//The Rational class public class

public class Rational
{
   private int n;
   private int d;

    /**
     * The default constructor for objects of class Rational.  Creates the rational number 1.
     */
    public Rational()

    {
        n = 1;
        d = 1;
    }

    /**
     * The alternate constructor for objects of class Rational.  Creates a rational number equivalent to n/d.
     * @param n The numerator of the rational number.
     * @param d The denominator of the rational number.
     */
    public Rational(int n, int d)
    {

      if(d == 0){
      throw new ZeroDenominatorException
     }
       this.n = n;
      this.d = d;


    /**
     * Get the value of the Numerator
     *
     * @return     the value of the numerator
     */
    public int getNumerator()
    {
        return n;
    }

    /**
     * Get the value of the Denominator
     *
     * @return     the value of the denominator
     */
    public int getDenominator()
    {
        return d;
    }


    /**
     * Negate a rational number r
     *
     * @return a new rational number that is negation of this number -r
     */
    public Rational negate()
    {
        Rational r = new Rational (-this.n, this.d);

        return r;
    }


    /**
     * Invert a rational number r
     *
     * @return a new rational number that is 1/r.
     */
    public Rational invert()
    {
        int newN = this.d;
        int newD = this.n;
        return new Rational (newN, newD);

    }





    /**
     * Add two rational numbers
     *
     * @param other the second argument of the add
     * @return a new rational number that is the sum of this and the other rational
     */
    public Rational add(Rational other)
    {
        int newN = (this.n*other.d+this.d*other.n);
        int newD = (this.d*other.d);

        return new Rational (newN, newD);

    }

     /**
     * Subtract a rational number t from this one r
     *
     * @param other the second argument of subtract
     * @return a new rational number that is r-t
     */
    public Rational subtract(Rational other)
    {
        int newN = (this.n*other.d-this.d*other.n);
        int newD = (this.d*other.d);

        return new Rational (newN, newD);

    }

    /**
     * Multiply two rational numbers
     *
     * @param other the second argument of multiply
     * @return a new rational number that is the sum of this object and the other rational.
     */
    public Rational multiply(Rational other)
    {
        int newN = (this.n*other.n);
        int newD = (this.d*other.d);


        return new Rational (newN, newD);


    }


     /**
     * Divide this rational number r by another one t
     *
     * @param other the second argument of divide
     * @return a new rational number that is r/t
     */
    public Rational divide(Rational other)
    {
        int newN = (this.n*other.d);
        int newD = (this.d*other.n);


        return new Rational(newN, newD);

    }



 /**
     * Put the rational number in normal form where the numerator
     * and the denominator share no common factors.  Guarantee that only the numerator
     * is negative.
     *
     */
    private void normalize()
    {
        int absN = Math.abs(n);
        int absD= Math.abs(d);
        int signD = d/absD;

        int GCD = gcd(absN, absD);
        n = (n / GCD) * signD;
        d = (d / GCD) * signD;

    }

    /**
     * Recursively compute the greatest common divisor of two positive integers
     *
     * @param a the first argument of gcd
     * @param b the second argument of gcd
     * @return the gcd of the two arguments
     */
    private int gcd(int a, int b)
    {
        int result = 0;
        if(a<b)
            result = gcd(b,a);
        else if(b==0)
            result = a;
        else
        {
            int remainder = a % b;
            result = gcd(b, remainder);
        }
        return result;
    }
}

-------------------------------------------------------------------------------------------------------------------------------------
public class ZeroDenominatorException extends RuntimeException
{

	public ZeroDenominatorException(String reason)
	{
		super(reason);
	}
}




---------------------------------------------------------------------------------------------------------------------------------------

public class RationalTest
{
    public static void main (String args[])
    {
        testConstructor();
        testNegate();
        testInvert();
        testAddSubtract();
        testMultiplyDivide();
    }


    public static void testConstructor()
    {
        System.out.println("TESTING the constructor, getNumerator, getDenominator");

