Rational.java

import java.io.*;
class Rational
{
    /*
     * Object oriented concept is misused here. Rational class doesn't need a
     * isPrime() method. isPrime() should ideally come under the Integer class
     */
    boolean isPrime(int n) // Java has boolean datatype
    {
        if(n < 2) // Remember, Prime numbers starts from 2
            return false;
        for(int j = 2; j * j <= n; j++) // It is enough to check from j=2 to j=sqrt(n)
        {
            if(n % j == 0)
                return false;
        }
        return true;
    }
    
    /*
     * Throwing exceptions out to the JVM environment is not a good habit.
     */
    public static void main(String args[]) throws IOException
    {
        Rational o = new Rational(); // o is not a good identifier as it looks like 0
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        //DataInputStream in = new DataInputStream(System.in);
        String str, n1, n2;
        int a, b, i, r1, r2, q1, q2, gcf; // q1 and q2 need not be set to zero; Small 'l' is not a good identifier as it resembles '1'.
        System.out.print("Enter the rational number: ");
        str = br.readLine();
        for(i = 0; str.charAt(i) != '/'; i++); // A while loop with initialization and increment is better written as a for loop
        n1 = str.substring(0,i);
        n2 = str.substring(i+1);
        a = Integer.parseInt(n1);
        b = Integer.parseInt(n2);
        q1 = a;
        q2 = b;
        if(q1<q2)
            gcf = a;
        else
            gcf = b;
        do
        {
            r1 = a%gcf;
            r2 = b%gcf;
            q1 = a/gcf;
            q2 = b/gcf;
            if(r1 != 0 || r2 != 0)
                gcf--;
            else
                break;
        }while(gcf != 0);
        if(q2 == 1)
        {
            System.out.println("Output: "+q1);
        }
        else
        {
            System.out.println("Output: "+q1 + "/" + q2);
        }
    }
}