java 常用类BigDecimal

import java.math.BigDecimal;

/**
 * @author
 * @create 2021-09-19 10:27
 * BigDecimal 学习笔记
 * 位于java.math保重
 * 作用:精确计算浮点数
 */
public class BigDecimalDemo {
    public static void main(String[] args) {
        double a = 1.0;
        double b = 0.9;
        // 精度丢失 0.09999999999999998
        //原因是 double 和float 在java内存中存放的是近似值
        System.out.println(a-b);
        double result = (1.4 - 0.5) / 0.9;
        //0.9999999999999999
        System.out.println(result);
        /*-----------------------减法-----------------------------------*/
        //一定要传字符串 0.1,应为double 存放的近似值
        BigDecimal subtract = new BigDecimal("1.0").subtract(new BigDecimal("0.9"));
        //测试传double
        BigDecimal bigDecimal = new BigDecimal(a);
       // 0.09999999999999997779553950749686919152736663818359375
        BigDecimal subtract1 = bigDecimal.subtract(new BigDecimal(b));
        System.out.println(subtract);
        System.out.println(subtract1);
        /*-------------------------乘法-----------------------------------------*/
        BigDecimal multiply = new BigDecimal("4").multiply(new BigDecimal("5"));
        System.out.println("乘法:"+multiply);
        /*--------------------------除法-----------------------------------------------*/
        //除法注意保留小数,有可能除不尽会报错BigDecimal.ROUND_HALF_UP 四舍五入
        //3.33
        BigDecimal divide = new BigDecimal("10").divide(new BigDecimal("3"), 2, BigDecimal.ROUND_HALF_UP);
        //5.000
        BigDecimal divided = new BigDecimal("10").divide(new BigDecimal("2"), 3, BigDecimal.ROUND_HALF_UP);
       // 0.5
        BigDecimal dividedd = new BigDecimal("0.9").divide(new BigDecimal("2"), 1, BigDecimal.ROUND_HALF_UP);
        System.out.println(dividedd);


    }


}