BigDecimal use

Preface ：

When using single and double precision float and double There are errors in the face of tens of millions of decimal degrees in the operation process of , It's not friendly for our project , Regarding this BigDecimal Can solve the problem well BigDecimal Class provides arithmetic , Zoom operation , Round off , Compare , Hash and format conversion operations .

BigDecimal Use :

ONE // value 1, Scale is 0.

ROUND_CEILING // Round to positive infinity

ROUND_DOWN // Round to zero

ROUND_FLOOR // Round to negative infinity

ROUND_HALF_DOWN // towards （ distance ） The nearest side is rounded , Except on both sides （ Distance of ） It's equal , If so , Round down , for example 1.55 Leave one decimal place and the result is 1.5

ROUND_HALF_EVEN // towards （ distance ） The nearest side is rounded , Except on both sides （ Distance of ） It's equal , If so , If the number of reserved digits is odd , Use ROUND_HALF_UP, If it's even , Use ROUND_HALF_DOWN

ROUND_HALF_UP // towards （ distance ） The nearest side is rounded , Except on both sides （ Distance of ） It's equal , If so , Round up , 1.55 Leave one decimal place and the result is 1.6

ROUND_UNNECESSARY // The results are accurate , There's no rounding pattern

ROUND_UP // To stay away from 0 Rounding in the direction of

Because we use two decimal places , You need to set the last two digits

BigDecimal(double val, MathContext mc) 
// take  double Convert to  BigDecimal , Rounding according to context settings . 

BigDecimal(double val)  // take  double Convert to  BigDecimal , This is a  double The exact decimal representation of the binary floating-point value of . 

Converted in this way BigDecimal object , The final value obtained is different from the value we want, such as ：

BigDecimal d1 = new BigDecimal(0.6);

The output value is ：

0.59999999999999997779553950749686919152736663818359375

And for String The type and int There is no such problem for the numerical value of type , So try to use String The type and int Type conversion value

In the use of BigDecimal When adding, it appears as 0 The situation of

BigDecimal sum= new BigDecimal("0");
sum.add(entity.getB_points_available());

This is because in the bigdecimal During the operation, the result will not be given to the object of the original operation, but to the newly generated object , So use another object to receive values

sum=sum.add(entity.getB_points_available());