编写程序。分别用while语句、do-while语句和for语句编写一个求阶乘n!的java程序。

while语句：

import java.util.Scanner;

public class FactorialWhile {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int n = input.nextInt();
        int result = 1;
        int i = 1;
        while (i <= n) {
            result *= i;
            i++;
        }
        System.out.println(n + "! = " + result);
    }
}

do-while语句：

import java.util.Scanner;

public class FactorialDoWhile {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int n = input.nextInt();
        int result = 1;
        int i = 1;
        do {
            result *= i;
            i++;
        } while (i <= n);
        System.out.println(n + "! = " + result);
    }
}

for语句：

import java.util.Scanner;

public class FactorialFor {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入一个正整数：");
        int n = input.nextInt();
        int result = 1;
        for (int i = 1; i <= n; i++) {
            result *= i;
        }
        System.out.println(n + "! = " + result);
    }
}