Same instances should have same reference

Question

At the moment I have a class Fraction that allows me to create Fractions in three different ways

• With one Integer, in this case the given Integer will be the numerator and the denominator will be set to 1
• With 2 Integers, the numerator and the denominator
• The Last method would be to parse a String that has to match the REGEX -?\d+/[1-9]\d*

The generated Fractions will be reduced as far as possible with the gcd.

public class Fraction extends Number {

        public static final String REGEX = "-?\d+/[1-9]\d*";


        public static int gcd(int a, int b) {
          return b == 0 ? a : gcd(b, a % b);

        }


        public static Fraction parseFraction(String s) {
           if (!s.matches(REGEX)) {
              throw new RuntimeException("Parsing error");
           }
           String[] splitted = s.split("/");
           return new Fraction(Integer.parseInt(splitted[0]),
                   Integer.parseInt(splitted[1]));
        }

        private int numerator;

        private int denominator;


        public Fraction(int numerator) {
           this(numerator, 1);
        }


        public Fraction(int numerator, int denominator) {
           if (denominator == 0) {
              throw new RuntimeException("denominator == 0 is not  possible");
        }


       int gcd = Fraction.gcd(numerator, denominator);

       if (denominator / gcd < 0) {
         gcd *= -1;
       }

       this.numerator = numerator / gcd;

       this.denominator = denominator / gcd;
       }
     }

What I want to implement now is that Instances of Fraction with same numerator and denominator have the same Reference e.g.

 *Fraction.parseFraction("1/2").equals(Fraction.parseFraction("2/4"))*

should return true.

I looked into some chapters about Generics and Bounds, but im unsure if that is even the right direction of what I need. Should the Fraction class be bounded to String and Integer?

Answer 1

What I want to implement now is that Instances of Fraction with same numerator and denominator have the same Reference e.g.

I think you mean with the same value here?

You're going to run into issues calculating that value with ints (and also calculating with floats or doubles) -- figuring out why those things are difficult, and how you can mitigate them, will teach you a lot.

Read up on what String.intern() does (from e.g., this is just the first Google result: https://dzone.com/articles/string-interning-what-why-and), and do the same thing, but for your Fraction class.