Passing values to seperate methods

Question

How do you pass integer values to different methods called in a program. Example: methods sum() and difference(). User has to enter two numbers. The program must print the numbers, calculate the sum and the difference, and then print the answers. I created a method that figured both the sum and difference with the use of the if / else procedure. I tried to create two seperate methods but could not get the second method to read and calculate the two numbers input. Below is what I ended up with.
import java.util.*;
Author:     Galen Rogers
Date:          09 July 06
Subject:     COM 209 Wk 3 Homework problem # 2.
Program to create "Sum & Difference" method.
public class NumbersCalc
     public static void sum()
          Scanner keyboard = new Scanner(System.in);
          int n1, n2, sum, diff;
          n1 = keyboard.nextInt();
          n2 = keyboard.nextInt();
          sum = n1 + n2;
          System.out.println("The sum of your numbers is: " + sum);
          if (n1 > n2)
               diff = n1 - n2;
          else
               diff = n2 - n1;
          System.out.println("The difference of your numbers is: " + diff);     
Main Program:
import java.util.*;
Author:     Galen Rogers
Date:          09 July 06
Subject:     COM 209 Wk 3 Homework problem # 2.
Program to add and subtract numbers entered by user and display answers.
public class Numbers
     public static void main(String[] args)
          Scanner keyboard = new Scanner(System.in);
          System.out.println("Please think of two whole numbers that you want calculated.");
          System.out.println("Please enter two whole numbers and press Enter after each number.");
          NumbersCalc.sum();
If any body can help I will really appreciate it.

Answer 1

Don't do input (or even output) inside the sum() or difference() methods. Instead get the input first, store the input into two variables and then call the two methods using the stored input. Make sure those methods return the calculated values and then print those values.
Your sum() method should look something like this:public int sum(int a, int b) {
  // just calculate result and return it
}Same for the difference() method.