null value exceptions

[vibaviattigala]

import java.util.Scanner;

public class main {

static String af;
static String bf;


public static void main(String args[]) {

final double R = 1.0967 * (10000000);





double lowest = Double.parseDouble(af);
double highest = Double.parseDouble(bf);
double answer;


answer = R * (1 / (lowest * lowest) - 1 / (highest * highest));

System.out.println(
"Insert the lowest Energy level");
Scanner obj = new Scanner(System.in);
af = obj.nextLine();
System.out.println("Now,Insert Highest Energy level");
bf = obj.nextLine();
System.out.println("Wave Length is " + answer);


}
}

it shows null value exceptions why????

[sunde887]

af and bf aren't initialized and you tried parsing them. Also, you should use informative variable names, something short(one or two words), which explains what the variable represents.