with a bash shell (it might work with any other shell as well i didn't test it...).

#! /bin/sh
echo "scanning ..."
OUTF=rem-duplicates.sh;
echo "#! /bin/sh" > $OUTF;
echo "#"$OUTF >> $OUTF;
echo "" >> $OUTF;
find "$@" -type f -exec md5sum {} \; |
 sort --key=1,32 | uniq -w 32 -d --all-repeated=separate |
 sed -r 's/^[0-9a-f]*( )*//;s/([^a-zA-Z0-9./_-])/\\\1/g;s/(.+)/#rm \1/' >> $OUTF ;
chmod a+x $OUTF;
if [ -n "${EDITOR+x}" ];then
    $EDITOR $OUTF
else
    nano $OUTF
fi
echo "Do you want to execute the script? [y/n]?"
read answer
if [ $answer == "y" ]; then
    ./$OUTF
fi

Install gwtDeveloper extension in Oracle's jDeveloper

2011-05-27T10:06:00.000+02:00

I just experienced that installing the gwtDeveloper is not as easy as installing any other extension in Oracle's jdeveloper.

After a while i found out that gwtDeveloper should be in oracle's partner extensions. But a click on the download link leads me to a "404 page not found". I looked around on the web page and after a while i found the new download link.

When the download is finished all you have to do is go to Help => Check for Updates =>Choose Install from local File and click next and then finish. After a restart you are able to use the gwtDeveloper extension.

openSUSE and the rtl8192se wireless chip

2011-04-13T17:35:00.002+02:00

I installed reinstalled my netbook (an asus 1201n) again to try another linux distribution. This time i tried openSUSE. Very similair to fedora opensuse didn't inlucde the right drivers so i had to install them by myself. This is how i did it.

Get the driver from realtek website.
Then install the missing depencies.
After that you can compile the driver, install it an ensure the module is loaded and your card is recognized

zypper install automake make kernel-desktop-devel kernel-syms gcc
make   
make install
modprobe r8192se_pci
iwconfig

Javafx: avoid the red balls

2011-03-28T12:33:00.004+02:00

This weekend i took a look at javafx. After watching some video tutorials I felt able to develop my own application. I decided to write a simple game. It’s all about avoiding the red balls with your black square. And see how long you can escape.

The game covers a lot of things from collision detection to visual effects like inner shadows. If you want to play the game: click here. It’s probably a good idea having a look at the game before stepping through the code so you already know what I am talking about.

So let’s step through the code. You can also download the code as Netbeans project.

/*
 * Copyright 2011, Benny Gächter
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javafxapp;

import javafx.animation.KeyFrame;
import javafx.scene.paint.Color;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Flow;
import javafx.scene.text.Text;
import javafx.animation.Timeline;
import javafx.scene.Node;
import javafx.scene.CustomNode;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.transform.Translate;
import javafx.scene.text.Font;
import javafx.scene.Group;
import javafx.scene.control.Button;
import javafx.scene.effect.InnerShadow;
import javafx.scene.control.Hyperlink;
import javafx.stage.AppletStageExtension;

// Height and Width of this Application
def APP_WIDTH = 500;
def APP_HEIGHT = APP_WIDTH;
//Variables for mouse coordinates
var mouseX = 0.0;
var mouseY = 0.0;
//We need this to get a random place for the balls
var random = new java.util.Random();
//state of the game 1 is “running” 2 is “game over”
var state = 1;
//not used at the moment
var counter = 0;
//player time
var currentRuntime: Number = 0;


//create a background and track mouse movements on it
def background = Rectangle {
            x: 0 y: 0 width: APP_WIDTH
            height: APP_HEIGHT
            fill: Color.web("#E6E6E6");
            onMouseMoved: function(e: MouseEvent) {
                mouseX = e.x;
                mouseY = e.y;
            }

        }

 //create player 
def player = Rectangle {
            x: bind mouseX - 10
            y: bind mouseY - 10
            width: 20
            height: 20
 //create a nice visual effect
            effect: InnerShadow {
                choke: 0.2
                offsetX: 1
                offsetY: 1
                radius: 5
                color: Color.WHITE
            }
        }

//create balls
var AIs: Ball[];
for (i in [0..16]) {
    insert Ball {
        //set balls to a random place
        x: random.nextInt(450), y: random.nextInt(450)
       //create a nice visual effect for the balls
        effect: InnerShadow {
            choke: 0.5
            offsetX: 1
            offsetY: 1
            radius: 5
            color: Color.BLACK
        };


    } into AIs;

    //let the balls go to random directions
    if(random.nextInt(100) mod 2 == 0){
        AIs[i].vy = 1
    }
    if(random.nextInt(100) mod 2 == 0){
        AIs[i].vx = -1
    }

