Сложение двух дробей(Обьекты)

/* Fraction.java */
  
import java.io.*;
 
/** The Fraction class implements non-negative fractions, i.e., rational 
 * numbers.   
 */
class Fraction {
  /** Constructs a Fraction n/d. 
   *  @param n is the numerator, assumed non-negative.
   *  @param d is the denominator, assumed positive.
   */
  Fraction(int n, int d) {
    numerator = n; 
    denominator = d;
  }
 
  /** Constructs a Fraction n/1. 
   *  @param n is the numerator, assumed non-negative.
   */
  public Fraction(int n) {
    this(n,1);
  }
 
  /** Constructs a Fraction 0/1. 
   */
  public Fraction() {
    numerator = 0;
    denominator = 1;
  }
 
  /** Converts this fraction to a string format: "numerator/denominator." 
   *  Fractions are printed in reduced form (part of your assignment is 
   *  to make this statement true).  
   *  @return a String representation of this Fraction.
   */
  public String toString()   {
    int thisGcd = gcd(numerator, denominator);
    
    return (numerator/thisGcd + "/" + denominator/thisGcd);
  }
 
  /** Calculates and returns the double floating point value of a fraction.
   *  @return a double floating point value for this Fraction.
   */
  public double evaluate()
    {
      double n = numerator; // convert to double
      double d = denominator;   
      return (n / d);       
    }
 
  /** Add f2 to this fraction and return the result. 
   * @param f2 is the fraction to be added.
   * @return the result of adding f2 to this Fraction.
   */
  public Fraction add (Fraction f2) {
    Fraction r = new Fraction((numerator * f2.denominator) + 
                  (f2.numerator * denominator),
                  (denominator * f2.denominator));    
    return r;
  }
 
  /** Computes the greatest common divisor (gcd) of the two inputs. 
   * @param x is assumed positive
   * @param y is assumed non-negative
   * @return the gcd of x and y
   */
  static private int gcd (int x, int y) {
    /* Remove the following line. */
    return 1;
  }
    
  /* private fields within a Fraction.           */ 
  private int numerator;
  private int denominator;
 
  /** Put the Fraction class through some test sequences.
   * @param argv is not used. 
   */
  public static void main(String[] argv) {
    
    /* Test all three contructors and toString. */
    Fraction f0 = new Fraction();
    Fraction f1 = new Fraction(3);
    Fraction f2 = new Fraction(12, 20);
 
    System.out.println("\nTesting constructors (and toString):");
    System.out.println("The fraction f0 is " + f0.toString()); 
    System.out.println("The fraction f1 is " + f1); // toString is implicit
    System.out.println("The fraction f2 is " + f2);
 
    /* Test methods on Fraction: add and evaluate. */
    System.out.println("\nTesting add and evaluate:");
    System.out.println("The floating point value of " + f1 + " is " + 
               f1.evaluate());
    System.out.println("The floating point value of " + f2 + " is " +
               f2.evaluate());
 
    /* 
    Fraction sumOfTwo = _______________;
    Fraction sumOfThree = ______________;
 
    System.out.println("The sum of " + f1 + " and " + f2 + " is " + sumOfTwo);
    System.out.println("The sum of " + f0 + ", " + f1 + " and " + f2 + " is "
               + sumOfThree);
    */
 
    /* Test gcd function (static method). */
    System.out.println("\nTesting gcd:");
    System.out.println("The gcd of 2 and 10 is: " + gcd(2, 10));
    System.out.println("The gcd of 15 and 5 is: " + gcd(15, 5));
    System.out.println("The gcd of 24 and 18 is: " + gcd(24, 18));
    System.out.println("The gcd of 10 and 10 is: " + gcd(10, 10));
    System.out.println("The gcd of 21 and 400 is: " + gcd(21, 400));
  }
}

public class Fraction {
    
    private double frac;
    
    Fraction (double frac){
        this.frac = frac;
    }
    
    public double get(){
        return frac;
    }
    
    public Fraction add(Fraction frac){
        return new Fraction(this.frac + frac.get());
    }
    
    public String toString(){
        return Double.toString(get());
    }
 
}

public class Main {
 
    public static void main(String... args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Введите дробное число d: ");
        double d = sc.nextDouble();
        Fraction frac1 = new Fraction(d);
        System.out.println("d = " + frac1.get());
        System.out.print("Введите дробное число f: ");
        double f = sc.nextDouble();
        Fraction frac2 = new Fraction(f);
        System.out.println("f = " + frac2.get());
        
        Fraction addFrac = frac1.add(frac2);
        System.out.printf("%-8.2f\n", addFrac.get());
 
        Fraction string = frac1;
        System.out.println(string.toString());
    }
 
}