        System.out.println("Trying default constructor");
        Rational r0 = new Rational();

        if(r0.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 1");
        }

        if(r0.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }

        System.out.println("Constructing 2/5");
        try{
            Rational r1 = new Rational(2, 5);
            System.out.println("     Passes");

            if(r1.getNumerator() == 2)
            {
                System.out.println("     Passes");
            }
            else
            {
                System.out.println("**** Fails - numerator not 2");
            }


            if(r1.getDenominator() == 5)
            {
                System.out.println("     Passes");
            }
            else
            {
                System.out.println("**** Fails - denominator not 5");
            }
        }
        catch(ZeroDenominatorException e)
        {
            System.out.println("**** Fails - exception thrown");
        }


        System.out.println("Trying 2/0");
        try{
            Rational r1 = new Rational(2, 0);
            System.out.println("**** Fails - no exception thrown");
        }
        catch(ZeroDenominatorException e)
        {
            System.out.println("     Passes");
        }


        System.out.println("Trying 42/30");
        Rational r2 = new Rational(42, 30);

        if(r2.getNumerator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 7");
        }

        if(r2.getDenominator() == 5)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 5");
        }



        System.out.println("Trying 6/-3");
        Rational r3 = new Rational(6, -3);

        if(r3.getNumerator() == -2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not -2");
        }

        if(r3.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Trying -6/-3");
        Rational r4 = new Rational(-6, -3);

        if(r4.getNumerator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 2");
        }

        if(r4.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }

        System.out.println("Trying -6/3");
        Rational r5 = new Rational(-6, 3);

        if(r5.getNumerator() == -2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not -2");
        }

        if(r5.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }

        System.out.println("Trying 0/3");
        Rational r6 = new Rational(0, 3);

        if(r6.getNumerator() == 0)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 0");
        }

        if(r6.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }
    System.out.println("Constructor tests finished");

    }


    public static void testNegate()
    {
        System.out.println();
        System.out.println();
        System.out.println("TESTING the negate method");

        System.out.println("Negate 1/2");
        Rational r1 = new Rational(1, 2);
        Rational r2 = r1.negate();

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of negate argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of negate argument");
        }

        if(r2.getNumerator() == -1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not -1");
        }
        if(r2.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 2");
        }


        System.out.println("Negate -2/3");
        r1 = new Rational(-2, 3);
        r2 = r1.negate();

        if(r1.getNumerator() == -2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of negate argument");
        }

        if(r1.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of negate argument");
        }

        if(r2.getNumerator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 2");
        }

        if(r2.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 3");
        }
        System.out.println("Negate tests finished");
    }



    public static void testInvert()
    {
        System.out.println();
        System.out.println();
        System.out.println("TESTING the invert method");

        System.out.println("Invert 1/2");
        Rational r1 = new Rational(1, 2);
        Rational r2 = r1.invert();

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of negate argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of negate argument");
        }

        if(r2.getNumerator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 2");
        }

        if(r2.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Invert -2/3");
        r1 = new Rational(-2, 3);
        r2 = r1.invert();

        if(r1.getNumerator() == -2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of negate argument");
        }

        if(r1.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of negate argument");
        }

        if(r2.getNumerator() == -3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not -3");
        }

        if(r2.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 2");
        }

        System.out.println("Invert 0/5");
        r1 = new Rational(0, 5);
        try
        {
            r2 = r1.invert();
            System.out.println("**** Fails - did not throw zero denominator exception");
        }
        catch(ZeroDenominatorException e)
        {
            System.out.println("     Passes");
        }
        System.out.println("Invert tests finished");
    }

    public static void testAddSubtract()
    {
        System.out.println();
        System.out.println();
        System.out.println("TESTING the add and subtract methods");

        System.out.println("Adding 1/2 and 1/2");
        Rational r1 = new Rational(1, 2);
        Rational r2 = r1.add(r1);

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of add argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of add argument");
        }

        if(r2.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 1");
        }

        if(r2.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Adding 4/7 and 3/5");
        r1 = new Rational(4, 7);
        r2 = new Rational(3, 5);
        Rational r3 = r1.add(r2);

        if(r1.getNumerator() == 4)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of first add argument");
        }

        if(r1.getDenominator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of first add argument");
        }


        if(r2.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of second add argument");
        }

        if(r2.getDenominator() == 5)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of second add argument");
        }

        if(r3.getNumerator() == 41)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 41");
        }

        if(r3.getDenominator() == 35)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 35");
        }

