java won't listen for key and action events and i have no clue why...?

Question

when i run the following program, it listens to the buttons
but clicking the keys does nothing? why?


import javax.swing.*;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.*;



public class KeyBoardTest extends JApplet implements KeyListener, ActionListener
{
private String event = " "; // description of keyboard event

private int xcoordinate = 400; // starting xcoordinate of the message
private int ycoordinate = 300; // starting ycoordinate of the event
private int increment = 20; // int to increment location upon keyboard events

private JButton topButton; // button to reset location to the top
private JButton centerButton; // button to reset location to the center

@Override
public void init() // set up GUI
{
setLayout(new FlowLayout()); // set the layout of the applet
setSize(800, 600); // set the size of the applet
addKeyListener(this); // listen for keyboard events

centerButton = new JButton("Reset to Center :"); // set up Center button
centerButton.addActionListener(this);
add(centerButton);

topButton = new JButton("Reset to Top Left :"); // set up Top Left button
topButton.addActionListener(this);
add(topButton);

event = "You are at (" + xcoordinate + ", " + ycoordinate + ") ";
}

@Override
public void paint(Graphics g)
{
super.paint(g);

g.drawString(event, xcoordinate, ycoordinate); // draw messgae to the applet
}

public void keyPressed(KeyEvent e) // handle key presses
{
}

public void keyReleased(KeyEvent e) // handle key releases
{
}

public void keyTyped(KeyEvent e) // handle typing on applet
{

if (e.getKeyChar() == 'h') // when 'h' key is pressed
{
ycoordinate = ycoordinate + increment;
}
if (e.getKeyChar() == 'j') // when 'j' key is pressed
{
ycoordinate = ycoordinate - increment;
}
if (e.getKeyChar() == 'k') // when 'k' key is pressed
{
xcoordinate = xcoordinate - increment;
}
if (e.getKeyChar() == 'l') // when 'l' key is pressed
{
xcoordinate = xcoordinate + increment;
}

event = "You are at (" + xcoordinate + ", " + ycoordinate + ") ";

repaint();
}

public void actionPerformed(ActionEvent e) // handle button clicks
{
if(e.getSource() == topButton) // process clicking "Center" button
{
xcoordinate = 10; // reset the xcoordinate
ycoordinate = 50; // reset the ycoordinate
}
if(e.getSource() == centerButton) // process clicking "Clear" button
{
xcoordinate = 400; // reset the xcoordinate
ycoordinate = 300; // reset the ycoordinate
}

event = "You are at (" + xcoordinate + ", " + ycoordinate + ") ";

requestFocus();
repaint();


}
}

Answer 1

The movement keys (j,h,k,l) work here as long as:

a) The applet has focus

b) The buttons do not have focus.



Solutions:

a) Make sure the applet has focus.

b) Either add the KeyListener to the buttons as well, or add KeyBindings to the lot.



As an aside. I usually do not post to Yahoo forums. For best answers on Java & applets, I would recommend either the Oracle forums or StackOverflow.

Answer 2

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Answer 5

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