java - BigDecimal to string

Question

I have a BigDecimal object and i want to convert it to string. The problem is that my value got fraction and i get a huge number (in length) and i only need the original number in string for example: for

BigDecimal bd = new BigDecimal(10.0001)
System.out.println(bd.toString());
System.out.println(bd.toPlainString());

the output is:

10.000099999999999766941982670687139034271240234375
10.000099999999999766941982670687139034271240234375

and i need the out put to be exactly the number 10.0001 in string

Answer 1

To get exactly 10.0001 you need to use the String constructor or valueOf (which constructs a BigDecimal based on the canonical representation of the double):

BigDecimal bd = new BigDecimal("10.0001");
System.out.println(bd.toString()); // prints 10.0001
//or alternatively
BigDecimal bd = BigDecimal.valueOf(10.0001);
System.out.println(bd.toString()); // prints 10.0001

The problem with new BigDecimal(10.0001) is that the argument is a double and it happens that doubles can't represent 10.0001 exactly. So 10.0001 is "transformed" to the closest possible double, which is 10.000099999999999766941982670687139034271240234375 and that's what your BigDecimal shows.

For that reason, it rarely makes sense to use the double constructor.

You can read more about it here, Moving decimal places over in a double