java BigDecimal

package com.qjx.springbootmybatis.Test;

import java.math.BigDecimal;

/**
 * @ClassName:MTest
 * @Author:QinJinxiang
 * @Date:2018/6/27 17:56
 * @Description:TODO
 **/
public class MTest {
    public static void main(String[] args) {
        System.out.println("---------------");

        ROUND_UP();
        System.out.println("---------------");

        ROUND_DOWN();
        System.out.println("---------------");


        ROUND_CEILING();
        System.out.println("---------------");


        ROUND_FLOOR();
        System.out.println("---------------");


        ROUND_HALF_UP();
        System.out.println("---------------");


        ROUND_HALF_DOWN();
        System.out.println("---------------");


        ROUND_HALF_EVEN();
        System.out.println("---------------");


        ROUND_UNNECESSARY();
        System.out.println("---------------");


    }

    private static void ROUND_UP(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_UP);
        System.out.println("ROUND_UP -12.4444 = "+f);

    }

    private static void ROUND_DOWN(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_DOWN);
        System.out.println("ROUND_DOWN -12.4444 = "+f);
    }

    private static void ROUND_CEILING(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_CEILING);
        System.out.println("ROUND_CEILING -12.4444 = "+f);
    }

    private static void ROUND_FLOOR(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_FLOOR);
        System.out.println("ROUND_FLOOR -12.4444 = "+f);
    }

    private static void ROUND_HALF_UP(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_HALF_UP);
        System.out.println("ROUND_HALF_UP -12.4444 = "+f);
    }

    private static void ROUND_HALF_DOWN(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_HALF_DOWN);
        System.out.println("ROUND_HALF_DOWN -12.4444 = "+f);
    }

    private static void ROUND_HALF_EVEN(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_HALF_EVEN);
        System.out.println("ROUND_HALF_EVEN -12.4444 = "+f);
    }

    private static void ROUND_UNNECESSARY(){
        BigDecimal a =new BigDecimal(String.valueOf(12.5555)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY 12.5555 = "+a);

        BigDecimal b =new BigDecimal(String.valueOf(12.6666)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY 12.6666 = "+b);

        BigDecimal c =new BigDecimal(String.valueOf(12.4444)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY 12.4444 = "+c);

        BigDecimal d =new BigDecimal(String.valueOf(-12.5555)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY -12.5555 = "+d);

        BigDecimal e =new BigDecimal(String.valueOf(-12.6666)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY -12.6666 = "+e);

        BigDecimal f =new BigDecimal(String.valueOf(-12.4444)).setScale(2,BigDecimal.ROUND_UNNECESSARY);
        System.out.println("ROUND_UNNECESSARY -12.4444 = "+f);
    }
    
}

运行结果：
---------------
ROUND_UP 12.5555 = 12.56
ROUND_UP 12.6666 = 12.67
ROUND_UP 12.4444 = 12.45
ROUND_UP -12.5555 = -12.56
ROUND_UP -12.6666 = -12.67
ROUND_UP -12.4444 = -12.45
---------------
ROUND_DOWN 12.5555 = 12.55
ROUND_DOWN 12.6666 = 12.66
ROUND_DOWN 12.4444 = 12.44
ROUND_DOWN -12.5555 = -12.55
ROUND_DOWN -12.6666 = -12.66
ROUND_DOWN -12.4444 = -12.44
---------------
ROUND_CEILING 12.5555 = 12.56
ROUND_CEILING 12.6666 = 12.67
ROUND_CEILING 12.4444 = 12.45
ROUND_CEILING -12.5555 = -12.55
ROUND_CEILING -12.6666 = -12.66
ROUND_CEILING -12.4444 = -12.44
---------------
ROUND_FLOOR 12.5555 = 12.55
ROUND_FLOOR 12.6666 = 12.66
ROUND_FLOOR 12.4444 = 12.44
ROUND_FLOOR -12.5555 = -12.56
ROUND_FLOOR -12.6666 = -12.67
ROUND_FLOOR -12.4444 = -12.45
---------------
ROUND_HALF_UP 12.5555 = 12.56
ROUND_HALF_UP 12.6666 = 12.67
ROUND_HALF_UP 12.4444 = 12.44
ROUND_HALF_UP -12.5555 = -12.56
ROUND_HALF_UP -12.6666 = -12.67
ROUND_HALF_UP -12.4444 = -12.44
---------------
ROUND_HALF_DOWN 12.5555 = 12.56
ROUND_HALF_DOWN 12.6666 = 12.67
ROUND_HALF_DOWN 12.4444 = 12.44
ROUND_HALF_DOWN -12.5555 = -12.56
ROUND_HALF_DOWN -12.6666 = -12.67
ROUND_HALF_DOWN -12.4444 = -12.44
---------------
ROUND_HALF_EVEN 12.5555 = 12.56
ROUND_HALF_EVEN 12.6666 = 12.67
ROUND_HALF_EVEN 12.4444 = 12.44
ROUND_HALF_EVEN -12.5555 = -12.56
ROUND_HALF_EVEN -12.6666 = -12.67
ROUND_HALF_EVEN -12.4444 = -12.44
---------------

