java26：大小数，大整数

BigDecimal类  大小数

对小数做精确计算时，double不能描述的时候，就要使用这个类BigDecimal对小数做精确计算

package day26;

import java.math.BigDecimal;

public class Demo01 {
	public static void main(String[] args){
		BigDecimal d1 = new BigDecimal("0.9999999999999999999999999999999999999999999999999999999999999999999999");
		BigDecimal d2 = new BigDecimal("0.0000000000000000000000000000000000000000000000000000000000000000000001");
		d1 = new BigDecimal("0.9999999999999999999999999999999999999999999999999999999999999999999999");
		d2 = new BigDecimal("0.0000000000000000000000000000000000000000000000000000000000000000000001");
		BigDecimal d3 = d1.add(d2);//+
		System.out.println(d3);
		
		d1 = new BigDecimal("0.9999999999999999999999999999999999999999999999999999999999999999999999");
		d2 = new BigDecimal("0.0000000000000000000000000000000000000000000000000000000000000000000001");
		d3 = d1.subtract(d2);//-
		System.out.println(d3);
		
		d1 = new BigDecimal("0.9999999999999999999999999999999999999999999999999999999999999999999999");
		d2 = new BigDecimal("0.0000000000000000000000000000000000000000000000000000000000000000000001");
		d3 = d1.multiply(d2);//*
		System.out.println(d3);
		
		d1 = new BigDecimal("0.9999999999999999999999999999999999999999999999999999999999999999999999");
		d2 = new BigDecimal("0.0000000000000000000000000000000000000000000000000000000000000000000001");
		d3 = d1.divide(d2);//÷
		System.out.println(d3);
		d1 = new BigDecimal("10");
		d2 = new BigDecimal("3");
		//			10÷3	保留8位 	四舍五入
		d3 = d1.divide(d2,8,BigDecimal.ROUND_HALF_UP);//÷
		System.out.println(d3);
		


	}
}

BigInteger

保存更长的整数，取值范围受内存限制，在long 不能满足的时候使用BigInteger

package day26;

import java.math.BigInteger;

public class Demo02 {
	public static void main(String[] args){
		int sum = 1;
		for(int i = 1;i<=200;i++){
			sum *=i;
		}
		System.out.println(sum);
		
		//BigInteger bSum = new BigInteger(1);
		BigInteger bSum = BigInteger.valueOf(1);
		for(int i = 1; i<=999;i++){
			bSum =bSum.multiply(BigInteger.valueOf(i));
		}
		System.out.println(bSum);

	}
}

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