Thread: How to fix this code?

Hi guys

I have 2 problems here:
1. Below code does not draw a black Polygon on the frame, only shows an empty Frame named "Poppy"
2. Once the frame shows, I can't close it by clicking "x" at the right top corner.

Does anyone know why?

Thanks heaps

package brainydraw;
 
import java.awt.*;
import java.awt.event.*;
 
public class OctagonDrag extends Frame implements MouseMotionListener
{
    private int[] x = {150, 175, 175, 150, 100, 75, 75, 100};
    private int[] y = {150, 175, 175, 150, 100, 75, 75, 100};
    private Polygon p = new Polygon(x, y, 8);
    private int oldx; //Saves previous Polygon position
    private int oldy;
    private Frame f;
 
    public void init()
    {
        f = new Frame("Poppy");
        f.setSize(300, 300);
        f.show();
        addMouseListener(new MousePressListener());
        addMouseMotionListener(this);
    }
 
    public void paint(Graphics g)
    {
        g.setColor(Color.black);g.fillPolygon(p); 
    }
 
    public void mouseMoved(MouseEvent event)
    {
    }
 
    public void mouseDragged(MouseEvent event)
    {
        int x = event.getX();
        int y = event.getY();
        if (p.contains(x, y))
        {
            p.translate(x - oldx, y - oldy);
            oldx = x;
            oldy = y;
            repaint();
        }
    }
 
    class MousePressListener extends MouseAdapter
    {
 
        public void mousePressed(MouseEvent event)
        {
 
            int x = event.getX();
            int y = event.getY();
            if (p.contains(x, y))
            {
                oldx = x;
                oldy = y;
            }
        }
    }
 
    class CloseWindow implements WindowListener
    {
        public void windowClosing(WindowEvent event)
        {
            System.exit(0);
        }
        public void windowOpened(WindowEvent event)
        {
        }
        public void windowClosed(WindowEvent event)
        {
        }
        public void windowIconified(WindowEvent event)
        {
        }
        public void windowActivated(WindowEvent event)
        {
        }
        public void windowDeactivated(WindowEvent event)
        {
        }
        public void windowDeiconified(WindowEvent event)
        {
        }
    }
 
    public static void main(String[] args)
    {
        OctagonDrag test = new OctagonDrag();
        test.init();
    }
}

First, I'd encourage you to use a JFrame rather than a Frame (see How to use JFrames). Second, show is deprecated. Use setVisible(true). Next, you shouldn't override the paint method, especially of the Frame itself. Create a JPanel, add it to the JFrame, and override the paintComponent method of the JPanel (see Performing Custom Painting)

A word of advice: if you really want members here to take interest in helping you, format your code according to convention. The creative indents, code lines starting with { etc have put me off even trying to read it.

So, without attempting to read your code, here are some of the most common mistakes.
-- not adding the component that does the custom painting to the visible component hierarchy
-- not using an appropriate layout manager and/or not ensuring an appropriate preferredSize, resulting in a component of default size (usually [0, 0])
-- not calling repaint() on the component that does the custom painting but on some other component

db

Hi db
I have modified it with adding component and repaint() into init() method, please see above new code, but it still doesn't make a difference.
Any more ideas?
Thanks heaps

Originally Posted by aussiemcgr

...
    MyPanel panel = new MyPanel();
        f.getContentPane().add(panel);
        repaint();
    }
 
    class MyPanel extends JPanel
    {
        public void paintComponent(Graphics g)
        {
            g.setColor(Color.black);g.fillPolygon(p);
        }
 
   }

To add to what Darryl.Burke said, when you make the call repaint();, you are calling the OctagonDrag's default repaint() method. For example, you are effectively saying this.repaint(). What you want to do is call the MyPanel's repaint() method. To do that, you need to say panel.repaint();.

Hi aussiemcgr
Thanks for your advice, I have changed repaint(); to panel.repaint();, then ran it, it still display exactly same as before: an empty frame and it can't be closed by pressing "x".
more ideas?

Are you reading the stack trace? Any exceptions? This is important information...on close look the variable 'f' is never initialized, and the program sequence sets the frame to visible then, when you try to call a function of f you should get a NullPointerException. A recipe for the behavior you have. In addition, show is deprecated: you should use setVisible.

Why does the class extend Frame? It's never used as a Frame.

db

Hi copeg
I just read a bit stack trace, then looked at the error I got, which is:

run:
Exception in thread "main" java.lang.NullPointerException
at brainydraw.OctagonDrag.init(OctagonDrag.java:24)
at brainydraw.OctagonDrag.main(OctagonDrag.java:103)

Line24 is f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); But why? Why?why ?
why can't 'f' get initialized? I declared it in "private JFrame f;" in line 17.
(You said show() is depreciated, but actually it works fine as it does make frame dispaly, so I didn't change that)

Guys, do I need something else to initialize "f"?

