java swing: previous paintings disappear

kpachopoulos · 03-11-2006, 11:39 AM

Hi,
an oval is created in graphArea (a JPanel) on mouseClicked. However, as soon as the mouse is clicked for the second (n-th) time, the first (previous) oval disappears and another oval appears on the new location. How can i keep the old the new ovals, too?
In general, how can i keep the old painted components and the new ones? (It has probably something to do with the repaint(), but i don't know what...)
A hint?

Code:

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

public class MainPanel extends JFrame
{     
    /*  To make a local variable available to an  
     *  inner class, just save a copy of the variable as a 
     *  final local variable.
     */
    
    int clickedX;
    int clickedY;
    JPanel graphArea;   
    JPanel outPanel;
    JPanel inPanel;
    
    public MainPanel() 
    {
        //setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(new Dimension(800, 600));        
        setLayout(new BorderLayout());
        
        /*  setting up the area of the graph    */
        graphArea=new JPanel()
        {
            public void paintComponent(Graphics g)
            {
                g.drawOval(clickedX,clickedY, 25,25);
                g.drawString("a",clickedX+13, clickedY+13);
            }
        };  
        
        graphArea.addMouseListener(new MouseAdapter()
        {
           public void mouseClicked (MouseEvent e)
           {
                clickedY=e.getY();
                clickedX=e.getX();
                System.out.println("Mouse clicked X: "+clickedX+" Y:"+clickedY);           
                repaint();      
           }
        });
        graphArea.setBorder(BorderFactory.createTitledBorder("graphArea"));
        graphArea.setPreferredSize(new Dimension(640, 340));        
        getContentPane().add(graphArea, BorderLayout.WEST);
        
        /* setting up the area of the outcoming connections */
        outPanel=new JPanel();
        outPanel.setBackground(Color.LIGHT_GRAY);
        addCheckBox(outPanel);
        outPanel.setBorder(BorderFactory.createTitledBorder("Outcoming Connections"));
        outPanel.setPreferredSize(new Dimension(120, 200));        
        getContentPane().add(outPanel,BorderLayout.PAGE_END);
        
        
        /* setting up the area of the incoming connections */
        inPanel=new JPanel();
        inPanel.setBackground(Color.LIGHT_GRAY);
        addCheckBox(inPanel);
        inPanel.setBorder(BorderFactory.createTitledBorder("Incoming Connections"));
        inPanel.setPreferredSize(new Dimension(160, 240));        
        getContentPane().add(inPanel,BorderLayout.LINE_END);
        
        setVisible(true);
    }    
    
    /*  provided, that num is even  */
    void addCheckBox(JPanel pane)
    {
        int j=0;
        for (int i=0; i<4; i++)
        {
            pane.add(new JCheckBox(Integer.toString(++j)));            
            pane.add(new JCheckBox(Integer.toString(++j)));
        }
    }

    public static void main(String[] args)
    {
        new MainPanel();
    }
    
}

kpachopoulos · 03-11-2006, 12:31 PM

Here it is...
Method repaint() clears the background. However, method updateUI() of JPanel, must be implemented on method update() of JComponent, which doesn't clear the background.

Code:

  graphArea.addMouseListener(new MouseAdapter()
        {
           public void mouseClicked (MouseEvent e)
           {
                clickedY=e.getY();
                clickedX=e.getX();
                System.out.println("Mouse clicked X: "+clickedX+" Y:"+clickedY);           
                graphArea.updateUI();      
           }
        });

paulsm4 · 03-11-2006, 12:39 PM

The only sure way to add multiple items to be displayed - and then to make sure they're all displayed each and every time the panel is refreshed (expose event, minimize/maximize, resize, etc) is:

a) Make a list of your graphics entities (an array, one or another Java container - etc)
b) Iterate through that list in your "paint()" method

Mega Man X · 03-11-2006, 01:47 PM

I did not understand the whole question, but I wrote this and it will keep the previous Oval thing. Is this what you were looking for?

Code:

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

public class DrawOval extends JFrame {

    private static int x, y;

    private JPanel pane = new JPanel();

    public DrawOval() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
	setSize(800, 600);
		
		
	pane.addMouseListener(new MouseAdapter() {
	    public void mouseClicked(MouseEvent e) {
	        x = e.getX();
		y = e.getY();
		System.out.println(e.toString());
	    }
	});
		
	getContentPane().add(pane);
		
	setVisible(true);
		
    }
	
    public static void main(String[] args) {
	new DrawOval();
    }

    public void paint (Graphics g) {
        super.repaint();
	g.setColor(Color.BLACK);
	g.drawOval(x, y, 30, 30);

    }

}

kpachopoulos · 03-12-2006, 03:24 AM

Hi Mega Man X,
you understood right. The repaint() does indirectly exactly what updateUI() and update() does. From the API:

Quote:

If this component is a lightweight component, this method causes a call to this component's paint method as soon as possible. Otherwise, this method causes a call to this component's update method as soon as possible.