Java code

import java.util.*;
public class Calculator {
    int rc;
    static int src;
    double result;
    String s;
    String token;
    String operator;
    String expr;
    String peektoken;
    int cursor = 0;


    public static void main(String[] args)
    {
     Calculator x = new Calculator();
     src = x.process();

     return;
    }




    int process()
    {
        Scanner sc = new Scanner(System.in);
        boolean keepgoing = true;
        while(keepgoing == true)
           {
            String s = sc.nextLine();
            s = s.trim();
                if (s== null)
               {
                keepgoing = false;
                continue;
                System.out.println("The input is" + s);
                result = evalexpr(s);
               }
           }

      return 0;
    }



    double evalterm()
    {
       double a = evalfactor();
       token = peektoken();

        if((token.equals("*")) || (token.equals("/")))
        {
             operator = token;
             cursor++;
             double b = evalfactor();
                if (operator == "*")
                {
                 a=a*b;

                }else{

                 a=a/b;
           }
        }
       return a;
    }

    double evalexpr()
    {
        double x = evalterm();
        token = peektoken();

        if((token.equals("+")) || (token.equals("-")))
        {
            operator = token;
            cursor++;
            double y = evalterm();
                if (operator == "+")
                z = x + y;
                else
                z = x - y;
        }
        return x;
    }


    double evalfactor()
    {
        token = peektoken();
        if(token.equals("("));
        {
            cursor++;
            double K = evalexpr();

        return K;

        }
        else
        {
        cursor++;
        double m = Double.parseDouble(token);
    }
        return m;
    }



    String peektoken()
    {
        String s = "";
        while(cursor<expr.length())
        {
            s = expr.substring(cursor,cursor+1);

            if(s.matches("[0-9]"))
        {
            return s;
        }
            if(s.equals(" "))
        {
            cursor++;
            continue;
        }
        if(s.matches("[+-*/]"))
        {
        return s;
        }
        System.out.println("Error");
        return s;
        }
    }
}