Passing values between classes in two separate files

[Vern Vernetta]

So I'm using two separate files for the first time and seem to be having trouble passing the values. The program should add, subtract, multiply, and divide fractions printing the inputted fractions and the result.

The two files are as follows:

  
import java.util.Scanner;
public class P4
{
   public static void main(String [] args)
   {
      int numer1, denom1, numer2, denom2;// …
      char op;
      P4Rational a; // Rational arithmetic operands
      P4Rational b;
      P4Rational r; // Rational reference result
      Scanner scan = new Scanner(System.in);
      System.out.print("Enter fraction (+ - * /) arithmetic ");
      System.out.print("(exit ^D) ");
      System.out.print("\"1 / 2 + 1 / 4\": ");
      
      do
      {
         numer1 = scan.nextInt();
         scan.next();
         denom1 = scan.nextInt();
         a = new P4Rational(numer1, denom1); // Instantiate with 2 arg ctor
         
         op = scan.next().charAt(0);
         
         numer2 = scan.nextInt();
         scan.next();
         denom2 = scan.nextInt();
         b = new P4Rational(numer2, denom2);// Read in 2nd fraction
         
         switch( op )
         {
            case '+':
               r = a.add(b);
               System.out.println(a + " + " + b + " = " + r.toDoubleString());
               break;
            case '-':
               r = a.sub(b);
               System.out.println(a + " - " + b + " = " + r.toDoubleString());
               break;
            case '*':
               r = a.mult(b);
               System.out.println(a + " * " + b + " = " + r.toDoubleString());
               break;
            case '/':
               r = a.div(b);
               System.out.println(a + " / " + b + " = " + r.toDoubleString());
               break;
         }
         System.out.print("Enter fraction (+ - * /) arithmetic ");
         System.out.print("(exit ^D) ");
         System.out.print("\"1 / 2 + 1 / 4\": ");
      }while( scan.hasNext() ); // More lines of input
   System.exit(0);
   }  

and file two:

   
public class P4Rational
{
   private int numerator, denominator; // Rational number
   private P4Rational right;
   public P4Rational()
   /* */
   {
      numerator = 0;
      denominator = 2;
   }
   public P4Rational(int n)
   /* */
   {
      n = numerator;
   }
   public P4Rational(int n, int d)
   /* */
   {
	  n = numerator;
      d = denominator;
	  reduce();
   }
   public P4Rational add( P4Rational right)
   /* */
   {
	  return( new P4Rational(numerator+right.numerator, denominator));//wrong
   }
   public P4Rational sub( P4Rational right)
   /* */
   {
	   return( new P4Rational(numerator-right.numerator, denominator));//wrong
   }
   public P4Rational div( P4Rational right)
   /* */
   {
	   return( new P4Rational(numerator*right.denominator, denominator*right.numerator));
   }
   public P4Rational mult(P4Rational right)
   /* */
   {
      return( new P4Rational(numerator*right.numerator, denominator*right.denominator) );
   }
   public void reduce()
   {
      int gcd = 0; // Greatest common divisor
      int smaller = Math.min(numerator, denominator);
      for( int i = 2; i <= smaller; i++ ) // Find greatest common divisor
      {
         if( numerator % i == 0 && denominator % i == 0 )
         gcd = i;
      }
      if( gcd != 0 ) // Reduce fraction by gcd
      {
         numerator /= gcd;
         denominator /= gcd;
      }
   }
   public String toString()
   /* */
   {
      String str = numerator + " / " + denominator;
      return str;
   }
   public String toDoubleString()
   {
      return(Double.toString((double)numerator/denominator));
   }
}

When I try to run the program, it prints 0 / 0 fractions leading to a NaN result. My guess is that the values read in the first file are not being passed to the second file, but I'm unsure how to correct it.

I'd really appreciate any insight into why this is happening.

[Nicola Garofalo]

Look at your constructor in P4Rational. You assigned the values of your membrer variables to your local variables. It's not what you wanted to do.
Change your constructor

   public P4Rational(int n, int d)
   /* */
   {
	  n = numerator;
      d = denominator;
	  reduce();
   }

in the following one:

   public P4Rational(int n, int d)
   /* */
   {
	  numerator = n;
         denominator = d;
	  reduce();
   }

You did that in the one parameter constructor too:

   public P4Rational(int n)
   /* */
   {
      n = numerator;
   }

You must change it in:

   public P4Rational(int n)
   /* */
   {
       numerator = n;
   }

[Campbell Ritchie]

And welcome to the Ranch