Question

Write a Comparator to compare two Rationals so that a/b>c/d if a>c i.e. sort by increasing order of numerators only. Test your program by modifying the code below. Note do NOT change the Rational class in order to solve this problem.

Code:

public class Rational implements Comparable<Rational>
{
   //Declaring instance variables
double numerator = 0;
double denominator = 1;
//Parameterized constructor
public Rational(double n,double d){
numerator=n;
denominator=d;
}
// getters and setters
public void setNumerator(double value) {
this.numerator = value;
}
public void setDenominator(double value) {
this.denominator = value;
}
public double getNumerator() {
return this.numerator;
}
public double getDenominator() {
return this.denominator;
}

  
// -----------------------------------------------------------------
// 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;
}
   @Override
   public int compareTo(Rational o) {
       int val = 0;
       double currVal = numerator/denominator;

       Rational r = (Rational) o;
       double paraVal = o.getNumerator()/o.getDenominator();

       if (currVal > paraVal)
       val = 1;
       else if (currVal < paraVal)
       val = -1;
       else if (currVal == paraVal)
       val = 0;
       return val;
   }

}
_____________________

// Test.java

import java.util.ArrayList;
import java.util.Collections;

public class Test {

   public static void main(String[] args) {
  
   ArrayList<Rational> arl=new ArrayList<Rational>();
   arl.add(new Rational(1, 3));
   arl.add(new Rational(2, 7));
   arl.add(new Rational(1, -4));
   arl.add(new Rational(3, 11));
   arl.add(new Rational(5, 8));
   arl.add(new Rational(1, 2));
  
   System.out.println("_____ Displaying the Rational numbers before Sorting _____");
   for(int i=0;i<arl.size();i++)
   {
       System.out.println(arl.get(i));
   }
   Collections.sort(arl);
   System.out.println("_____ Displaying the Rational numbers after Sorting _____");
   for(int i=0;i<arl.size();i++)
   {
       System.out.println(arl.get(i));
   }
  

   }

}

Answer 1

import java.util.Comparator;

public class NumeratorComparator implements Comparator<Rational> {
    @Override
    public int compare(Rational o1, Rational o2) {
        return Double.compare(o1.getNumerator(), o2.getNumerator());
    }
}

import java.util.ArrayList;
import java.util.Collections;

public class Test {

    public static void main(String[] args) {

        ArrayList<Rational> arl = new ArrayList<Rational>();
        arl.add(new Rational(1, 3));
        arl.add(new Rational(2, 7));
        arl.add(new Rational(1, -4));
        arl.add(new Rational(3, 11));
        arl.add(new Rational(5, 8));
        arl.add(new Rational(1, 2));

        System.out.println("_____ Displaying the Rational numbers before Sorting _____");
        for (int i = 0; i < arl.size(); i++) {
            System.out.println(arl.get(i));
        }
        Collections.sort(arl, new NumeratorComparator());
        System.out.println("_____ Displaying the Rational numbers after Sorting _____");
        for (int i = 0; i < arl.size(); i++) {
            System.out.println(arl.get(i));
        }


    }

}