package com.zf.s2; //创建一个包 import java.math.BigInteger; //导入类 import java.util.ArrayList; import java.util.List; public class TextFactorial { //操作计算阶乘的类 public static int simpleCircle( int num){ //简单的循环计算的阶乘 int sum= 1 ; if (num< 0 ){ //判断传入数是否为负数 throw new IllegalArgumentException( "必须为正整数!" ); //抛出不合理参数异常 } for ( int i= 1 ;i<=num;i++){ //循环num sum *= i; //每循环一次进行乘法运算 } return sum; //返回阶乘的值 } public static int recursion( int num){ //利用递归计算阶乘 int sum= 1 ; if (num < 0 ) throw new IllegalArgumentException( "必须为正整数!" ); //抛出不合理参数异常 if (num== 1 ){ return 1 ; //根据条件,跳出循环 } else { sum=num * recursion(num- 1 ); //运用递归计算 return sum; } } public static long addArray( int num){ //数组添加计算阶乘 long []arr= new long [ 21 ]; //创建数组 arr[ 0 ]= 1 ; int last= 0 ; if (num>=arr.length){ throw new IllegalArgumentException( "传入的值太大" ); //抛出传入的数太大异常 } if (num < 0 ) throw new IllegalArgumentException( "必须为正整数!" ); //抛出不合理参数异常 while (last<num){ //建立满足小于传入数的while循环 arr[last+ 1 ]=arr[last]*(last+ 1 ); //进行运算 last++; //last先进行运算，再将last的值加1 } return arr[num]; } public static synchronized BigInteger bigNumber( int num){ //利用BigInteger类计算阶乘 ArrayList list = new ArrayList(); //创建集合数组 list.add(BigInteger.valueOf( 1 )); //往数组里添加一个数值 for ( int i = list.size(); i <= num; i++) { BigInteger lastfact = (BigInteger) list.get(i - 1 ); //获得第一个元素 BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(i)); //获得下一个数组 list.add(nextfact); } return (BigInteger) list.get(num); //返回数组中的下标为num的值 } public static void main(String []args){ //java程序的主入口处 int num= 5 ; int num1= 23 ; System.out.println( "简单的循环计算" +num+ "的阶乘为" //调用simpleCircle +simpleCircle(num)); System.out.println( "利用递归计算" +num+ "的阶乘为" //调用recursion +recursion(num)); System.out.println( "数组添加计算" +num+ "的阶乘为" //调用addArray +addArray(num)); System.out.println( "利用BigInteger类计算" +num1+ "的阶乘为" //调用bigNumber +bigNumber(num1)); } }
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