Add a private method simplify() to your Fraction class that converts a fraction to its simplest form. For example, the fraction 20 / 60 should be stored in the class instance variables as 1 / 3 (i.e. numerator = 1, denominator = 3). N.B.you will need a method to determine the Greatest Common Divisor (GCD. both of these methods (simplify and gcd) must be private.

Add a private method simplify() to your Fraction class that converts a fraction to its simplest form. For example, the fraction 20 / 60 should be stored in the class instance variables as 1 / 3 (i.e. numerator = 1, denominator = 3). N.B.you will need a method to determine the Greatest Common Divisor (GCD.
both of these methods (simplify and gcd) must be private. As
these methods are private, client programs cannot access them. They can only be accessed within the Fraction class. Given their purpose, it would mean that any Fraction class method that modifies the
instance variables (e.g.: input, add, constructor, set) should call the simplify() method to reduce the instance variables to their minimum values.

import java.util.ArrayList;
import java.util.Scanner;

class Fraction
{
private int n, d;
public Fraction()
{

this.n = this.d = 0;
}
public Fraction(int n, int d)
{

this.n = n;
this.d = d;
}

public int getNum()
{

return n;
}

public int getDen()
{

return d;
}

public boolean isZero()
{
return(getNum() == 0 && getDen() != 0);
}
public boolean isequals(Object c)
{
Fraction f = (Fraction) c;
return(Integer.compare(n,f.n))==0 && (Integer.compare(d,f.d)==0);
}

public String getSimplifiedFraction()
{
//Decalre the string variable result to store the result
String result = "";
//if the numerator and denominator both are zero
if(getNum() == 0 && getDen() == 0)
//result is zero
result = "0";
//if the numerator is zero and denominator is non-zero
else if(isZero())
//result is zero
result = "0";
//if the numerator is non-zero and denominator is zero
else if(getNum() != 0 && getDen() == 0)
//result is Undefined
result = "Undefined";
//for a defined and non-zero fraction
else
{
//if the remainder is zero
if(getNum() % getDen() == 0)
result = (getNum() / getDen()) + "";
//if the numerator and denominator both are greater than zero
else if(getNum() < 0 && getDen() < 0)
result = (getNum() * -1) + "/" + (getDen() * -1);
//if any of them is zero
else if(getNum() < 0 || getDen() < 0)
{
//if the numerator is greater than zero
if(getNum() < 0)
result = "-" + (getNum() * -1) + "/" + getDen(); // appending a sign.
//if the denominator is zero
else
result = "-" + getNum() + "/" + (getDen() * -1); // appending a sign.
}
//both are non-zero
else
result = (getNum() + "/" + getDen());
}
//return the result
return result;
}
//Define the method display() that displays the resultant fraction
public void display()
{
//Call and display the fraction
System.out.println(getSimplifiedFraction());
}

public Fraction add(Fraction rhs) {
Fraction sum = new Fraction();
sum.d = d * rhs.d;
sum.n = n * rhs.d + d * rhs.n;
sum.simplify();
return sum;
}
private void simplify()
{
int a,b;
if(Math.abs(n) > Math.abs(d))
{
a = Math.abs(n);
b = Math.abs(d);
}
else
{
a = Math.abs(d);
b = Math.abs(n);
}
int r = a%b;
while(r != 0)
{
a = b;
b = r;
r = a%b;
}
//divide numerator and denominator by b
n /= b;
d /= b;
}

}
//Define the class TestFraction
class TestFraction
{

//Define the main method
public static void main(String[] args)
{
//Declare the variables to store the numerator and denominator
String res;
int num, den, num1, den1;
//Declare an ArrayList to store the results
ArrayList<Fraction> fractions = new ArrayList<>();
//Create the object for scanner class
Scanner sc = new Scanner(System.in);
//use the do-while loop to iterate test the conditions
do
{
//Prompts the user to enter the numerator
System.out.print("Enter the num: ");
//Store the Integer part only
num = Integer.parseInt(sc.nextLine().trim());
//If the numerator is less than zero
if(num < 0)
//Break from loop
break;
//Prompts the user to enter the denominator
System.out.print("Enter the den: ");
//store the integer part only
den = Integer.parseInt(sc.nextLine().trim());
//Create the object of Fraction class
Fraction fraction = new Fraction(num, den);
System.out.print("Enter the num to compare: ");
num1 = Integer.parseInt(sc.nextLine().trim());
if(num1 < 0)
break;
System.out.print("Enter the den to compare: ");
den1 = Integer.parseInt(sc.nextLine().trim());
Fraction fraction1 = new Fraction(num1, den1);
if(fraction1.isequals(fraction))
{
System.out.println("\nTrue-> Second fraction is equal to First Fraction");
}
else
System.out.println("\nFalse-> Second fraction is not equal to First Fraction"); // if isequal() returns zero.
//Add the resultant fractions into the ArrayList
fractions.add(fraction);
//Display the resultant fraction
res = fraction.getSimplifiedFraction();
System.out.println("Fraction added to list as: " + res + "\n"); //result is stored in ‘res’ variable
}while(res != "0");

//Display all fractions that are stored in the ArrayList
System.out.println("\nDISPLAYING ALL FRACTIONS:\n" + "-------------------------");
//Use the loop to display the values stored in the ArrayList
for(Fraction fr : fractions)
fr.display();
//to print the new line
System.out.println();
sc.close();

Fraction f = new Fraction(4, 8);
System.out.println("1st fraction: ");
f.display();

Fraction fc = new Fraction(8, 24);
System.out.println("2nd fraction: ");
fc.display();

Fraction res1 = f.add(fc);
System.out.println("Sum: ");
res1.display();
}
}