We have modified your code. The code accepts two numbers from the user and then ask for the calculation they want. According to that, it will perform operations i.e. addition and subtraction.

import java.util.*;

public class calculator{
    public static void main(String args[]){
        Scanner vin = new Scanner(System.in); 
        double firstnum,secondnum,sum=0,sub=0,mul;
        System.out.print("Enter first number: "); 
        firstnum = vin.nextDouble();
        System.out.print("Enter second number: ");
        secondnum = vin.nextDouble();
        System.out.print("Enter 1 for addition,2 for subtraction: "); 
        double store=vin.nextDouble();
        if(store==1){
            sum=firstnum+secondnum; 
            System.out.println("sum is " + sum);
            } 
        if(store==2){
            if(firstnum>secondnum){
            sub=firstnum-secondnum;
            }
            else if(secondnum>firstnum){
            sub=secondnum-firstnum;
            }
            System.out.println("sub is " + sub); 
        }
    }
}