3.9大数值

基本的整数和浮点数精度不过，可以使用java.math包中的BigInteger和BigDecimal

• BigInteger add(BigInteger other
• BigInteger subtract(BigInteger other)
• BigInteger multiply(BigInteger other)
• BigInteger divide(BigInteger other)
• BigInteger mod(BigInteger other)
  返回这个大整数和另一个大整数的和差积商余
• int compareTo(BigInteger other)
  这个大整数和另一个大整数相等返回0；大于返回正数；小于返回负数
  *static BigInteger valueOf(long x)
  返回值等于x
• 四舍五入方法：java.Math.roundingMode.HALF_UP

import java.math.*;
import java.util.*;
public class BigIntegerTest
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);

      System.out.print("How many numbers do you need to draw? ");
      int k = in.nextInt();

      System.out.print("What is the highest number you can draw? ");
      int n = in.nextInt();

/*
*计算二项式系数n*（n-1）*（n-2）*…（n-k+1）/（1*2*3*…*k）
*/

      BigInteger lotteryOdds = BigInteger.valueOf(1);

      for (int i = 1; i <= k; i++)
         lotteryOdds = lotteryOdds.multiply(BigInteger.valueOf(n - i + 1)).divide(BigInteger.valueOf(i));
//大数值的加减乘除都用方法

      System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");
   }
}