java语言的科学与艺术-Rational(class)

/**
 * The Rational class is used to represent rational numbers, which
 * are defined to be the quotient of two integer.
 * @author Administrator
 *
 */
public class Rational {
    /** Creates a new Rational from the integer argument. */
    public Rational(){
        this(0);
    }
    
    /**
     * Creates a new Rational from the integer argument.
     * @param n The initial value
     */
    public Rational(int n){
        this(n,1);
    }
    
    /**
     * Creates a new Rational with the value x / y.
     * @param x The numerator of the rational number 
     * @param y The denominator of the rational number
     */
    public Rational(int x, int y) {
        int g = gcd(Math.abs(x), Math.abs(y));
        num = x / g;
        den = Math.abs(y) / g;
        if(y < 0) num = -num;
    } 
    
    /**
     * Adds the rational number r to this one and returns the sum.
     * @param r The rational number to be added
     * @return The sum of the current number and r
     */
    public Rational add(Rational r) {
        return new Rational(this.num * r.den + r.num * this.den, this.den * r.den);
    }
    
    /**
     * Subtracts the rational number r from this one.
     * @param r The rational number to be subtracted
     * @return The result of subtracting r from the current number
     */
    public Rational substract(Rational r) {
        return new Rational(this.num * r.den - r.num * this.den, this.den * r.den);
    }
    
    /**
     * Multiplies this number by the rational number r.
     * @param r The rational number used as a multiplier
     * @return The result of multiplying the current number by r
     */
    public Rational multiply(Rational r) {
        return new Rational(this.num * r.num, this.den * r.den);
    }
    
    /**
     * Divides this number by the rational number r.
     * @param r The rational number used as a divisor
     * @return The result of dividing the current number by r
     */

    public Rational divide(Rational r){
        return new Rational(this.num * r.den, this.den * r.num);
    }
    
    /**
     * Creates a string representation of this rational number.
     * @return The string representation of this rational number
     */
    public String toString() {
        if (den == 1) {
            return "" + num;
        } else {
            return num + "/" + den;
        }
    }
    
    /**
     * Calculates the greatest common divisor using Euclid's algorithm.
     * @param x First integer
     * @param y Second integer
     * @return The greatest common divisor of x and y
     */
    public int gcd (int x, int y) {
        int r = x % y;
        while (r != 0) {
            x = y;
            y = r;
            r = x % y;
        }
        return y;
    }
    /* Private instance variables */
    private int num; /* The numerator of this Rational  */
    private int den; /* The denominator of this Rational */
}