What is an efficient and elegant way to add a single element to an immutable set?

Question

I have an immutable set (cast as a Set) that potentially contains many elements. I need a Collection that contains the elements from that set plu

Answer 1

You have three options.

• Use a mutable set.
• Check the element isn't already present, if not create a copy of the set and add an element.
• Create a wrapper set which includes the previous set and the element.

Sometimes a BitSet is a better choice than Set depending on the distribution of your values.