        System.out.println("Adding 1/2 and 1/6");
        r1 = new Rational(1, 2);
        r2 = new Rational(1, 6);
        r3 = r1.add(r2);

        if(r3.getNumerator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 2");
        }

        if(r3.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 3");
        }



        System.out.println("Subtracting 1/2 and 1/2");
        r1 = new Rational(1, 2);
        r2 = r1.subtract(r1);

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of subtract argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of subtract argument");
        }

        if(r2.getNumerator() == 0)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 0");
        }

        if(r2.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Subtracting 4/7 and 3/5");
        r1 = new Rational(4, 7);
        r2 = new Rational(3, 5);
        r3 = r1.subtract(r2);

        if(r1.getNumerator() == 4)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of first subtract argument");
        }

        if(r1.getDenominator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of first subtract argument");
        }


        if(r2.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of second subtract argument");
        }

        if(r2.getDenominator() == 5)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of second subtract argument");
        }

        if(r3.getNumerator() == -1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not -1");
        }

        if(r3.getDenominator() == 35)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 35");
        }

        System.out.println("Subtracting 1/2 and 1/6");
        r1 = new Rational(1, 2);
        r2 = new Rational(1, 6);
        r3 = r1.subtract(r2);

        if(r3.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 1");
        }

        if(r3.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 3");
        }
        System.out.println("Add/Subtract tests finished");
    }


    public static void testMultiplyDivide()
    {
        System.out.println();
        System.out.println();
        System.out.println("TESTING the multiply and divide methods");

        System.out.println("Multiply 1/2 and 1/2");
        Rational r1 = new Rational(1, 2);
        Rational r2 = r1.multiply(r1);

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of add argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of add argument");
        }

        if(r2.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 1");
        }

        if(r2.getDenominator() == 4)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 4");
        }


        System.out.println("Multiply 5/7 and 3/5");
        r1 = new Rational(5, 7);
        r2 = new Rational(3, 5);
        Rational r3 = r1.multiply(r2);

        if(r1.getNumerator() == 5)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of first add argument");
        }

        if(r1.getDenominator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of first add argument");
        }


        if(r2.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of second add argument");
        }

        if(r2.getDenominator() == 5)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of second add argument");
        }

        if(r3.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 3");
        }

        if(r3.getDenominator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 7");
        }

        System.out.println("Multiply 1/2 and 0/1");
        r1 = new Rational(1, 2);
        r2 = new Rational(0, 1);
        r3 = r1.multiply(r2);

        if(r3.getNumerator() == 0)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 0");
        }

        if(r3.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }



        System.out.println("Dividing 1/2 by 1/2");
        r1 = new Rational(1, 2);
        r2 = r1.divide(r1);

        if(r1.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of subtract argument");
        }

        if(r1.getDenominator() == 2)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of subtract argument");
        }

        if(r2.getNumerator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 1");
        }

        if(r2.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Dividing 4/7 by 3/28");
        r1 = new Rational(4, 7);
        r2 = new Rational(3, 28);
        r3 = r1.divide(r2);

        if(r1.getNumerator() == 4)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of first subtract argument");
        }

        if(r1.getDenominator() == 7)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of first subtract argument");
        }


        if(r2.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed numerator of second subtract argument");
        }

        if(r2.getDenominator() == 28)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - changed denominator of second subtract argument");
        }

        if(r3.getNumerator() == 16)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 16");
        }

        if(r3.getDenominator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 3");
        }

        System.out.println("Dividing 1/2 by 1/6");
        r1 = new Rational(1, 2);
        r2 = new Rational(1, 6);
        r3 = r1.divide(r2);

        if(r3.getNumerator() == 3)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - numerator not 3");
        }

        if(r3.getDenominator() == 1)
        {
            System.out.println("     Passes");
        }
        else
        {
            System.out.println("**** Fails - denominator not 1");
        }


        System.out.println("Dividing 1/2 by 0/1");
        r1 = new Rational(1, 2);
        r2 = new Rational(0, 1);
        try
        {
            r3 = r1.divide(r2);
            System.out.println("**** Fails - did not throw zero denominator exception");
        }
        catch(ZeroDenominatorException e)
        {
            System.out.println("     Passes");
        }
        System.out.println("Multiply/Divide tests finished");
    }

}