You can create immutable "builder" with lambda chains. This also gives you the compiletime guarantee that you have specified the required fields (At the cost of flexibility and ease of adding new fields)

http://benjiweber.co.uk/blog/2014/11/02/builder-pattern-with...

Regarding your isPrefixOf - is there a significant benefit to that being in the standard library? You could define a isPrefixedWith("s") that returns a Predicate<String> yourself.