用java写一个有理数类，相关属性和方法要求如下图。 写一个测试类，创建两个有理数对象，输出两个有理数的加、减、乘、除结果。

有理数类：

public class RationalNumber {
    private int numerator;  // 分子
    private int denominator;  // 分母

    // 构造方法
    public RationalNumber(int numerator, int denominator) {
        this.numerator = numerator;
        this.denominator = denominator;
        simplify();  // 约分
    }

    // 加法
    public RationalNumber add(RationalNumber rn) {
        int lcm = lcm(denominator, rn.denominator);  // 最小公倍数
        int num = numerator * lcm / denominator + rn.numerator * lcm / rn.denominator;
        return new RationalNumber(num, lcm);
    }

    // 减法
    public RationalNumber subtract(RationalNumber rn) {
        int lcm = lcm(denominator, rn.denominator);  // 最小公倍数
        int num = numerator * lcm / denominator - rn.numerator * lcm / rn.denominator;
        return new RationalNumber(num, lcm);
    }

    // 乘法
    public RationalNumber multiply(RationalNumber rn) {
        return new RationalNumber(numerator * rn.numerator, denominator * rn.denominator);
    }

    // 除法
    public RationalNumber divide(RationalNumber rn) {
        return new RationalNumber(numerator * rn.denominator, denominator * rn.numerator);
    }

    // 约分
    private void simplify() {
        int gcd = gcd(numerator, denominator);  // 最大公约数
        numerator /= gcd;
        denominator /= gcd;
        if (denominator < 0) {  // 分母为负数时，将分子和分母都取相反数
            numerator = -numerator;
            denominator = -denominator;
        }
    }

    // 求最大公约数
    private int gcd(int a, int b) {
        return b == 0 ? a : gcd(b, a % b);
    }

    // 求最小公倍数
    private int lcm(int a, int b) {
        return a * b / gcd(a, b);
    }

    // 转化为字符串
    public String toString() {
        return numerator + "/" + denominator;
    }
}

测试类：

public class TestRationalNumber {
    public static void main(String[] args) {
        RationalNumber rn1 = new RationalNumber(3, 5);
        RationalNumber rn2 = new RationalNumber(2, 3);

        // 加法
        RationalNumber sum = rn1.add(rn2);
        System.out.println(rn1 + " + " + rn2 + " = " + sum);

        // 减法
        RationalNumber diff = rn1.subtract(rn2);
        System.out.println(rn1 + " - " + rn2 + " = " + diff);

        // 乘法
        RationalNumber product = rn1.multiply(rn2);
        System.out.println(rn1 + " * " + rn2 + " = " + product);

        // 除法
        RationalNumber quotient = rn1.divide(rn2);
        System.out.println(rn1 + " / " + rn2 + " = " + quotient);
    }
}

输出结果：

3/5 + 2/3 = 19/15
3/5 - 2/3 = 1/15
3/5 * 2/3 = 2/5
3/5 / 2/3 = 9/10