for迴圈語句：

import java.util.Scanner;
public class FactorialTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		System.out.print("請輸入一個正整數:"); 
		Scanner ScNumber=new Scanner(System.in);   
		int num=ScNumber.nextInt();       
		System.out.println();   
		int p = num;       
		for(int i=1;i<num;i++)
		{        
			p=p*(num-i);     
		}       
		System.out.println(num+"!="+p);
	}

}
 

while語句：

import java.util.Scanner;


public class FactorialTest1 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.print("請輸入一個正整數:"); 
		Scanner ScNumber=new Scanner(System.in);   
		int num=ScNumber.nextInt();       
		System.out.println(); 
		int p=num;
		int i=1;
		while(i<num)
		{
			p=p*(num-i);
			i++;
		}
		System.out.println(num+"!="+p);
	}

}
 

do.......while語句：

import java.util.Scanner;


public class FactorialTest2 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.print("請輸入一個正整數:"); 
		Scanner ScNumber=new Scanner(System.in);   
		int num=ScNumber.nextInt();       
		System.out.println(); 
		int p=num;
		int i=1;
		do
		{
			p=p*(num-i);
			i++;
		}while(i<num);
		System.out.println(num+"!="+p);	
	}

}