有理数类

public class Rational {

    private int numerator;
    private int denominator;

    public Rational(int aNumerator, int aDenominator){
        int r = gcd(aDenominator, aNumerator);
        numerator = aNumerator / r;
        denominator = aDenominator / r;
        sign();
    }

    private static int gcd(int a, int b){
        if(b == 0){
            return a;
        }
        else{
            return gcd(b, a % b);
        }
    }

    private void sign(){
        if(denominator < 0){
            numerator = -numerator;
            denominator = -denominator;
        }
    }

    public Rational plus(Rational b){
        int d = this.denominator * b.denominator;
        int n = this.numerator * b.denominator + b.numerator * this.denominator;
        return new Rational(n, d);
    }

    public Rational minus(Rational b){
        int d = this.denominator * b.denominator;
        int n = this.numerator * b.denominator - b.numerator * this.denominator;
        return new Rational(n, d);
    }

    public Rational times(Rational b){
        int d = this.denominator * b.denominator;
        int n = this.numerator * b.numerator;
        return new Rational(n, d);
    }

    public Rational divides(Rational b){
        return times(new Rational(b.denominator, b.numerator));
    }

    public boolean equals(Object b){
        if(this == b)return true;
        if(b == null)return false;
        if(this.getClass() != b.getClass())return false;

        Rational that = (Rational)b;
        if(this.numerator == that.numerator && this.denominator == that.denominator)return true;
        return false;
    }

    public String toString(){
        return this.numerator + "/" + this.denominator;
    }

    public static void main(String[] args) {
        Rational a = new Rational(8, 30);
        Rational b = new Rational(32, 40);
        System.out.println("a = " + a);
        System.out.println("b = " + b);
        System.out.println("a + b = " + a.plus(b));
        System.out.println("a - b = " + a.minus(b));
        System.out.println("b - a = " + b.minus(a));
        System.out.println("a * b = " + a.times(b));
        System.out.println("a / b = " + a.divides(b));
        System.out.println("b / a = " + b.divides(a));
        System.out.println("a == b? " + (a.equals(b) == true? "true":"false"));
    }
    
}