}

//t1 is for game logic
def t1 = Timeline {
            repeatCount: Timeline.INDEFINITE
            keyFrames: [
                KeyFrame {
//17ms is better than 25…
                    time: 17ms //25ms
                    values: []
                    action: function() {
                        for (AI in AIs) {
                            //bounce from walls
                            if (AI.x + AI.vx < AI.radius) { AI.vx = -AI.vx;
                            }
                            if (AI.x + AI.vx > APP_WIDTH - 7) { AI.vx = -AI.vx;
                            }

                            if (AI.y + AI.vy < AI.radius) { AI.vy = -AI.vy;
                            }
                            if (AI.y + AI.vy > APP_WIDTH - 7) { AI.vy = -AI.vy
                            }

                            //bounce from other balls
                            /*
                            *not yet implemented
                            */

                            
                            //detect collissions
                            if (AI.x >= mouseX and AI.x <= mouseX + 10) {
                                if (AI.y + AI.radius >= mouseY - 10 and AI.y - AI.radius <= mouseY) {
                                    AI.vy = -AI.vy;
                                    state = 2;
                                }
                            } else if (AI.y >= mouseY - 10 and AI.y <= mouseY) {
                                if (AI.x + AI.radius >= mouseX and AI.x - AI.radius <= mouseX + 10) {
                                    AI.vx = -AI.vx;
                                    state = 2;

                                }
                            }

                            //calculate new position
                            AI.x += AI.vx;
                            AI.y += AI.vy;

                            //increase speed
                            AI.vx = AI.vx * 1.002;
                            AI.vy = AI.vy * 1.002;

                        }
                       // not used at the moment
                        counter++;
                    }
                }
            ]
        };
        //t1 observes the game state and reacts on it
def t2 = Timeline {
            repeatCount: Timeline.INDEFINITE
            keyFrames: [
                KeyFrame {
                    time: 25ms
                    values: []
                    action: function() {
                        /* insert Ball {
                        x: random.nextInt(500), y: random.nextInt(500)
                        } into AIs;*/
                        //insert AIs into stage.scene.content;


                        //stage.scene.impl_setStage(stage);
                        if (state != 1) {
                            t1.stop();
                            tlTimer.stop();
                            gameOverScreen.visible = true;

                        }
                    }
                }
            ]
        };
        //tlTimer is for displaying the current time
def tlTimer = Timeline {
            repeatCount: Timeline.INDEFINITE
            keyFrames: [
                KeyFrame {
                    time: 100ms
                    values: []
                    action: function() {
                        currentRuntime += 0.1;

                    }
                }
            ]
        };
//start all timers
tlTimer.play();
t1.play();
t2.play();

//create the text object for timer
def timer = Flow {
            content: [Text { content: bind currentRuntime.toString()
                    font: Font { size: 30 } }
            ];
        }

        //create the game over screen
var gameOverScreen: Group = Group {
            visible: false
            var r: Rectangle = Rectangle {
                        arcWidth: APP_WIDTH arcHeight: APP_WIDTH
                        width: APP_WIDTH, height: APP_WIDTH
                        fill: Color.ROSYBROWN
                        stroke: Color.DARKRED
                        strokeWidth: APP_WIDTH
                    }
            content: [
                r,
                Text {
                    font: Font {
                        size: 28
                    }
                    x: 20, y: 50
                    content: "Game Over! Time: ";
                },
                Text {
                    font: Font {
                        size: 28
                    }
                    x: 20, y: 80
                    content: bind String.valueOf(currentRuntime).concat(" Seconds")
                },
                Text {
                    font: Font {
                        size: 28
                    }
                    x: 20, y: 200
                    content: "By Benny Gächter ";
                },
                Hyperlink {
                    layoutX: 100,
                    layoutY: 230,
                    scaleX:3
                    scaleY:3
                    text: "www.bgaechter.ch"
                    action: function(): Void {
                        AppletStageExtension.showDocument("http://www.bgaechter.ch");
                    }
                }

                Button {
                    layoutX: 250
                    layoutY: 120
                    scaleX: 3
                    scaleY: 3
                    text: "Restart"
                    action: function() {
                        restart();

                    },
                }
            ]

        }
// Display everything
var stage: Stage = Stage {
            title: "Test App"
            width: 500
            height: 500

            scene: Scene {
                content: [
                    background,
                    player,
                    AIs,
                    timer,
                    gameOverScreen
                ]
            }
        }

//the ball class derived from CustomNode
class Ball extends CustomNode {
    // Ball position
    public var x: Number = 100;
    public var y: Number = 100;
    // Ball radius
    public var radius: Number = 10;
    // Ball velocity vectors
    public var vx: Number = 1.0;
    public var vy: Number = -1.0;

    public override function create(): Node {
        return Circle {
                    transforms: Translate { x: bind x, y: bind y }
                    radius: bind radius
                    fill: Color.RED
                }
    }

}
//The restart function, may be called after game over
function restart(): Void {
    state = 1;
    currentRuntime = 0;
    t1.playFromStart();
    tlTimer.playFromStart();
    gameOverScreen.visible = false;
    for (AI in AIs) {
        AI.vx = 1;
        AI.vy = -1;
    }
}