Thread: Why isn't this rectangle moving?

Ok so I am trying to make a galaga game and I'm not getting very far at all. I just tried to make a rectangle be the spaceship and have you able to move it left and right, but it won't work. I added a keylistener and told it to add 5 to x when right arrowkey is hit and subtract 5 from x when the left arrow key is hit but the rectangle doesn't move when I run this program! Here is my code of what I did:

package galaga;
 
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
 
import javax.swing.JFrame;
 
public class mainmethod extends JFrame{
	int x = 200, y= 300;
	KL bob = new KL();
	public mainmethod() {
		super("Galaga");
		setVisible(true);
		setLocation(150,150);
		setSize(400,400);
		addKeyListener(bob);
	}
 
	public class KL implements KeyListener{
 
 
		public void keyPressed(KeyEvent e) {
			if(e.getKeyCode() == KeyEvent.VK_LEFT) {
			x = x-5;
			}
			if(e.getKeyCode() == KeyEvent.VK_RIGHT) {
			x = x+5;
			}
		}
		public void keyReleased(KeyEvent e) {
 
 
		}
 
		@Override
		public void keyTyped(KeyEvent e) {
 
 
		}
	}
	public void paint(Graphics g) {
		Image dbImage = createImage(getWidth(), getHeight());
		Graphics dbGraphics = dbImage.getGraphics();
		paintComponent(dbGraphics);
		g.drawImage(dbImage, 0, 0, this);
		}
 
	public void paintComponent(Graphics g){
		g.setColor(Color.CYAN);
		Rectangle blarp = new Rectangle(x, y, 150, 150);
		g.fillRect((int) blarp.getX(), (int) blarp.getY(), 90, 50);
 
	}
 
 
 
 
 
 
 
 
 
 
}

Please help me and thanks if you take the time to read this

Originally Posted by mkrage

Why isn't this rectangle moving?

1. After changing x in the KeyListener routine you don't redraw(), so KeyListener has no effect on what you see.
   
   
2. x and y are not used in the drawImage method, so no matter what you do with the value of x, nothing changes. (Hint: give initial values of x and y so that the rectangle is somewhere within the frame. Then use x,y in drawImage)

Cheers!

Z

Also you don't want to draw directly into a JFrame. Instead draw in the paintComponent override method of a JPanel or other class derived from JComponent. Be sure to call the super method first. Finally, your KeyListener won't work if the component listened to doesn't have the focus. For Swing applications it's usually better to use Key Bindings and not KeyListeners.

Originally Posted by Zaphod_b

1. After changing x in the KeyListener routine you don't redraw(), so KeyListener has no effect on what you see.
   
   
2. x and y are not used in the drawImage method, so no matter what you do with the value of x, nothing changes. (Hint: give initial values of x and y so that the rectangle is somewhere within the frame. Then use x,y in drawImage)

Cheers!

Z

Ok for number 1 do i put repaint() (redraw() didnt work) inside the keylistener or where do i put it?
And for number 2 idk what u mean by initialize x. Does that just mean do x=150 in the paint or paintcomponent method. Sorry I do not understand your basic helpful message. I am still a beginner to programing and am not taking a class, i am just doing this on free time but thank you soooooooo much for trying to help!


-mkrage

Originally Posted by curmudgeon

Also you don't want to draw directly into a JFrame. Instead draw in the paintComponent override method of a JPanel or other class derived from JComponent. Be sure to call the super method first. Finally, your KeyListener won't work if the component listened to doesn't have the focus. For Swing applications it's usually better to use Key Bindings and not KeyListeners.

Ok first of all thank you for your help. Second its better if I draw on a JPanel an add it on and i am not familiar with key bindings and how they work! If you could tell a brief explanation on how they work and are set up and what parameter they take that would be much appreciated!

Thanks for your help

-mkrage

Yes thank you so much! I now have a moving rectangle! I now understand what you have to do to initialize and how you must use repaint! Thank you so much!