写一个java有理数rational类，分子为整型p，分母为整型q,构造方法Rational(int p,int q),定义其加减乘除及toString()方法

在Java中，我们可以创建一个名为`Rational`的有理数类，它包含两个整型成员变量`public int numerator`表示分子，`public int denominator`表示分母。下面是一个简单的实现：

public class Rational {
    private int numerator;
    private int denominator;

    // 构造函数，接收分子和分母作为参数
    public Rational(int p, int q) {
        if (q != 0) {
            this.numerator = p;
            this.denominator = q;
        } else {
            throw new IllegalArgumentException("Denominator cannot be zero");
        }
    }

    // 加法方法
    public Rational add(Rational other) {
        int newNum = numerator * other.denominator + other.numerator * denominator;
        int newDen = denominator * other.denominator;
        return new Rational(newNum, newDen);
    }

    // 减法方法
    public Rational subtract(Rational other) {
        int newNum = numerator * other.denominator - other.numerator * denominator;
        return new Rational(newNum, denominator * other.denominator);
    }

    // 乘法方法
    public Rational multiply(Rational other) {
        return new Rational(numerator * other.numerator, denominator * other.denominator);
    }

    // 除法方法，需要检查除数是否为零
    public Rational divide(Rational other) {
        if (other.denominator != 0) {
            return new Rational(numerator * other.denominator, denominator * other.numerator);
        } else {
            throw new ArithmeticException("Cannot divide by zero");
        }
    }

    // toString()方法，用于将有理数转换为字符串展示
    @Override
    public String toString() {
        if (denominator > 0) {
            return numerator + "/" + denominator;
        } else {
            return numerator + " / (-" + (-denominator) + ")";
        }
    }
}

在这个类中，我们提供了基本的数学运算方法以及`toString()`方法，以方便打印有理数。注意，这里假设了除数不为零，实际应用中可能需要添加异常处理来处理这种边界情况。