使用while循环语句计算1+1/2！+1/3！+···+1/20！之和

public class Factorial {
/*  public static void main(String[] args){
double i;
i=SumFactorial(20);
System.out.println("1+1/2！+1/3！+···+1/20！之和: "+i);
}
public static double SumFactorial(int s){
int i=1;
double sum=0,den=1.0;  //sum是总和，den是分母
while(i<=s){
den=den*i;
sum+=1/den;
i++;
}
return  sum;
}*/
public static void main(String args[])
{
double sum = 0,a = 1;
int i = 1;
while(i <= 20)
{
sum = sum+a;
i = i+1;
a = a*(1.0/i);
}
System.out.println(sum);
}
}