using JFrame with KeyListener Interface and using paint method

[Raviteja Penki]

hi,

i am trying to write a program
aim: generate an image by extending JFrame and by implementing KeyListener
i want to change the position of the image by pressing the keys -,=
i am unable to get the output.

verify this once and tell me the root cause

here i am attaching the code

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;

import javax.swing.JFrame;

import java.awt.Toolkit;

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.geom.AffineTransform;

import java.net.URL;
import java.util.*;

public class DrawImage extends JFrame implements KeyListener{
	
	private Image image;
	private Graphics2D g2d;
	
	
	public static void main(String[] args)
	{
		JFrame jf = new DrawImage();
		jf.setFocusable(true);
		jf.setVisible(true);
		
		
	}
	DrawImage()
	{
		super("DrawImage");
		
		setSize(600,500);
		setVisible(true);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		Toolkit tk = Toolkit.getDefaultToolkit();
		image = tk.getImage(getURL("small.png"));
		addKeyListener(this);
	}
	public URL getURL(String fileName)
	{
		URL url = null;
		try{
			url = this.getClass().getResource(fileName);
		}
		catch(Exception e){}
		return url;
	}
	public void paint(Graphics g)
	{
		g2d = (Graphics2D)g;
				
		g2d.setColor(Color.white);
		g2d.fillRect(0, 0, getSize().width, getSize().height);
		g2d.drawImage(image,0,40,this);	
		
	}
	public void keyPressed(KeyEvent ke){
		switch (ke.getKeyCode()) {
		case KeyEvent.VK_EQUALS:
			System.out.println("= pressed");
			g2d.setBackground(Color.WHITE);
			g2d.drawString("its working for =", 40, 40);
			g2d.drawImage(image, 40,40,this);
			
			break;
		case KeyEvent.VK_MINUS:
			System.out.println("- pressed");
			g2d.setBackground(Color.PINK);
			g2d.drawString("its working for -", 20, 20);
			g2d.drawImage(image, 20,20,this);
			
			 break;
		default:
			break;
		}
	}	
	public void keyReleased(KeyEvent ke){}
	public void keyTyped(KeyEvent ke){}
	
}

[Raviteja Penki]

its only printing the - pressed or = pressed
but its not doing any graphical thing on the JFrame window like changing the back ground color moving the image to that positions
not even printing the string

[Rob Spoor]

I'll move this to our GUI forum. And please UseCodeTags next time.

[Rob Camick]

Don't use KeyListeners. They only work when the component has focus. Intead you should be using Key Bindings.

Don't override the paint() method of a JFrame. Instead read the section from the Swing tutorial on Custom Painting for the proper way to do this.

[Ranganathan Kaliyur Mannar]

Also, you are storing the Graphics object and making changes to that from the keyListener methods. I am not sure if the same graphics object is passed to the paint methods. Instead, you can store the key event generated in an instance variable (in the key listener methods) and make a call to repaint(). Then in the paintComponent method, you have to do the if/switch check and draw the graph accordingly.