Thread: Extends JPanel painting problem

Hello, sorry if this is in the wrong Forum Section but this seemed like the best place!

My problem is that I am currently designing a GUI that can display a Binary Search Tree (BST) from user entered data, I have the code nearly all working apart from the painting aspect of it. So I can enter all the data and everything into the BST fine but when it comes to painting there is problems for example when I first run the program and enter a value I want to displayed when I hit the add button which is suppose to draw a circle with the entered value inside it the circle and number will flash up and then disappear, I don't understand this as when I print out the BST using methods the value is definitely there etc. And if I add it again it will stay up and not flash away, it only seems to happen on the first circle so any others I add after that stay first time. Another problem is that if I either resize or navigate away from the GUI the BST that is displayed will vanish, again it's still stored but the painted BST will disappear. I think it may be because I haven't implemented the paintComponent method right or some problem with the area I paint on.

Below is some of the code that is relevant, if any more code or information is needed on this project to give a fuller picture I can put more up. Any help or advice or links on this matter would be so much help and I'd be very grateful! Thanks so much in advance!

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
 
public class PaintArea extends JPanel
{
	public static void main(String args[])
	{
		Runnable r;
		r = new Runnable()
		{
			public void run()
			{
				new PaintArea().startGUI();
			}
		};
 
		SwingUtilities.invokeLater(r);
 
	}
 
	public static void startGUI()
	{
 
		...
 
		//Create the painting area
		paintarea = new PaintArea();
		paintarea.setPreferredSize(new Dimension(480, 400));
		scrollpane  = new JScrollPane(paintarea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
		frame.add(scrollpane, BorderLayout.CENTER);
 
		...
 
		// create the add button
		add = new JButton();
		add.setText("Add...");
 
		// add actionListener to the add button
		add.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{	
				try
				{
					int i = Integer.parseInt(textField.getText());
 
					binarySearchTree.insert(i);
 
					double x = binarySearchTree.getX(binarySearchTree.getNode(i)); \\ Location in
					double y = binarySearchTree.getY(binarySearchTree.getNode(i)); \\ BST
					String LorR = binarySearchTree.getLorR(binarySearchTree.getNode(i)); 
					\\ Determine if it's a right or left node
 
					addcircle(paintarea, textField.getText(), x, y, LorR);
 
					statusField.setText(textField.getText() + " : Added to Binary Search Tree" + "\t" + 
						"Items in search tree : " + binarySearchTree.count());
 
					textField.setText("");
 
					textField.requestFocusInWindow();
				}
				catch(NumberFormatException er)
				{
					statusField.setText("No valid number to add" + "\t\t" + 
						"Items in search tree : " + binarySearchTree.count());
 
					textField.setText("");
 
					textField.requestFocusInWindow();
				}
			}
		});
 
		// add the button to the bottom bar
		buttonbar.add(add);
 
		...
 
	} // end startGUI
 
	public static void addcircle(PaintArea p, String i, double x, double y, String LorR)
 	{
    	Graphics g = p.getGraphics();
 
    	int offsetx = p.getWidth()/2;
    	int valuex = (int) (p.getWidth()/4.5);
    	int offsety = 20;
    	int valuey = p.getHeight()/8;
    	int circle = 20;
 
    	double nodex = x;
    	double nodey = y;
 
    	int postionx = offsetx + (int) (nodex * valuex); \\ Used to declare X location of node
    	int postiony = (int) (nodey * valuey) + offsety; \\ Used to declare Y location of node
 
        g.setColor(new Color(127, 255, 0));
        g.fillOval(postionx, postiony, circle, circle);
        g.setColor(Color.black);
        g.drawOval(postionx, postiony, circle, circle);
 
        if(LorR == "Left") \\ Used to draw a line to the node
        {
        	double prex = x + 1/(Math.pow(2.0, y-1));
        	double prey = nodey - 1;
 
    		int prepostionx = offsetx + (int) (prex * valuex);
    		int prepostiony = (int) (prey * valuey) + offsety;
 
        	g.drawLine(postionx + 10, postiony, prepostionx + 10, prepostiony + 20);    		
        }
        else if (LorR == "Right")
        {
        	double prex = x - 1/(Math.pow(2.0, y-1));
        	double prey = nodey - 1;
 
    		int prepostionx = offsetx + (int) (prex * valuex);
    		int prepostiony = (int) (prey * valuey) + offsety;
 
        	g.drawLine(postionx + 10, postiony, prepostionx + 10, prepostiony + 20);    		
        }
 
    	// put in numbers
    	g.drawString(i, postionx + 3, postiony + 15);       
	}
 
	public void paintComponent(Graphics g) {
		super.paintComponent(g);
	}
} // end class

Never never use getGraphics on a Component in client code. Learn the correct way to perform custom painting here:
http://download.oracle.com/docs/cd/E...ing/index.html

Thank you! So what I should be doing is making PaintArea extends JPanel its own class and leaving the other class as the GUI class? That link was very helpful thanks!