# how to use math.pi in java

I am having problems converting this formula `V = 4/3 π r^3`. I used `Math.PI` and `Math.pow`, but I get this error:

‘;’ expected

Also, the diameter variable doesn’t work. Is there an error there?

``````import java.util.Scanner;

import javax.swing.JOptionPane;

public class NumericTypes
{
public static void main (String [] args)
{
double volume;
double diameter;

diameter = JOptionPane.showInputDialog("enter the diameter of a sphere.");

volume = (4 / 3) Math.PI * Math.pow(radius, 3);

+ "and the volume of the sphere is ");
}
}
``````

You’re missing the multiplication operator. Also, you want to do `4/3` in floating point, not integer math.

``````volume = (4.0 / 3) * Math.PI * Math.pow(radius, 3);
^^      ^
``````

Here is usage of `Math.PI` to find circumference of circle and Area First we take Radius as a string in Message Box and convert it into integer

``````public class circle {

public static void main(String[] args) {
// TODO code application logic here

JOptionPane.showMessageDialog(null, "Area: " + area,"AREA",JOptionPane.INFORMATION_MESSAGE);
JOptionPane.showMessageDialog(null, "circumference: " + circum, "Circumfernce",JOptionPane.INFORMATION_MESSAGE);
}

}
``````

Replace

``````volume = (4 / 3) Math.PI * Math.pow(radius, 3);
``````

With:

``````volume = (4 * Math.PI * Math.pow(radius, 3)) / 3;
``````

Your diameter variable won’t work because you’re trying to store a String into a variable that will only accept a double. In order for it to work you will need to parse it

Ex:

``````diameter = Double.parseDouble(JOptionPane.showInputDialog("enter the diameter of a sphere.");
``````