Re: need help or explanation
In article <jLGdnTFE1sd696zWnZ2dnUVZ_qmdnZ2d@posted.oberlin>,
"Dave" <none123@none456.net> wrote:
I'm new to Java and I'm running into a problem I can't figure out.
I have a menu on a screen and I'm also drawing a moving filled oval
on it.
When I run the program, I end up with a double menu line. It's as if
the first repaint is shifting the whole display down the size of the
menu line. The first oval is also shifted down the size of the menu
line. The rest of the oval repaints seem to be where they should be.
Even though I have 2 menu lines, only the top menu works when I click
on it. When I click on "Menu1", I get 2 "first entry" items, one
below the other. See Menu example below.
------------------------------------------------
Menu1 (this menu works when I click on it)
------------------------------------------------
Menu1 (this menu doesn't do anything)
------------------------------------------------
-----------------------------------------------------------
Menu1 (when I click the top menu, I get 2 first entries)
-----------------------------------------------------------
first entry (the lower Menu1 is written over)
-----------------------------------------------------------
first entry
-----------------------------------------------------------
The bad part is, when I run this program at work, it works like it's
supposed to. When I run it at home, I get the double menu. I haven't
tried the program on any other PC's yet.
First, you need to construct your GUI on the Even Dispatch Thread (EDT),
otherwise your program may exhibit various such anomalies on different
platforms:
<http://java.sun.com/docs/books/tutorial/uiswing/concurrency/initial.html>
Having done that, you must not then block the EDT with time-consuming
operations. Here's a modified version of your program that uses a Swing
Timer to periodically repaint the panel:
package news;
import java.awt.event.ActionEvent;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
public class Graph1 extends JFrame implements ActionListener {
private final Timer timer = new Timer(200, this);
private final MyPaint mp = new MyPaint();
private int x = 70;
private int y = 70;
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new Graph1();
}
});
}
public Graph1() {
super("Graph1");
JMenuBar mBar = new JMenuBar();
JMenu mMenu1 = new JMenu("Menu1");
JMenuItem mItem = new JMenuItem("first entry");
mBar.add(mMenu1);
mMenu1.add(mItem);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setJMenuBar(mBar);
this.add(mp);
this.pack();
this.setVisible(true);
timer.start();
}
@Override
public void actionPerformed(ActionEvent e) {
x++; y ++;
mp.repaint();
}
private class MyPaint extends JPanel {
public MyPaint() {
this.setPreferredSize(new Dimension (600, 600));
}
@Override
public void paintComponent(Graphics g) {
g.setColor(Color.green);
g.fillOval(x, y, 40, 40);
}
}
}
See also, <http://zetcode.com/tutorials/javagamestutorial/>
--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>