java - How to add a very small number and a very large number -

i pretty new java. learning numerical computation @ moment. how 1 add , multiply small number , large number, of order $10^{-20}$ , of order $10^{20}$ arbitrary precision.

take @ bigdecimal class. javadoc:

immutable, arbitrary-precision signed decimal numbers.

and:

the bigdecimal class gives user complete control on rounding behavior.

for example:

import java.math.bigdecimal;  public class main {     public static void main(string[] args) {         bigdecimal big = new bigdecimal("10e20");         bigdecimal small = new bigdecimal("10e-20");         bigdecimal ans = big.add(small);          system.err.println("answer: " + ans);     } } 

running gives following:

$ java main answer: 1000000000000000000000.00000000000000000010