java写一个方法，输入任意一个整数，返回它的阶乘！用递归吧！！

这个方法最高效
import java.util.Scanner;

public class CalcFacSum {

public static void main(String[] args) {

System.out.print("Please input the number to calcualte factor sum: ");
int input = new Scanner(System.in).nextInt();

long sum = calcFacSum(input);
System.out.println("1! + 2! + .." + input + "! = " + sum);
}

public static long calcFacSum(int num) {
long fac = 1L;
long sum = 0L;
for (int i = 1; i <= num; i++) {
fac = fac * i;
sum += fac;
}

return sum;
}

}

---------------测试
Please input the number to calcualte factor sum: 5
1! + 2! + ..5! = 153本回答被提问者采纳

import java.util.Scanner;
public class factorial{
public static int factorial2(int x) {
if (x <= 1) {
return 1;
} else
return x * factorial(x - 1);
}
public static void main(String args[]) {
Scanner in = new Scanner(System.in);
System.out.println("请输入任意一个整数:");
int a = in.nextInt();
System.out.print(factorial(a));
}
}

java里有自己带的方法……Math.pow(）