有理数就是可以表示为两个整数的比值的数字。一般情况下，我们用近似的小数表示。但有些时候，不允许出现误差，必须用两个整数来表示一个有理数。

这时，我们可以建立一个“有理数类”，下面的代码初步实现了这个目标。为了简明，它只提供了加法和乘法运算。class Rational {

private long ra;

private long rb;

private long gcd(long a, long b) {

if(b == 0) return a;

return gcd(b, a % b);

}

public Rational(long a, long b) {

ra = a;

rb = b;

long k = gcd(ra, rb);

if(k > 1) { //需要约分

ra /= k;

rb /= k;

}

}

// 加法

public Rational add(Rational x) {

return ________________________________________; //填空位置

}

// 乘法

public Rational mul(Rational x) {

return new Rational(ra*x.ra, rb*x.rb);

}

public String toString() {

if(rb == 1) return "" + ra;

return ra + "/" + rb;

}

}

使用该类的示例：Rational a = new Rational(1,3);

Rational b = new Rational(1,6);

Rational c = a.add(b);

System.out.println(a + "+" + b + "=" + c);class Rational {

private long ra;

private long rb;

private long gcd(long a, long b) {

if (b == 0)

return a;

return gcd(b, a % b);

}

public Rational(long a, long b) {

ra = a;

rb = b;

long k = gcd(ra, rb);

if (k > 1) { // 需要约分

ra /= k;

rb /= k;

}

}

// 加法

public Rational add(Rational x) {

return new Rational(ra * x.rb + x.ra * rb, rb * x.rb); // 填空位置

}

// 乘法

public Rational mul(Rational x) {

return new Rational(ra * x.ra, rb * x.rb);

}

public String toString() {

if (rb == 1)

return "" + ra;

return ra + "/" + rb;

}

}

public class Main {

public static void main(String[] args) {

Rational a = new Rational(1, 3);

Rational b = new Rational(1, 6);

Rational c = a.add(b);

System.out.println(a + "+" + b + "=" + c);

}

}