How to multiply a double with a BigInteger in Java

Question

I want to multiply for example; 0.1 * 10^30

How do I achieve this?

0.1 is a double 10^30 is a BigInteger

Human input will be converted into a double value but the value needs to be multiplied by 10^30 for computation.

Human input can be 0.09172349 for example.

Answer 1

Your best bet is to convert both to java.math.BigDecimal .

Please see the caveats and advice at the Javadoc for BigDecimal(double) . You mention "human input"; if you can take that human input directly as-is, and avoid bringing double into the picture at all, then you should.

[…] the value needs to be multiplied by 10^30 for computation.

If you are always multiplying by 10 ³⁰ — that's a fixed constant — then you should use BigDecimal.movePointRight(int) .