Skip to content

Month: October 2008

JavaFX, rectangular collision detection


In a game I wrote some years ago we handled simple rectangular collisions. Given the points:

We did:

// returning 0 means collision
int collision(int ax, int ay, int bx, int by, int cx, int cy, int dx, int dy){
	return ((ax > dx)||(bx < cx)||(ay > dy)||(by < cy));

I'll show here a little demo about how implement simple rectangular collisions on JavaFX.
First I created a movable rectangle using the same idea of draggable nodes I already had posted before.

import javafx.input.MouseEvent;
import javafx.scene.geometry.Rectangle;

public class MovableRectangle extends Rectangle {
    private attribute startX = 0.0;
    private attribute startY = 0.0;

    public attribute onMove = function(e:MouseEvent):Void {}

    override attribute onMousePressed = function(e:MouseEvent):Void {
        startX = e.getDragX()-translateX;
        startY = e.getDragY()-translateY;

    override attribute onMouseDragged = function(e:MouseEvent):Void {
        translateX = e.getDragX()-startX;
        translateY = e.getDragY()-startY;

In the main code I some important things:

  • colide, a color that represents the collision effect. White means no collision and gray means collision.
  • rec1 and rec2, the two rectangles that can collide.
  • checkcollision() the function that checks and handles a possible collision.

Here is the main code:

import javafx.application.Frame;
import javafx.application.Stage;
import javafx.scene.geometry.Rectangle;
import javafx.scene.paint.Color;
import javafx.input.MouseEvent;

var colide = Color.WHITE;

function checkcollision():Void {
    if (
        (rec1.getBoundsX() > rec2.getBoundsX() + rec2.getWidth()) or
        (rec1.getBoundsX() + rec1.getWidth() < rec2.getBoundsX()) or 
        (rec1.getBoundsY() > rec2.getBoundsY() + rec2.getHeight()) or 
        (rec1.getBoundsY() + rec1.getHeight() < rec2.getBoundsY())
    ) {
        colide = Color.WHITE
    } else {
        colide = Color.LIGHTGRAY

var rec1: MovableRectangle = MovableRectangle {
    x: 10, y: 10, width: 50, height: 60, fill: Color.RED
    onMove: function(e:MouseEvent):Void {

var rec2: MovableRectangle = MovableRectangle {
    x: 100, y: 100, width: 70, height: 30, fill: Color.BLUE
    onMove: function(MouseEvent):Void {
Frame {
    title: "Rectangular Collisions", width: 300, height: 300
    closeAction: function() { 
        java.lang.System.exit( 0 ); 
    visible: true

    stage: Stage {
        fill: bind colide
        content: [rec1, rec2]

Try it via Java Web Start:

Java Web Start

Some considerations:

  • You can use rectangular collisions to create bounding boxes to handle collisions in more complex shapes or sprites. Is a common approach in 2d games to avoid more expensive calculations.
  • There are space for optimizations.
  • In this case I'm using only two objects. Some problems raises when I have N objects to handle.

More generally, we can code:

function collission(ax, ay, bx, by, cx, cy, dx, dy): Boolean {
    return not ((ax > dx)or(bx < cx)or(ay > dy)or(by < cy));

function hitnode(a: Node, b:Node): Boolean{
    return (collission(
        a.getBoundsX(), a.getBoundsY(),
        a.getBoundsX() + a.getWidth(), a.getBoundsY() + a.getHeight(),
        b.getX(), b.getY(),
        b.getX() + b.getWidth(), b.getY() + b.getHeight()

This way we can pass just two bounding boxes to hitnode and easily check collision of a node against a list of bounding boxes nodes.
Using the same approach I also wrote this function to test if a Node is inside another Node:

function inside (ax, ay, bx, by, cx, cy, dx, dy):Boolean{
    return ((ax > cx) and (bx < dx) and (ay > cy) and (by < dy));

function insidenode(a:Node,b:Node):Boolean{
    return (inside(
        a.getBoundsX(), a.getBoundsY(),
        a.getBoundsX() + a.getWidth(), a.getBoundsY() + a.getHeight(),
        b.getBoundsX(), b.getBoundsY(),
        b.getBoundsX() + b.getWidth(), b.getBoundsY() + b.getHeight()

Soon I'll post game examples showing how to use this method and others collission detection methods.


