Beginner JAVA arithmetics/Math

[ZKR]

Hello.
An app I had to make for calculating sphere`s volume and surface area.
The code didn`t give the correct result for volume until I cast converted it`s value by adding (double), but it is a double from the beginning(?!):

import java.util.Scanner;
import java.text.DecimalFormat;

public class Sphere
{
	public static void main (String[] args)
	{
	Scanner scan = new Scanner (System.in);
	double radius, volume, surfaceArea, val;
	
	System.out.print ("Please enter sphere radius : ");
	radius = scan.nextDouble();
	
	volume = (double) 4/3 * Math.PI * Math.pow (radius, 3);	// [u]Lack of (double) conversion gave the result of:
	// 4/3 = 1 because of automatic integer conversion? and not 1.333333333333333[/u]
	
	surfaceArea = 4 * Math.PI * Math.pow (radius, 2);
	val = 4/3;													[u]//example of result in a double value converted to integer[/u]
	
	DecimalFormat fmt = new DecimalFormat ("0.####");
	
	System.out.println ("Sphere volume : " + fmt.format(volume));
	System.out.println ("Sphere surface area : " + fmt.format(surfaceArea));
	System.out.println ("4/3 = : " + val);                                                    [u]//example of result in a double value converted to integer - Printed[/u]
	}
}
// result of val = 4/3;	 is 1, not 1.333333333333333 but it`s a double.

Can someone explain please.

 

[Ijack]

I think you have answered your own question in your comments. 4 / 3 = 1, as both are integers. (double) 4 is a double, so (double) 4 / 3 = 1.3333....

You would get the same result by using 4.0 / 3 or 4.0 / 3.0.

 

[ZKR]

Yes it gave the same result with 4.0 (and so 3 converted by promotion to 3.0 too).
I thought it`s the variable type that counts.

Thanks

 

[ZKR]

Best answer selected by ZKR.