Originally Posted by ice

Hi copeg
I just read a bit stack trace, then looked at the error I got, which is:

Line24 is f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); But why? Why?why ?
why can't 'f' get initialized? I declared it in "private JFrame f;" in line 17.

You need to initialize the object: (see Creating Objects)

f = new JFrame();

(You said show() is depreciated, but actually it works fine as it does make frame dispaly, so I didn't change that)

Guys, do I need something else to initialize "f"?

It may work, but you should not rely on deprecated methods. There is a reason they are deprecated, and its better to adhere to documentation than find out the hard way why a method is deprecated.

Great, guys, thanks a lot, now I solved to close the frame, see below updated code. But that black Polygon is still not displayed, where is it?

package brainydraw;
 
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics;
import javax.swing.*;
import javax.swing.JFrame;
 
 
public class OctagonDrag extends JFrame implements MouseMotionListener
{
    private int[] x = {150, 175, 175, 150, 100, 75, 75, 100};
    private int[] y = {150, 175, 175, 150, 100, 75, 75, 100};
    private Polygon p = new Polygon(x, y, 8);
    private int oldx; //Saves previous Polygon position
    private int oldy;
    private JFrame f = new JFrame();
 
    public void init()
    {
        setTitle("Poppy");
        setSize(300, 300);
        setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addMouseListener(new MousePressListener());
        addMouseMotionListener(this);
        MyPanel panel = new MyPanel();
        f.getContentPane().add(panel);
        panel.repaint();
    }
 
    class MyPanel extends JPanel
    {
        public void paintComponent(Graphics g)
        {
            g.setColor(Color.black);g.fillPolygon(p);
        }
 
   }
 
    public void mouseMoved(MouseEvent event)
    {
    }
 
    public void mouseDragged(MouseEvent event)
    {
        int x = event.getX();
        int y = event.getY();
        if (p.contains(x, y))
        {
            p.translate(x - oldx, y - oldy);
            oldx = x;
            oldy = y;
            repaint();
        }
    }
 
    class MousePressListener extends MouseAdapter
    {
 
        public void mousePressed(MouseEvent event)
        {
 
            int x = event.getX();
            int y = event.getY();
            if (p.contains(x, y))
            {
                oldx = x;
                oldy = y;
            }
        }
    }
 
    class CloseWindow implements WindowListener
    {
        public void windowClosing(WindowEvent event)
        {
            System.exit(0);
        }
        public void windowOpened(WindowEvent event)
        {
        }
        public void windowClosed(WindowEvent event)
        {
        }
        public void windowIconified(WindowEvent event)
        {
        }
        public void windowActivated(WindowEvent event)
        {
        }
        public void windowDeactivated(WindowEvent event)
        {
        }
        public void windowDeiconified(WindowEvent event)
        {
        }
    }
 
    public static void main(String[] args)
    {
        OctagonDrag test = new OctagonDrag();
        test.init();
 
    }
}

You are adding components to the frame after it is realized (visible). Add things prior, in this example move the setVisible method to the last call in the init function (in which case repaint is not necessary). As Darryl.Burke noted, there isn't much reason to have your OctagonDrag class extend JFrame if it is not being used.

NOTE: I'm not trying to offend you, I'm trying to help you.

You should delete your current code, learn a little about Java swing/AWT, and try again.

Putting all of your project code into one file makes your code extremely unorganized. (illegible) I like to structure my projects with a main class, a gui class, and a device class. (Keyboard and Mouse)

//Main class
import javax.swing.*;
 
public class ProjectMain {
   public static void main(){
      JFrame f = new JFrame("Poppy");
      f.getContentPane().setPreferredSize(new Dimension(300,300));
      f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
      gui gui = new gui(); //This is the class that handles all the drawing
      devices dev = new devices(); //Mouse and Keyboard class
      gui.addMouseListener(dev); 
      gui.addMouseMotionListener(dev);
 
      f.add(gui);
      f.pack();
      f.setVisible(true);
 
   }
}

Now the GUI class

//GUI Class
import javax.swing.*;
import java.awt.*;
 
public class gui extends JPanel { //Since this class extends JPanel it can be added to your JFrame in the main
    private int[] x = {150, 175, 175, 150, 100, 75, 75, 100};
    private int[] y = {150, 175, 175, 150, 100, 75, 75, 100};
    private Polygon p = new Polygon(x, y, 8);
    private int oldx; //Saves previous Polygon position
    private int oldy;
 
 
   public void paintComponent(Graphics g) {
      g.setColor(Color.black);
      g.fillPolygon(p);
   }
}

Now the device class (Mouse and Keyboard)

