请解释如何在我的代码中实现main方法？

Question

请解释如何实现main方法。我主要方法和主方法后的行有问题，为什么主方法后的行显示非法启动表达式？是因为我忘了把括号放在某处或我的代码错了？代码假设用分数执行算术。

公共类Rational {

public static void main(String [] args){
    public int numerator;
    public int denominator;

public Rational(int numerator, int denominator)

{
    this.numerator = numerator;
    this.denominator = denominator;
    reduce();
}

public Rational add(Rational other)
{
    int num = numerator * other.denominator + other.numerator * denominator;
    int den = denominator * other.denominator;
    return new Rational(num, den);
}

public Rational subtract(Rational other)
{
    int num = numerator * other.denominator - other.numerator * denominator;
    int den = denominator * other.denominator;
    return new Rational(num, den);
}

public Rational multiply(Rational other)
{
    int num = numerator * other.numerator;
    int den = denominator * other.denominator;
    return new Rational(num, den);
}

public Rational divide(Rational other)
{
    int num = numerator * other.denominator;
    int den = denominator * other.numerator;
    return new Rational(num, den);
}

private void reduce()
{
    int min = 0;
    if(numerator > denominator)
    {
        min = denominator;
    }
    else
    {
        min = numerator;
    }

    for(int i = min; i > 1; i--)
    {
        boolean isNumDiv = numerator % i == 0;
        boolean isDenDiv = denominator % i == 0;

        if(isNumDiv && isDenDiv)
        {
            numerator = numerator / i;
            denominator = denominator / i;
            break;
        }
    }
}

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

} }

Answer 1

假设您必须创建一个打印总和的程序。您可以使用其中的Sum类创建一个Sum.java文件。像这样：

public class Sum {
    public int x;
    public int y;

    public Sum(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int sumMyNumbers() {
        return x + y;
    }

}

现在，您可以使用Main类创建一个名为Main.java的文件，该类将是程序的入口点，它可以是这样的：

public class Main {
    public static void main(String[] args) {
        // It will print the number 4 on your console
        System.out.println(new Sum(2, 2).sumMyNumbers());

        // Or like this:
        Sum mySum = new Sum(2,2);
        System.out.println(mySum.sumMyNumbers());

        // Or even like this:
        int i = new Sum(2, 2).sumMyNumbers();
        System.out.println(i);
    }
}

所以你的第一个错误是你把所有东西放在主方法中。