help why doesn't my program work

[Ray]

import java.awt.Color;
import java.awt.*;
import java.awt.event.MouseListener;
import javax.swing.*;
import java.awt.Graphics;
import java.awt.Shape;
import java.awt.Graphics2D;
import java.awt.event.MouseEvent;
import java.awt.Dimension;
import java.awt.Paint;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.Rectangle;

public class MouseTracker extends JPanel implements MouseListener {

private JPanel p;
private JFrame f;
private Rectangle square;

public void run( )
{
f = new JFrame( "Graphics" );
f.setSize( 500, 500 );
f.setVisible( true );



// adding event listener using inner class
f.addWindowListener( new WindowAdapter( )
{
public void windowClosing( WindowEvent e )
{
System.exit( 0 );
}
});


p = new JPanel( );
p.setSize(500,500);
f.setContentPane( p );
p.addMouseListener(this);

}



// MouseListener event handlers
public void mouseClicked( MouseEvent e )
{

int x = e.getX();
int y = e.getY();

Graphics g = this.getGraphics();

Graphics2D g2 = (Graphics2D)g;


if (e.isMetaDown())
{
p.getContentPane().add(square);

square = new Rectangle(20,20);

square.setLocation(x, y);

g2.draw(square);


}
else
{
g2.drawOval(x, y, 20, 20);
//p.repaint();
}
}

public void mousePressed( MouseEvent e ){}
public void mouseReleased( MouseEvent e ){}

public void mouseEntered( MouseEvent e )
{
p.setBackground(Color.pink);
p.repaint();
}

public void mouseExited( MouseEvent e )
{
p.setBackground(Color.lightGray);
p.repaint();
}

public void paintComponent(Graphics g)
{
super.paintComponent(g);

}

public static void main( String args[] )
{
MouseTracker app = new MouseTracker();

app.run();
}
}

[Kent]

Firstly, your question should be "why doesn't my program compile?"

The answer is because of this line:

p.getContentPane().add(square);

You're trying to add a non-component (Rectangle) to a container.


Secondly, you're trying to draw on a panel in a mouse event. You need to
do this in the paint() method for the panel.

Take a look at this and see if it makes sense. If not, post again:




/////////////////////////
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class MouseTracker extends JFrame {
public static void main(String[] args) {
MouseTracker mt = new MouseTracker();
mt.setVisible(true);
}

public MouseTracker() {
this.getContentPane().add(new MouseTrackerPanel());
this.addMouseListener(new MyMouseListener());
this.pack();
this.setSize(300,300);
}

private class MouseTrackerPanel extends JPanel {
public MouseTrackerPanel() {
}

public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;

if (MouseTracker.this.x != -1) {
Rectangle r = new Rectangle(10, 10);
r.setLocation(x, y);
g2d.draw(r);
}
}
}

private class MyMouseListener extends MouseAdapter {
public void mouseClicked(MouseEvent e) {
MouseTracker.this.x = e.getX();
MouseTracker.this.y = e.getY();
MouseTracker.this.repaint();
}
}

private int x = -1;
private int y = -1;
}
////////////////

Regards,
Kent











"Ray" <figueror@fiu.edu> wrote:
>
>import java.awt.Color;
>import java.awt.*;
>import java.awt.event.MouseListener;
>import javax.swing.*;
>import java.awt.Graphics;
>import java.awt.Shape;
>import java.awt.Graphics2D;
>import java.awt.event.MouseEvent;
>import java.awt.Dimension;
>import java.awt.Paint;
>import java.awt.event.WindowAdapter;
>import java.awt.event.WindowEvent;
>import java.awt.Rectangle;
>
>public class MouseTracker extends JPanel implements MouseListener {
>
> private JPanel p;
> private JFrame f;
> private Rectangle square;
>
> public void run( )
> {
> f = new JFrame( "Graphics" );
> f.setSize( 500, 500 );
> f.setVisible( true );
>
>
>
> // adding event listener using inner class
> f.addWindowListener( new WindowAdapter( )
> {
> public void windowClosing( WindowEvent e )
> {
> System.exit( 0 );
> }
> });
>
>
> p = new JPanel( );
> p.setSize(500,500);
> f.setContentPane( p );
> p.addMouseListener(this);
>
> }
>
>
>
> // MouseListener event handlers
> public void mouseClicked( MouseEvent e )
> {
>
> int x = e.getX();
> int y = e.getY();
>
> Graphics g = this.getGraphics();
>
> Graphics2D g2 = (Graphics2D)g;
>
>
> if (e.isMetaDown())
> {
> p.getContentPane().add(square);
>
> square = new Rectangle(20,20);
>
> square.setLocation(x, y);
>
> g2.draw(square);
>
>
> }
> else
> {
> g2.drawOval(x, y, 20, 20);
> //p.repaint();
> }
> }
>
> public void mousePressed( MouseEvent e ){}
> public void mouseReleased( MouseEvent e ){}
>
> public void mouseEntered( MouseEvent e )
> {
> p.setBackground(Color.pink);
> p.repaint();
> }
>
> public void mouseExited( MouseEvent e )
> {
> p.setBackground(Color.lightGray);
> p.repaint();
> }
>
> public void paintComponent(Graphics g)
> {
> super.paintComponent(g);
>
> }
>
> public static void main( String args[] )
> {
> MouseTracker app = new MouseTracker();
>
> app.run();
> }
>}
>
>