分别For语岝、while语岝和do…while语岝用编写代码在主岟法中实岞岠罓1+1/2!+1/3!+…+1/20!

首先，我们来看一下如何使用for、while和do...while这三个循环结构来计算这个序列：

1. **For循环**:

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 20; i++) {
            double factorial = calculateFactorial(i);
            System.out.println(1 / factorial);
        }
    }

    private static double calculateFactorial(int n) {
        if (n == 0 || n == 1) return 1;
        else return n * calculateFactorial(n - 1);
    }
}

2. **While循环**:

public class Main {
    public static void main(String[] args) {
        int i = 1;
        while (i <= 20) {
            double factorial = calculateFactorial(i);
            System.out.println(1 / factorial);
            i++;
        }
    }

    private static double calculateFactorial(int n) {
        if (n == 0 || n == 1) return 1;
        else return n * calculateFactorial(n - 1);
    }
}

3. **Do...While循环**:

public class Main {
    public static void main(String[] args) {
        int i = 1;
        do {
            double factorial = calculateFactorial(i);
            System.out.println(1 / factorial);
            i++;
        } while (i <= 20);

        // 在do...while循环里，循环体至少会执行一次，所以在i++前添加对factorial的计算
    }

    private static double calculateFactorial(int n) {
        if (n == 0 || n == 1) return 1;
        else return n * calculateFactorial(n - 1);
    }
}

以上三种循环都会计算从1到20的阶乘倒数之和。