i cant run this program pls help???

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);


}
}

Please see the link in my signature on asking smart questions, and please use CODE tags when posting code. What's your question?

why did you use static on String af and bf? and yet you didnt assign any value for them.
consider this sequence:
1. i declare a String without assigning any value to it.
2. i convert "empty value" string to double..~
how can one person convert no value into a value..~

Quote:

---

Originally Posted by SuperPig

convert "empty value" string to double

---

An empty String and null are not the same thing

Code:

---

String s1; // null
String s2 = ""; // empty String

System.out.println(s1.length()); // NullPointerException
System.out.println(s2.length()); // displays 0

Integer.parseInt(s1); // NullPointerException
Integer.parseInt(s2); // NumberFormatException

System.out.println(s2.equals(s1)); // displays false
System.out.println(s1.equals(s2)); // NullPointerException

---

@op: don't double post threads: http://www.java-forums.org/new-java/...xceptions.html

Quote:

---

Originally Posted by Junky

An empty String and null are not the same thing

Code:

---

String s1; // null
String s2 = ""; // empty String

System.out.println(s1.length()); // NullPointerException
System.out.println(s2.length()); // displays 0

Integer.parseInt(s1); // NullPointerException
Integer.parseInt(s2); // NumberFormatException

System.out.println(s2.equals(s1)); // displays false
System.out.println(s1.equals(s2)); // NullPointerException

---

---

sorry sorry..~ i have forgotten the term - null...:frusty:

Null means uninitialized and makes some variable "empty". You can't do much with null variables or else you will get exceptions.

Quote:

---

Originally Posted by sunde887

Null means uninitialized and makes some variable "empty".

---

The point I was trying to get across is that a variable is never empty. It always holds a value. If you do not assign a value to an instance variable then it gets a default value. For primitives it gets the corresponding default value: int, long, double, float etc get 0, char gets the null char '\0' boolean is false and for reference types (ie object variables) the default value is the null reference.

OK I just realised that local variables can be unitialised and can be thought of as empty. But you still can not use them as the compiler will complain.