How to to check decimal part on double?

i would like to know how to get the decimal part of a double. Im trying the following code:

double auxValMin= Double.parseDouble("5.3");
double auxDecimal= auxValMin-floor(auxValMin);
System.out.println(auxDecimal); //I get 0.2999999999999998 instead of 0.3

How can i fix the "0.2999999999999998"?

PS: The code is inside a function.