[Turn] BigDecimal use (finishing)

Original Address: https: //www.jianshu.com/p/2947868d76eb

Scenarios

Most business computing, the general class java.math.BigDecimal accurate calculation. For example: Money

use

1, constructed BigDecimal

BigDecimal BigDecimal(double d); //不允许使用,精度不能保证 BigDecimal BigDecimal(String s); //常用,推荐使用 static BigDecimal valueOf(double d); //常用,推荐使用 

2, method

method	Miao Xu
add(BigDecimal)	BigDecimal object values ​​are added, and then return the object
subtract(BigDecimal)	Value BigDecimal object subtraction, and return the object
multiply(BigDecimal)	BigDecimal object value is multiplied, and then return the object
divide(BigDecimal)	BigDecimal object divided by the value, and then return the object
toString()	BigDecimal to convert the value into a string object
doubleValue()	The value returned BigDecimal object to double the number of
floatValue ()	The value returned BigDecimal object to single precision
long value ()	The value returned BigDecimal object to a long integer
intValue()	The value returned BigDecimal object to an integer.

3, formatting and rounding

// 格式化：保留2为小数
DecimalFormat df = new DecimalFormat("#.##");
// 四舍五入，默认五舍六入
df.setRoundingMode(RoundingMode.HALF_UP);

4, formatting
DecimalFormat analysis:

symbol	position	Miao Xu
0	digital	Arabic numerals, if there is displayed 0
#	digital	Arabic numerals, if there is no display 0
.	digital	Decimal separator or monetary decimal separator
,	digital	Packet delimiter
E	digital	Partition mantissa and exponent in scientific notation. In the prefix or suffix Need not be quoted.
-	digital	negative
;	Sub-mode boundary	Partition positive and negative subpatterns
%	Prefix or suffix	Multiplied by 100 and is displayed as a percentage
\u2030	Prefix or suffix	Multiply by 1000 and show as per mille
¤ (\ U00a4)	Prefix or suffix	Currency sign, replaced by currency symbol. If both occur simultaneously, replaced by international currency symbol. If present in a pattern, the monetary decimal separators, instead of the decimal separator.
'	Prefix or suffix	A prefix or suffix to quote special characters, such as " '#' #" formats 123 "# 123." To create a single quote itself, use two in single quotation marks: "# o''clock".

5, the rounding mode Introduction

• RoundingMode.CEILNG: The general direction toward positive infinity rounding rounding mode. If the result is positive, the rounding behavior is similar RoundingMode.UP; if the result is negative, the rounding behavior is similar to RoundingMode.DOWN
  the following:

5.5  =>  6 
1.1  =>  2
-1.0 => -1 -2.5 => -2 

• RoundingMode.DOWN: Towards zero rounding mode rounding. Never dropped off the front of the number plus 1 (i.e. censored). Note that this rounding mode never increases the calculated value of the absolute values
  are as follows:

5.5  =>  5 
1.1  =>  1 
-1.0 => -1 -1.6 => -1 

• RoundingMode.FLOOR: The general direction toward negative infinity rounding rounding mode. If the result is positive, the rounding behavior is similar to RoundingMode.DOWN; if the result is negative, the rounding behaves like RoundingMode.UP
  注意：此舍入模式始终不会增加计算值
  as follows:

5.5  =>  5 
2.3  =>  2
1.0 => 1 -1.1 => -2 -2.5 => -3 

• RoundingMode.HALF_DOWN: the closest to the direction of rounding numbers rounding mode, if the numbers are equal to the distance of two adjacent, rounded down. If the discarded fraction is> 0.5, the rounding behavior with RoundingMode.UP; otherwise the same rounding behavior RoundingMode.DOWN;
  五舍六入
  follows:

2.5  =>  2 
1.6  =>  2
-1.1 => -1 -1.6 => -2 -2.5 => -2 

• RoundingMode.HALF_EVEN: the closest to the direction of rounding numbers rounding mode, if the numbers are equal distance from two adjacent, the adjacent even to rounding. If the number is odd part left of the discarded, the rounding behavior with RoundingMode.HALF_UP; if even, then rounding behavior with RoundingMode.HALF_DOWN. Note that when repeating a series of calculations, the rounding mode that minimizes cumulative error in the statistics on. This rounding mode is also known as the "banker's rounding method", mainly in the United States. This rounding mode is similar to the Java float and double strategy rounding algorithm used
  is as follows:

5.5  =>  6 
2.5  =>  2 
1.1 => 1 -1.0 => -1 -1.6 => -2 -2.5 => -2 

• RoundingMode.HALF_UP: the closest to the direction of rounding numbers rounding mode, if the numbers are equal to the distance of two adjacent, rounded up. If the discarded fraction is> = 0.5, the rounding behavior with RoundingMode.UP; otherwise RoundingMode.DOWN rounding behavior with
  注意：此舍入模式就是通常学校里讲的四舍五入
  the following:

2.5  =>  3 
1.1  =>  1 
-1.1 => -1 -1.6 => -2 

• RoundingMode.UNNECESSARY: for asserting the requested operation with accurate results rounding mode, hence no rounding. If the designated rounding mode to generate precise operation result is thrown ArithmeticException
  follows:

1.5  =>  抛出 ArithmeticException
1.1  =>  抛出 ArithmeticException
1.0  =>  1
-1.1 =>抛出 ArithmeticException -1.6 => 抛出 ArithmeticException 

• RoundingMode.UP: rounding away from zero rounding mode. Always in front of the digital non-zero discarded fraction plus one. Note that this rounding mode does not reduce the absolute value calculated
  as follows:

5.5  =>  6 
1.1  =>  2 
-1.1 => -2 -1.6 => -2 

problem

1. When BigDecimal divide method is not divisible when dividing, it occurs when the infinite decimal, it will throw an abnormality, the abnormality as follows: java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result at java.math.BigDecimal. .divide (Unknown Source)

Solution: Set accurate to divide the decimal point

JavaMoney (third party)

Java 9 in New Currency API