Problem With Sliders and Area of a circle-

Question

Hey everyone--
New to Java and trying to work on an application where an oval is being manipulated by a slider and i have to caluculate and display the semi major(basically the diameter) and semi minor axes and caluculate the area of the ellipse. The center of the ellipse. should be on the center of the panel. A JSlider should be provided to alter the length of the major axis of the array. Note: the major axis may be along the x-axis (horizontal) or y-axis (vertical). The slider should be set up to represent percentage of the major axis. When the slider is at 0%, the major axis length would be equal to zero. When the slider is at 100%, the major axis length should be equal to the length of the JPanel.
The major part I am having trouble with is how to get the oval to start at the center of the JFrame and how to get the circle to stop at the ends of the width of the JFrame and the ends of the Height of the JFrame.
I have two different classes here they are below: the ovalPanel just draws a circle on it self and then the slider demo is an extension of that and is being used to calculate the area and semi major etc...
import java.awt.*;
import javax.swing.*;
public class ovalPanel extends JPanel
{  int diameter = 10;
public void paintComponent(Graphics g)
super.paintComponent(g);
g.fillOval(246,237,diameter,diameter);
public void setDiameter(int newDiameter)
diameter = (newDiameter >= 0 ? newDiameter : 10);
repaint();
public Dimension getPreferredSize()
return new Dimension(500,500);
public Dimension getMinimumSize()
return getPreferredSize();
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class sliderDemo extends JFrame
{  private JSlider diameterSlider;
private ovalPanel myPanel;
private JPanel textPanel;
private JTextField textField1, textField2, textField3;
private JLabel label1, label2, label3;
public sliderDemo()
super("Slider & Ellipse Demo");
myPanel = new ovalPanel();
myPanel.setBackground(Color.YELLOW);
diameterSlider= new JSlider(SwingConstants.HORIZONTAL, 0, 400, 10);
diameterSlider.setMajorTickSpacing(10);
diameterSlider.setPaintTicks(true);
diameterSlider.addChangeListener(
new ChangeListener()
     public void stateChanged(ChangeEvent e)
     myPanel.setDiameter(diameterSlider.getValue());
textField1= new JTextField(5);
textField2= new JTextField(5);
textField3= new JTextField(5);
label1=new JLabel("semiMajor: ");
label2=new JLabel("semiMinor: ");
label3=new JLabel(" Area: ");
textPanel = new JPanel();
textPanel.add(label1);
textPanel.setLayout(new GridLayout (1,3));
textPanel.add(textField1);
textPanel.add(label2);
textPanel.add(textField2);
textPanel.add(label3);
textPanel.add(textField3);
Container container = getContentPane();
container.add(diameterSlider, BorderLayout.SOUTH);
container.add(myPanel, BorderLayout.CENTER);
container.add(textPanel, BorderLayout.NORTH);
setSize(500, 500);
setVisible(true);
public static void main(String args [])
sliderDemo application = new sliderDemo();
application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Anyone help out with this--would be greatly appreciated
rich_crush

Answer 1

Here is a better description of what is needed :
Write a GUI application that displays an ellipse (oval) of variable size and calculates and displays the semi-major and semi-minor axes and the area of the ellipse. The size of an ellipse is determined by two constants, conventionally denoted a and b. The constant a equals the length of the semi-major axis (i.e. half of the length of the major axis); the constant b equals the length of the semi-minor axis (i.e. half of the length of minor axis).
The area enclosed by an ellipse is , where � is Math.PI.
All drawings must be done on a subclass of JPanel, and the result of the calculations should be displayed in JLabels. The center of the ellipse. should be on the center of the panel. A JSlider should be provided to alter the length of the major axis of the array. Note: the major axis may be along the x-axis (horizontal) or y-axis (vertical). The slider should be set up to represent percentage of the major axis. When the slider is at 0%, the major axis length would be equal to zero. When the slider is at 100%, the major axis length should be equal to the length of the JPanel. The initial major axis length should be at 1/2 of the panel length.
As the ellipse. changes, the lengths of the semi-major axis, semi-minor axis, and the area should be updated and displayed.
The animation below illustrates the Ellipse Slider program in motion. As you see, the drawn shape will be a circle until it grows big enough to touch the long sides of the JPanel, after which, it will grow as an ellipse (oval) until it touches the narrow sides of the panel.
Please help--very confused :)
rich_crush