Modify the RationalNumber class so that it implements the Comparable interface.

Question

Modify the RationalNumber class so that it implements the Comparable interface. To perform the comparison, compute an equivalent floating point value from the numerator and denominator for both RationalNumber objects, then compare them using a tolerance value of 0.0001. Write a main driver to test your modifications.

Hint:

go to the end of this code (p.315)

//--------------------------------------------------------------
// Returns this rational number as a string.
//-----------------------------------------------------------
   public String toString()
   {
      String result;

      if (numerator == 0)
         result = "0";
      else
         if (denominator == 1)
            result = numerator + "";
         else
            result = numerator + "/" + denominator;

      return result;
   }

At this point insert this commment:

//-----------------------------------------------------------------
// Compares this RationalNumber2 object to the parameter.
//-----------------------------------------------------------------

Now insert the code that does what the comment says.

Now you need to modify RationalTester2.java . Begin by testing the Comparable nature of RationalNumber2 objects, like this:

public static void main(String[] args)
{
RationalNumber2 r1 = new RationalNumber2(6, 8);
RationalNumber2 r2 = new RationalNumber2(1, 3);

System.out.println("First rational number: " + r1);
System.out.println("Second rational number: " + r2);
int compareValue = r1.compareTo(r2);

if (compareValue == 0)
System.out.println("r1 and r2 are equal.");
else
if (compareValue < 0)
System.out.println("r1 is less than r2");
else
System.out.println("r1 is greater than r2");

RationalNumber2 r3 = new RationalNumber2(6, 7);
RationalNumber2 r4 = new RationalNumber2(6, 7);

You should be able to take it from here

Explanation / Answer

Below is your code: -

RelationalNumber.java

public class RationalNumber implements Comparable<RationalNumber> {
   private int numerator, denominator;

   public RationalNumber(int num, int den) {
       if (den == 0)
           den = 1;

       if (den < 0) {
           num = num * -1;
           den = den * -1;
       }
       numerator = num;
       denominator = den;
       reduce();
   }

   // To return numerator
   public int getNumerator() {
       return numerator;
   }

   // To return denominator
   public int getDenominator() {
       return denominator;
   }

   public RationalNumber reciprocal() {
       return new RationalNumber(denominator, numerator);
   } // End reciprocal

   // For adding rationals
   public RationalNumber add(RationalNumber op2) {
       int commonDenominator = denominator * op2.getDenominator();
       int num1 = numerator * op2.getDenominator();
       int num2 = op2.getNumerator() * denominator;
       int sum = num1 + num2;

       return new RationalNumber(sum, commonDenominator);
   } // End Addition

   // For subtracting rationals
   public RationalNumber subtract(RationalNumber op2) {
       int commonDenominator = denominator * op2.getDenominator();
       int num1 = numerator * op2.getDenominator();
       int num2 = op2.getNumerator() * denominator;
       int diff = num1 - num2;

       return new RationalNumber(diff, commonDenominator);
   } // End Subtraction

   public RationalNumber multiply(RationalNumber op2) {
       int num = numerator * op2.getNumerator();
       int den = denominator * op2.getDenominator();

       return new RationalNumber(num, den);
   } // End Multiply

   // For Dividing rationals
   public RationalNumber divide(RationalNumber op2) {
       return multiply(op2.reciprocal());
   } // End Divide

   public String toString() {
       String result;

       if (numerator == 0)
           result = "0";
       else if (denominator == 1)
           result = numerator + "";
       else
           result = numerator + "/" + denominator;

       return result;
   } // End toString

   // Reduced form
   private void reduce() {
       if (numerator != 0) {
           int common = gcd(Math.abs(numerator), denominator);
           numerator = numerator / common;
           denominator = denominator / common;
       }
   } // End Reduce

   private int gcd(int num1, int num2) {
       while (num1 != num2)
           if (num1 > num2)
               num1 = num1 - num2;
           else
               num2 = num2 - num1;
       return num1;
   } // End GCD

   @Override
   public int compareTo(RationalNumber o) {
       double div1 = (double) this.numerator / (double) this.denominator;
       double div2 = (double) o.numerator / (double) o.denominator;
       if ((this.numerator == o.getNumerator() && this.denominator == o.getDenominator())
               || (Math.abs(div1 - div2) < 0.0001)) {
           return 0;
       } else if ((div1 - div2) < 0) {
           return -1;
       } else {
           return 1;
       }

   }
} // End RationalNumber

RelationalTester2.java

public class RationalTester2 {
   public static void main(String[] args) {
       RationalNumber r1 = new RationalNumber(6, 8);
       RationalNumber r2 = new RationalNumber(1, 3);
       System.out.println("First rational number: " + r1);
       System.out.println("Second rational number: " + r2);
       int compareValue = r1.compareTo(r2);
       if (compareValue == 0)
           System.out.println("r1 and r2 are equal.");
       else if (compareValue < 0)
           System.out.println("r1 is less than r2");
       else
           System.out.println("r1 is greater than r2");
       RationalNumber r3 = new RationalNumber(6, 7);
       RationalNumber r4 = new RationalNumber(6, 7);
       System.out.println("Third rational number: " + r3);
       System.out.println("Fourth rational number: " + r4);
       compareValue = r3.compareTo(r4);
       if (compareValue == 0)
           System.out.println("r3 and r4 are equal.");
       else if (compareValue < 0)
           System.out.println("r3 is less than r4");
       else
           System.out.println("r3 is greater than r4");
   }
}

Sample Run: -

First rational number: 3/4
Second rational number: 1/3
r1 is greater than r2
Third rational number: 6/7
Fourth rational number: 6/7
r3 and r4 are equal.

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