[SOLVED] help about drawing graphs

[jacline]

Design and implement a simple GUI application (or applet) that displays the graph of a quadratic function, Ax2 + Bx. Below the plot should be two sliders which allow the user to interactively set the values of A & B, the display being updated continuously in response to any changes the user makes to the sliders.
this is my assignment i wrote some code but the graph doesnt move when i moved sliders can you help me?
Here is my code

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.util.*;
 
public class PlotLuckPanel extends JPanel
{
 	protected JPanel controls, graph, general;
 	protected JSlider aSlider, bSlider;
 	protected JLabel aLabel, bLabel;
  	int a, b;
  	
 	public PlotLuckPanel()
 	{
 		setLayout(new FlowLayout());
 		
 		setPreferredSize( new Dimension( 500, 500));
 		
 		aSlider = new JSlider( JSlider.HORIZONTAL, -100, 100, 0); 
 		bSlider = new JSlider( JSlider.HORIZONTAL, -100, 100, 0); 
 		
 		aSlider.setMajorTickSpacing(25);
 		aSlider.setMinorTickSpacing(5);
 		aSlider.setPaintTicks(true);
 		aSlider.setPaintLabels(true);
 		aSlider.setAlignmentX( Component.LEFT_ALIGNMENT);
 		
 		bSlider.setMajorTickSpacing(25);
 		bSlider.setMinorTickSpacing(5);
 		bSlider.setPaintTicks(true);
 		bSlider.setPaintLabels(true);
 		bSlider.setAlignmentX( Component.LEFT_ALIGNMENT);
 		
 		PlotLuckListener listener = new PlotLuckListener();
 		aSlider.addChangeListener( listener);
 		bSlider.addChangeListener( listener);
 		
 		a = aSlider.getValue();
 		b = bSlider.getValue();
 		
 		aLabel = new JLabel( "A");
 		bLabel = new JLabel( "B");
 		aLabel.setAlignmentX( Component.LEFT_ALIGNMENT);
 		bLabel.setAlignmentX( Component.LEFT_ALIGNMENT);
 		
 		controls = new JPanel();
 		controls.setLayout( new BoxLayout( controls, BoxLayout.Y_AXIS));
 		controls.add( aLabel);
 		controls.add( aSlider);
 		controls.add( Box.createRigidArea( new Dimension(0,30)));
 		controls.add( bLabel);
 		controls.add( bSlider);
 		
 		add(controls);
 		
 		graph = new JPanel();
 		graph.setPreferredSize( new Dimension( 250, 250));
 		graph.add(new Draw());
 		
 		 				
 		general = new JPanel();
 		general.setLayout( new BorderLayout());
 		general.add( graph, BorderLayout.NORTH);
 		general.add( controls, BorderLayout.SOUTH);
 		
 		add(general);

 		
  	}
  	
 private class Draw extends JPanel
 {
 	private int x1, x2, y1, y2;
 	private int a, b;
 	
 	public Draw()
 	{
 		setPreferredSize( new Dimension (500, 300)) ;
 	}
 	
	public void paintComponent( Graphics g)
	{
		super.paintComponent( g);
		x1 = 0; x2 = 0; y1 = 0; y2 = 0;
			
		while( x1 < 1000)
		{
			x2 = x1 + 1;
			y1 = a * x1 * x1 + b * x1;
			y2 = a * x2 * x2 + b * x2;
			g.drawLine( 200 + x1, 200 - y1,200 + x2, 200 - y2 );
			g.drawLine( 200 - x1, 200 - y1,200 - x2, 200 - y2 );
			x1 = x2;	
		}
	 } 	

 } 	
  	private class PlotLuckListener implements ChangeListener
 	{ 	 
 		Draw graph = new Draw();
 		
 		public void stateChanged( ChangeEvent e)
 		{
 			aSlider.setVisible( true);
 			bSlider.setVisible( true);
 			
			a = aSlider.getValue();
			b = bSlider.getValue();
			
			aLabel.setText( "A: " + a);
			bLabel.setText( "B: " + b);
		
			repaint();
 			
 		}
 	}
 }

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class PlotLuck 
{
public static void main(String[] args) 
    {
        JFrame frame = new JFrame("Bandit");
        
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add( new PlotLuckPanel());
        frame.pack();
        frame.setVisible(true);
    }
}

[hardwired]

Suggestions:
1 — FlowLayout is not a good choice for your Draw component. Inspect the bounds (r) of Draw after it is rendered (code below). Better to use the center section of a BorderLayout.

        public void paintComponent( Graphics g)
        {
            super.paintComponent( g);
            Graphics2D g2 = (Graphics2D)g;
            Rectangle r = getBounds();
            System.out.printf("width = %d  height = %d " +
                              "bounds = [%d, %d, %d, %d]%n",
                               getWidth(), getHeight(),
                               r.x, r.y, r.width, r.height);
            g2.setPaint(Color.magenta);
            g2.draw(r);
            g2.setPaint(Color.black);
            x1 = 0; x2 = 0; y1 = 0; y2 = 0;

            while( x1 < 1000)
            {
                x2 = x1 + 1;
                y1 = a * x1 * x1 + b * x1;
                y2 = a * x2 * x2 + b * x2;
                if(x1 == 200) {
                    System.out.printf("x1 = %d  y1 = %d%n", x1, y1);
                    g2.setPaint(Color.red);
                    g2.fill(new Ellipse2D.Double(x1-1.5, y1-1.5, 4, 4));
                    g2.setPaint(Color.green.darker());
                    g2.fill(new Ellipse2D.Double(200 + x1, 200 - y1, 4, 4));
                    g2.setPaint(Color.blue);
                    g2.drawLine(200, 200, x1, y1);
                    g2.setPaint(Color.black);
                }
                g.drawLine( 200 + x1, 200 - y1,200 + x2, 200 - y2 );
                g.drawLine( 200 - x1, 200 - y1,200 - x2, 200 - y2 );
                x1 = x2;
            }
        }

2 — Mount the sliders in a panel and add it to the south/last section of the BorderLayout.
3 — Code above gives some ideas about how to explore/investigate what is going on in your graphic component.
4 — For dynamic graphics, viz, fluid resizing behavior, consider using the width and height of the component for drawing, eg (pseudo code),

        protected void paintComponent( Graphics g)
        {
            super.paintComponent( g);
            Graphics2D g2 = (Graphics2D)g;
            int w = getWidth();
            int h = getHeight();
            // center of this component:
            int cx = w/2;
            int cy = h/2;
            g2.fill(new Ellipse2D.Double(cx-1.5, cy-1.5, 4, 4));