用java求1+2！+3！+…+20！

以下是两种Java求1+2!+3!+...+20!的例子：

1.使用for循环和嵌套循环计算阶乘和

public class Test{
    public static void main(String[] args){
        System.out.println("1!2!+3!+……+20!=" + getSum(20));
    }
    public static long getSum(int n){
        int i, k, fac, sum = 0;
        for(i = 1; i <= n; i++){
            fac = 1;
            for(k = 1; k <= i; k++){
                fac = fac * k;
            }
            sum = sum + fac;
        }
        return sum;
    }
}

2.使用递归函数计算阶乘和

public class Prog21{
    public static void main(String[] args){
        long sum = 0;
        for(int i = 0; i < 20; i++){
            sum += factorial(i + 1);
        }
        System.out.println(sum);
    }
    //阶乘
    private static long factorial(int n){
        if(n == 1){
            return 1;        }
        return n * factorial(n - 1);
    }
}