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。 我在使用main方法和main方法之后的行时遇到问题，为什么main方法之后的行显示非法的表达式开始？ 是因为我忘了在某处放括号还是我的代码错误？？ 该代码假设用分数执行算术运算。

公共类有理{

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。您可以创建一个文件 Sum.java其中包含 Sum 类。喜欢这个：

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;
    }
}

现在你可以创建一个名为 Main 的文件.java 你的 Main 类将成为你的程序的入口点，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都放在你的主方法里。