Looking for Feedback on My Java Complex Number Class

Overall, it looks pretty good! The implementation is clear and you've made an immutable class, which is great. Here are a couple of suggestions:

First, the 'cbrt' method returning a double seems inconsistent with your other methods, which always return a Complex instance. It might be better to stick to the object-oriented approach.

Second, if you need higher precision in your calculations, consider using Java's BigDecimal class. Just keep in mind that it might slow down your performance a bit, but it could be worthwhile for accuracy. Good luck!

Your class looks solid for a beginner! A couple of things to think about:
First, consider that someone might want to use your class to perform actual complex math. You might want to prioritize implementing methods that take a Complex number directly. For example, you can have a multiply method that accepts a double and just calls the Complex one. Something like this: `public Complex multiply(double other) { return multiply(Complex.of(other)); }`.

Also, instead of directly using 'new Complex()', consider having a static method like `Complex.of(double)`, which is becoming standard in Java. And definitely include equals and hashCode methods; they are essential if you want to use your objects in collections.

Lastly, real and imaginary could be shortened to 'r' and 'i', which would make the mathematical operations cleaner and easier to read. Keep it up!