Ainda essa semana

Ainda essa semana eu vou fazer três palestras. Olhe aí se você não vai estar por perto. 😉

  • 29/10 – Quarta-feira 20:30 – Palestra sobre NetBeans no na VII Semana de TI e Telecomunicações da FIC.
  • 30/10 – Sexta-feira 09:30 – Palestra sobre OpenSolaris também na VII Semana de TI e Telecomunicações da FIC.
  • 01/11Sábado 15:20 – Palestra Apresentando o CEJUG e o poder do Java em Iguatu no Encontro PHP & Java.

SCSNI Study Guide

This is a draft of study guide based on SCSNI (Sun Certified Specialist Netbeans IDE) exam objectives.

SCSNI Study Guide
Exam Objetive Resources
Section 1: IDE Configuration
1.1 Demonstrate the ability to configure the functionality available in the IDE, including using enabling and disabling functionality and using the Plugin Manager.
1.2 Explain the purpose of the user directory and the netbeans.conf file and how these can be used to configure the IDE.
1.3 Demonstrate the ability to work with servers in the IDE, such as registering new server instances and stopping and starting servers.
1.4 Describe how to integrate external libraries in the IDE and use them in coding and debugging your project.
1.5 Demonstrate knowledge of working with databases in the IDE, including registering new database connections and tables running SQL scripts.
1.6 Describe how to integrate and use different versions of the JDK in the IDE for coding, debugging, and viewing Javadoc documentation.
Section 2: Project Setup
2.1 Describe the characteristics and uses of a free-form project.
2.2 Demonstrate the ability to work with version control systems and the IDE. (Which VCS’s are available, which ones you need an external client for, how to pull sources out of a repository, view changes, and check them back in).
2.3 Describe the ways in which you can change the build process for a standard project, such as configuring project properties and modifying the project’s Ant build script.
2.4 Configure your project to compile against and run on a specific version of the JDK.
Section 3: Java SE Development
3.1 Demonstrate the ability to create NetBeans projects from the source code of an existing Java SE program.
3.2 Describe how to manage the classpath of a Java SE project, including maintaining a separate classpath for compiling and debugging.
3.3 Demonstrate the knowledge of the NetBeans GUI Builder and the ability to lay out and hook up basic forms using it.
3.4 Demonstrate the ability to package and distribute a built Java Desktop project for use by another user.
Section 4: Java EE Web Development
4.1 Describe how to create a NetBeans project from the source code of an existing Web application.
4.2 Distinguish between a visual web application and web application.
4.3 Demonstrate knowledge of which web frameworks are available in NetBeans IDE and how they are added to and used in a web application.
4.4 Describe how to monitor HTTP requests when running a web application.
4.5 Demonstrate a knowledge of basic tasks related to building and deploying web applications to a server, such as changing the target server and undeploying an application.
Section 5: Editing
5.1 Describe the purpose and uses of refactoring and demonstrate the ability to perform basic refactoring on Java source code.
5.2 Describe how to use the Options window to change the default appearance and behavior of the Source Editor.
5.3 Describe the ways that the IDE highlights errors in source code and the tools the IDE offers for correcting those errors.
5.4 Demonstrate the ability to use editor hints, such as implementing all the methods for an implemented interface
5.5 Demonstrate the ability to use live code templates such as automatic generation of constructors, try/catch loops, and getters and setters.
Section 6: Testing, Profiling, and Debugging
6.1 Demonstrate the ability to work with JUnit tests in the IDE, such as creating JUnit tests and interpreting JUnit test output.
6.2 Describe how to debug a local (desktop) application, including setting breakpoints and stepping through code.
6.3 Describe the difference between local and remote debugging and describe how to debug a remote (web) application.
6.4 Describe the purpose of profiling applications and how to profile a local desktop application in the IDE.

More useful resources:

Please, collaborate in the comments with others resource links (with section number). Let’s complete this guide.

Short urls with Glassfish+MySQL

Pipes, Creative Commons photo by flattop341.

1. The Problem

Internet is full of long urls and meaningless.

Long urls are difficult to remember or print, usually full of redundancy and low semantic. With short and meaningful urls you can avoid thes problems and even achieve profitable goals with SEO
SEO (search engine optimization) technics.

There are services like Tiny URL, Fancy URL, Moo URL and others. Although they solve part of the problems, they bring several others. Another problem is if you have a web site like and use a third-party service for short urls you are losing part of your mind-share with your users and clients.

As an example, if a company wants to promote a open work position would be preferable spread a instead of a, or even worst, a (meaningless hash).

2. Solution Approach

I created a little program called xort that can be placed on your own server and provide you own short maintening your base url.

