"缺少方法体"错误

Question

import java.util.Scanner;

public class Rpn_calculator
{
    public static void main(String[] args)
    {
        Scanner keyboard = new Scanner(System.in);


        double ans = 0;
        double n = 0;
        double r = 0;
        String j;


        System.out.println();
        System.out.println();   
        System.out.print("Please enter a value for n  ");
        n = keyboard.nextDouble();  
        System.out.print("Please enter a value for r  ");
        r = keyboard.nextDouble();  
        System.out.println("Please choose one of these operands:+,-,*,nCr,/ to     continue, or q to quit ");
        j = keyboard.nextLine();    
        while (j != "q")
        {
            if(j == "+")
                ans = n + r;
            if(j == "-")
                ans = n - r;
            if(j == "*")
                ans = n * r;
            if(j == "/")
                ans = n / r;
            if(j == "nCr")
                ans = factorial(n + r -1) / (factorial(r)*factorial(n - 1));
            System.out.print(ans);

            System.out.print("Please enter a value for n  ");
            n = keyboard.nextDouble();  
            System.out.print("Please enter a value for r  ");
            r = keyboard.nextDouble();  
            System.out.print("Please choose one of these operands:+,-,*,nCr,/ to continue or q to quit ");
            j = keyboard.nextLine();    
        }   
    }
    public static double factorial(double x);
    {   
        double sum = 1;
        int i; 
        for (i = 0; i<= x; i++);
        sum = sum * i;

        return sum;
    }
} 

我正在尝试为这个任务创建一个RPN计算器,我相信我有我需要的功能,但我的因子函数有语法错误.它说"缺少方法体".

另外,我不明白为什么,当我编译它时,我的字符串输入请求被完全忽略 - 将程序锁定在while循环中.我希望我不会错过一些非常明显的东西.

Answer 1

有几个分号,不应该有:

public static double factorial(double x); // <-- This one
{   
    double sum = 1;
    int i; 
    for (i = 0; i<= x; i++); // <-- This one
    sum = sum * i;

    return sum;
}

在签名后立即放置分号时,您没有方法体,因此出现错误.该for循环不会是一个编译器错误,但是这将是一个空循环.

另外,我认为你需要用来String.equals比较Java中的字符串,而不是==运算符.