AffineTransform doesn't move image on key presses

Question

I'm having a bit of trouble developing my first Java game using images instead of vector graphics. Currently I'm experimenting with moving an Image on a key press with the AffineTransform object. Only it won't move. What am I doing wrong? I haven't tried using threads yet, but I am not sure how to do this. If you think it would help, please include it in your answer.

Here is my code:

import java.awt.*;
import java.net.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.applet.*;
public class DisplayImage extends Applet implements KeyListener{
    AffineTransform identity = new AffineTransform();
    boolean left = false;
    boolean right = false;
    public URL getURL(String filename)
    {
        URL url = null;
        try
        {
            url = this.getClass().getResource(filename);
        }
        catch(Exception e){e.printStackTrace();}
        return url;
    }
    private Image image;
    public void init()
    {
        image = getImage(getURL("spaceship.png"));
        addKeyListener(this);
    }
    public void update(Graphics g){paint(g);}
    public void paint(Graphics g)
    {
        AffineTransform trans = new AffineTransform();
        trans.setTransform(identity);

        Graphics2D g2d = (Graphics2D)g;
        g2d.setColor(Color.BLACK);
        g2d.fillRect(0,0,getSize().width,getSize().height);

        if(left==true)
        {
            trans.translate(-10,0);
            left = false;
            repaint();
        }
        if(right==true)
        {
            trans.translate(10,0);
            right = false;
            repaint();
        }
        g2d.drawImage(image,0,0,this);
    }
    public void keyPressed(KeyEvent e)
    {
        int keycode = e.getKeyCode();
        switch(keycode)
        {
        case KeyEvent.VK_RIGHT:
            right = true;
            repaint();
        case KeyEvent.VK_LEFT:
            left = true;
            repaint();
        }
    }
    public void keyTyped(KeyEvent e){}
    public void keyReleased(KeyEvent e){}

}

Can someone please comment or answer? I feel a "tumbleweed" badge heading my way.

Answer 1

Overall, the approach you're learning from your book is far from ideal for games but I touched up the code anyway.

import java.awt.*;
import java.net.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.applet.*;
public class DisplayImage extends Applet implements KeyListener{

 int coordX=0;//ship x axis position
 int coordY=0;//ship y axis position
 /*
  0-------------------------x
 0|
  |
  |
  |
  |
  |
  y
 */
public URL getURL(String filename)
{
    URL url = null;
    try
    {
        url = this.getClass().getResource(filename);
    }
    catch(Exception e){e.printStackTrace();}
    return url;
}
private Image image;
public void init()
{
    image = getImage(getURL("spaceship.png"));
    addKeyListener(this);
}
public void update(){repaint();}//let update control the calls to repaint
public void paint(Graphics g)
{

    Graphics2D g2d = (Graphics2D)g;
    g2d.setColor(Color.BLACK);
    g2d.fillRect(0,0,getSize().width,getSize().height);

    g2d.drawImage(image,coordX,coordY,this);//paint the spaceship to the updated coordinates
}
public void keyPressed(KeyEvent e)
{
    int keycode = e.getKeyCode();
    //37=left arrow. 39=right arrow. 38=up & 40=down
    if(keycode==37){coordX-=1;}else if(keycode==39){coordX+=1;}
    if(keycode==38){coordY-=1;}else if(keycode==40){coordY+=1;}

update();//request repaint when logic has updated
}
public void keyTyped(KeyEvent e){}
public void keyReleased(KeyEvent e){}

}

Cheers

EDIT:: This is the basic concept you want to work on.

private void mainGameLoop(){
 while(pause==false){
  updateLogic();//process movement, detect collisions etc
  renderGraphics();//draw a new frame
  try{Thread.sleep(25);}catch(InterruptedException e){e.printStackTrace();}//sleep the thread to control the frame rate. (there are more efficient ways to sleep a thread but this is the most simplistic)
 }
}