I use a pipe abstraction. Each pipe redirects from a key url to an output url.

The idea is that you have xort installed and associated into your domain (preferably on /x). A pipe inside would be like

3. Tools

All those tools are multi platform, open source and free.

3.1 Glassfish Application Server

Glassfish is an open source application server project led by Sun Microsystems for the Java Enterprise Edition (Java EE) platform. It’s very easy to install and run and have a very nice administration web interface where you can do from simple tasks like deploy a application to more complexes like clustering.

Glassfish Admin Console

To develop the application I’m using NetBeans 6.5 Beta that comes with Glassfish V3 prelude b15b. Netbeans also provides a integration of project, database and web server.

Nevertheless, Glassfish has no dependencies with any IDE and perfectly works by alone. If you need I wrote this post explaining how to install and deploy a application on Glassfish from scratch.

3.2 MySQL Relational Database

MySQL is a relational database management system and probably the most used database on internet (has more than 11 million installations). It’s also very easy to install and administer, through command line or many gui interfaces.

To install MySQL and JDBC driver on Ubuntu just run as root:

# apt-get install mysql-server libmysql-java

After installing and configuring it you can test the jdbc driver throught this servlet code. You can optionally register the MySQL on NetBeans to have a easier access to it thought the service tab.

At the command line you can invoke mysql command line interface and use MySql commands or SQL queries. I’ll login and create a database called xort:

$ mysql -u username -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.0.51a-3ubuntu5.3 (Ubuntu)

Type ‘help;’ or ‘\h’ for help. Type ‘\c’ to clear the buffer.

mysql> create database xort;
Query OK, 1 row affected (0.06 sec)

You could also create this database by an SQL statement:


To select the database xort:

mysql> use xort;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

Now we create a database called pipes with fields pin (pipe in) and pout (pipe out). They represent the input url and the output url of our pipe abstraction.

   pin varchar(255) NOT NULL,
   pout varchar(255)

As we expect a lot of searches queries on this table, we can optionally create a index for it on pin field. This can reduce ours searches from O(n) to O(logn) (because pin’s will be ordered so don’t need to look all pipes, we can use logn algorithms like binary search).

CREATE INDEX pinindex ON pipes (pin);

Another trick to improve our speed is recycling connections through connection pools.

Creating a pool of MySQL connections on Glassfish is very easy. There’re two good tutorials on this subject:

And now we populate the database with some initial pipes.

INSERT INTO pipes VALUES ('blog','');
INSERT INTO pipes VALUES ('cejug','');
INSERT INTO pipes VALUES ('orkut','');
INSERT INTO pipes VALUES ('glassfish','');
INSERT INTO pipes VALUES ('mysql','');
INSERT INTO pipes VALUES ('twitter','');
INSERT INTO pipes VALUES ('lab', ',+Brazil&ie=UTF8&t=h&ll=-3.745978,-38.574023&spn=0.002452,0.004823&z=18');
INSERT INTO pipes VALUES ('videos', '');
INSERT INTO pipes VALUES ('photos', '');

4. Program

Basically we have just a program that implement this simple behavior:

  1. separate the key from the url.
  2. if the key is a pin from a pipe then redirect to that pout.
  3. else provide a way to create a new pipe.
  4. list all pipes.
  5. provide a way to remove a pipe.

To get the key we need to separate the proper part of the request uri:

String uri = request.getRequestURI();
String key = uri.substring(request.getContextPath().length()+1);

After that we check if it matches with a pin of some pipe. In this case we redirect user for the correspondent pout:


Notice that using this approach we can connect a url to a extern or intern url (even to another pipe).

5. Download

Check out the xort project and sources at

Or grab sources and the current build with:

svn checkout xort

Parameters can be passed by the the web.xml file:

   Set if users can add new pipes using the web interface.

   JDBC driver to use

   Username to login on the database.

   Password for the given username.

   JDBC path to database.

Xort up and running:


JavaFX Overview Slides

My slides about a overview on JavaFX at our last CEJUG event.

JavaFX Overview

View SlideShare presentation or Upload your own. (tags: javafx ria)


Café com Tapioca na Christus

Café com Tapioca na Christus

Here a little screncast showing the live preview feature on the NetBeans JavaFX Plugin.


You can also download the orignal screencast in higher resolution netbeans_javafx_preview.ogg (15 Mb). Photos of the presentation at my Flickr album.



A new toy in my desk. One of many I gave myself in the children’s day this year.

Put on your sunday clothes!