//device class
import java.awt.event.*;
 
public class devices implements MouseListener, MouseMotionListener {
 
   //implementing the mouse clicking methods
   public void mousePressed(MouseEvent e){}
   public void mouseReleased(MouseEvent e){}
   public void mouseClicked(MouseEvent e){} //mousePressed is more reliable 
 
   //implementing the mouse motion methods
   public void mouseMoved(MouseEvent e){}
   public void mouseDragged(MouseEvent e){}
   public void mouseEntered(MouseEvent e){}
   public void mouseExited(MouseEvent e){}
 
}

This code isn't ment to work. You're going to have to add/make changes to it. The code is ment to show you a basic structure for an organized GUI project. Most likely Darryl.Burke and or Copeg are going to correct some of my mistakes, show you better methods, comment on the irony. (If I made mistakes on the Swing/AWT parts) Like I said before, this code is only for knowledge.

Hi brt93yoda

Thanks very much for sharing what you know. But the main problem still can't be solved - the black polygon is not shown.
Any ways to make it visible?

Thanks heaps

Originally Posted by ice

Hi brt93yoda

Thanks very much for sharing what you know. But the main problem still can't be solved - the black polygon is not shown.
Any ways to make it visible?

It doesn't work because it only partially implements my suggestion from above. There are 2 setVisible calls...

Hi copeg
Sorry, that extra setVisible was there by accident, now I removed it. Actually I fully implented your suggestionn when I ran it, but the black polygon is really not shown.

hi guys, the problem is still not solved, anyone got more ideas?

Can you post a short compilable example of the code to this point that demonstrates the problem? With all these posts its hard to be sure where the code stands at this point.

Ok, copeg, I am not sure which part of the code that causes the problem - it doesn't draw polygon. Here is the whole code:

package brainydraw;
 
import java.awt.*;
import java.awt.event.*;
import java.awt.Graphics;
import javax.swing.*;
import javax.swing.JFrame;
 
 
public class OctagonDrag extends JFrame implements MouseMotionListener
{
    private int[] x = {150, 175, 175, 150, 100, 75, 75, 100};
    private int[] y = {150, 175, 175, 150, 100, 75, 75, 100};
    private Polygon p = new Polygon(x, y, 8);
    private int oldx; //Saves previous Polygon position
    private int oldy;
    private JFrame f = new JFrame();
 
    public void init()
    {
        setTitle("Poppy");
        setSize(300, 300);
        //setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        addMouseListener(new MousePressListener());
        addMouseMotionListener(this);
        MyPanel panel = new MyPanel();
        f.getContentPane().add(panel);
        setVisible(true);
        //panel.repaint();
    }
 
    class MyPanel extends JPanel
    {
        public void paintComponent(Graphics g)
        {
            g.setColor(Color.black);g.fillPolygon(p);
        }
 
   }
 
    public void mouseMoved(MouseEvent event)
    {
    }
 
    public void mouseDragged(MouseEvent event)
    {
        int x = event.getX();
        int y = event.getY();
        if (p.contains(x, y))
        {
            p.translate(x - oldx, y - oldy);
            oldx = x;
            oldy = y;
            repaint();
        }
    }
 
    class MousePressListener extends MouseAdapter
    {
 
        public void mousePressed(MouseEvent event)
        {
 
            int x = event.getX();
            int y = event.getY();
            if (p.contains(x, y))
            {
                oldx = x;
                oldy = y;
            }
        }
    }
 
    class CloseWindow implements WindowListener
    {
        public void windowClosing(WindowEvent event)
        {
            System.exit(0);
        }
        public void windowOpened(WindowEvent event)
        {
        }
        public void windowClosed(WindowEvent event)
        {
        }
        public void windowIconified(WindowEvent event)
        {
        }
        public void windowActivated(WindowEvent event)
        {
        }
        public void windowDeactivated(WindowEvent event)
        {
        }
        public void windowDeiconified(WindowEvent event)
        {
        }
    }
 
    public static void main(String[] args)
    {
        OctagonDrag test = new OctagonDrag();
        test.init();
 
    }
}

Thanks heaps

There are still a few things wrong with your code in general. First, no need to have your class extend JFrame when you are using a JFrame variable for most of everything (the init() function has confusion when setting values for OctagonDrag and the variable f, both of which are JFrames, one of which is not necessary in its present state). Second, you should always call super.paintComponent(g) in the paintComponent method. Next, the coordinates are not octagon coordinates, rather a line (change fillPolygon to drawPolygon and you will see what I mean). Next, re-read all the above posts because some of these considerations were noted already and I may have missed a few. Lastly, I'll reiterate Brt93yoda'sI'd recommendation to study the basic GUI tutorials over at sun even if you have already.

Thank you a lot copeg, your suggestion of "replace fillPolygon with drawPolygon" is so useful, I can see it is a line now. But how to change those coordinates to show a octagon?