java分别用while循环和for循环计算1+1/2!+1/3!+1/4!+……的前20项和

使用while循环计算1+1/2!+1/3!+1/4!+……的前20项和的Java代码如下：

public class Main {
    public static void main(String[] args) {
        int n = 1;
        double sum = 0, factorial = 1;
        while (n <= 20) {
            factorial *= n;
            sum += 1 / factorial;
            n++;
        }
        System.out.println("前20项和为：" + sum);
    }
}

使用for循环计算1+1/2!+1/3!+1/4!+……的前20项和的Java代码如下：

public class Main {
    public static void main(String[] args) {
        double sum = 0, factorial = 1;
        for (int n = 1; n <= 20; n++) {
            factorial *= n;
            sum += 1 / factorial;
        }
        System.out.println("前20项和为：" + sum);
    }
}

这两段代码的输出结果都为：前20项和为：1.7182818284590455