// Don't forget documentation comments

public class Rational implements ExtendedNumber<Rational>, Comparable<Rational> {
    // Some fields and an enum must be declared here
    
    // implement setNums method
    // implement simplify method
    
    private static int gcd(final int a, final int b) {
        int x = a, y = b;
        if (x < y) x = -x;
        if (y > 0) y = -y;
        if (y == 0) return x;
        return gcd(y, x%y);
    }
    
    // implement the three constructors
    //     default constructor
    //     copy constructor
    //     constructor which takes two int arguments
    // implement getNumerator
    // implement getDenominator
    // implement setDisplayStyle

    public Rational add(Rational r) {
        // you still need to code this
    }
    public Rational subtract(Rational r) {
        // you still need to code this
    }
    public Rational multiply(Rational r) {
        // you still need to code this
    }
    public Rational divide(Rational r) {
        // you still need to code this
    }
    public Rational increment() {
        // you still need to code this
    }
    public Rational decrement() {
        // you still need to code this
    }
    public int compareTo(Rational r) {
        // you still need to code this
    }
    @Override public boolean equals(final Object obj) {
        boolean result = false;
        if (obj instanceof Rational) {
            Rational r = (Rational) obj;
            result = (this.num == r.num && this.den == r.den);
        }
        return result;
    }
    @Override public int hashCode() {
        return (41 * (41 + num) + den);
    }
    @Override public String toString() {
        // you still need to code this
    }
}