在银行、帐户、计费等领域，BigDecimal提供了精确的数值计算。其中8种舍入方式值得掌握。

1、ROUND_UP

舍入远离零的舍入模式。

在丢弃非零部分之前始终增加数字(始终对非零舍弃部分前面的数字加1)。

注意，此舍入模式始终不会减少计算值的大小。

2、ROUND_DOWN

接近零的舍入模式。

在丢弃某部分之前始终不增加数字(从不对舍弃部分前面的数字加1，即截短)。

注意，此舍入模式始终不会增加计算值的大小。

3、ROUND_CEILING

接近正无穷大的舍入模式。

如果 BigDecimal 为正，则舍入行为与 ROUND_UP 相同;

如果为负，则舍入行为与 ROUND_DOWN 相同。

注意，此舍入模式始终不会减少计算值。

4、ROUND_FLOOR

接近负无穷大的舍入模式。

如果 BigDecimal 为正，则舍入行为与 ROUND_DOWN 相同;

如果为负，则舍入行为与 ROUND_UP 相同。

注意，此舍入模式始终不会增加计算值。

5、ROUND_HALF_UP

向“最接近的”数字舍入，如果与两个相邻数字的距离相等，则为向上舍入的舍入模式。

如果舍弃部分 >= 0.5，则舍入行为与 ROUND_UP 相同;否则舍入行为与 ROUND_DOWN 相同。

注意，这是我们大多数人在小学时就学过的舍入模式(四舍五入)。

6、ROUND_HALF_DOWN

向“最接近的”数字舍入，如果与两个相邻数字的距离相等，则为上舍入的舍入模式。

如果舍弃部分 > 0.5，则舍入行为与 ROUND_UP 相同;否则舍入行为与 ROUND_DOWN 相同(五舍六入)。

7、ROUND_HALF_EVEN    银行家舍入法

向“最接近的”数字舍入，如果与两个相邻数字的距离相等，则向相邻的偶数舍入。

如果舍弃部分左边的数字为奇数，则舍入行为与 ROUND_HALF_UP 相同;

如果为偶数，则舍入行为与 ROUND_HALF_DOWN 相同。

注意，在重复进行一系列计算时，此舍入模式可以将累加错误减到最小。

此舍入模式也称为“银行家舍入法”，主要在美国使用。四舍六入，五分两种情况。

如果前一位为奇数，则入位，否则舍去。

以下例子为保留小数点1位，那么这种舍入方式下的结果。

1.15>1.2 1.25>1.2

8、ROUND_UNNECESSARY

断言请求的操作具有精确的结果，因此不需要舍入。

如果对获得精确结果的操作指定此舍入模式，则抛出ArithmeticException。

 常用取值四舍五入（ROUND_HALF_UP） ；

因为我们是属于互联网金融行业，所有在进行计算的时候尽量使用ROUND_HALF_EVEN    银行家舍入法