Thread: CylinderApplet

Hi, why doesn't this work?

import java.awt.Container;
import javax.swing.JApplet;
import javax.swing.JOptionPane;
import javax.swing.JTextArea;
 
public class CylinderApplet extends JApplet {
 
    public void init() 
    {
 
       String radiusStr = null ;
       String heightStr = null;
 
        double volume = 0;
        double radius= Double.parseDouble(radiusStr);
        double height= Double.parseDouble(heightStr);
 
        JTextArea outputArea= new JTextArea();
 
        Container container =getContentPane();
 
        container.add(outputArea);
 
 
 
         for (int i = 1; i <= 5; i++ ){
 
        radiusStr = JOptionPane.showInputDialog("Enter in the radius here");
        heightStr  = JOptionPane.showInputDialog("Enter in the radius here");
 
        outputArea.setText("The Volume of the Cylinder is" +volume);
         }
 
    }
       public double myvolume (double radius, double height)
        {
 
        double volume;
 
         volume= Math.PI*radius*radius*height;
 
        return volume;
 
     } // end of method
} // end of volume class

Define "doesn't work." Are you getting errors, incorrect results? If so, post the specifics (error messages, sample outputs, desired outputs, etc.) and ask specific questions.

Originally Posted by GregBrannon

Define "doesn't work." Are you getting errors, incorrect results? If so, post the specifics (error messages, sample outputs, desired outputs, etc.) and ask specific questions.

I'm sorry about that. The variables radius and height does not work, here are the errors from the console:

java.lang.NullPointerException
	at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
	at java.lang.Double.parseDouble(Unknown Source)
	at CylinderApplet.init(CylinderApplet.java:23)
	at sun.applet.AppletPanel.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)

The variables radiusStr and heightStr are defined as null and then parsed to obtain radius and height. You have the steps out of order. Reorder them so that you're not parsing nulls.

Okay, I changed it a bit and got the applet to start but now it returns a value of 0.0 when I type in the digits for radius and height.

import java.awt.Container;
import javax.swing.JApplet;
import javax.swing.JOptionPane;
import javax.swing.JTextArea;
 
public class CylinderApplet extends JApplet {
 
	public void init() 
	{
		String radiusStr = JOptionPane.showInputDialog("Enter in the radius here");
		String heightStr  = JOptionPane.showInputDialog("Enter in the radius here");
 
		double volume = 0;
		double radius = Double.parseDouble(radiusStr);
		double height = Double.parseDouble(heightStr);
 
 
		JTextArea outputArea = new JTextArea();
 
		Container container = getContentPane();
 
		container.add(outputArea);
 
		for (int i = 1; i <= 5; i++ ){
 
 
			radiusStr = null;
			heightStr = null;
 
			outputArea.setText("The Volume of the Cylinder is" +volume);
		}
 
	}
	public double myvolume (double radius, double height)
	{
 
		double volume;
 
		volume= Math.PI*radius*radius*height;
 
		return volume;
 
	} // end of method
} // end of volume class

Where do you compute the volume using radius and height?

In the loop?

Let me ask it another way. Where do you call the method myVolume() that computes/returns the volume based on radius and height?