Tutorial - Writing a Space Invaders game in Java

Since we want to develop a somewhat interesting game, it is clear that we cannot paint our monsters and spaceships using the standard Java drawing primitives of Graphics2D (i.e. lines, points, and simple shapes). Instead we will use image files which we will load as we need them.

So our next step will be loading an external image and painting it on the window. As a starting point and in order to make use of transparency easy , we'll use .gif images, and we'll load them using the ImageIO class added in JDK 1.4.

The image we'll load is called bicho.gif and must be in a subdirectory called "res" (resources) beneath the main directory of our project (but not beneath the package directory). For example, if our class is located in c:\planetalia\curso\java\version04\Invaders.class, then the resource directory must be located in c:\planetalia\curso\java\res\):


1     package version04;
2     /**
3      * Curso B?sico de desarrollo de Juegos en Java - Invaders
4      * 
5      * (c) 2004 Planetalia S.L. - Todos los derechos reservados. Prohibida su reproducci?n
6      * 
7      * http://www.planetalia.com
8      * 
9      */
10    
11    
12    import java.awt.Canvas;
13    import java.awt.Dimension;
14    import java.awt.Graphics;
15    import java.awt.event.WindowAdapter;
16    import java.awt.event.WindowEvent;
17    import java.awt.image.BufferedImage;
18    import java.net.URL;
19    
20    import javax.imageio.ImageIO;
21    import javax.swing.JFrame;
22    import javax.swing.JPanel;
23    
24    public class Invaders extends Canvas {
25      public static final int WIDTH = 800;
26      public static final int HEIGHT = 600;
27      
28      
29      public Invaders() {
30        JFrame ventana = new JFrame("Invaders");
31        JPanel panel = (JPanel)ventana.getContentPane();
32        setBounds(0,0,WIDTH,HEIGHT);
33        panel.setPreferredSize(new Dimension(WIDTH,HEIGHT));
34        panel.setLayout(null);
35        panel.add(this);
36        ventana.setBounds(0,0,WIDTH,HEIGHT);
37        ventana.setVisible(true);
38        ventana.addWindowListener( new WindowAdapter() {
39          public void windowClosing(WindowEvent e) {
40            System.exit(0);
41          }
42        });
43      }
44      
45      public BufferedImage loadImage(String nombre) {

46        URL url=null;
47        try {
48          url = getClass().getClassLoader().getResource(nombre);
49          return ImageIO.read(url);
50        } catch (Exception e) {
51          System.out.println("No se pudo cargar la imagen " + nombre +" de "+url);
52          System.out.println("El error fue : "+e.getClass().getName()+" "+e.getMessage());
53          System.exit(0);
54          return null;
55        }
56      }
57      
58      

59      public void paint(Graphics g) {
60        BufferedImage bicho = loadImage("res/bicho.gif");

61        g.drawImage(bicho, 40, 40,this);

62      }
63      
64      public static void main(String[] args) {
65        Invaders inv = new Invaders();
66      }
67    }
68

You can see that error handling is almost nonexistent : Any problem during the loading of the image causes the program to stop. We'll try to improve this later on.

It's also interesting to point that instead of using a hand-coded path to the image, we use getClass().getClassLoader().getResource(...), which allows us to get a URL pointing to the folder from which our class was loaded. This allows us to move the program, or turn it into an applet, or deploy it using WebStart without having to change anything regarding the location of the images.

Previous Page - First attempts at painting	Current Page - 04 - First images	Next Page - Optimizing the loading of images
	Return to the index of free Java tutorials

bicho.gif	bicho0.gif	bicho1.gif	bicho2.gif
bombD.gif	bombDL.gif	bombDR.gif	bombL.gif
bombR.gif	bombU.gif	bombUL.gif	bombUR.gif
disparo.gif	disparo0.gif	disparo1.gif	disparo2.gif
explosion.wav	misil.gif	missile.wav	musica.wav
nave.gif	oceano.gif	photon.wav	test.gif
Thumbs.db

Previous Page - First attempts at painting	Current Page - 04 - First images	Next Page - Optimizing the loading of images
	Return to the index of free Java tutorials

Training and Consulting

Tutorial - Writing a Space Invaders game in Java

First images

Full list of Java source files for this step

Full list of resources

	Training and Consulting
	Home