How to generalize utility function using method references/java 8

Question

I\'ve run into a common situation where i have a list of objects and need to generate a comma separated string with a single property, which are then each surrounded by sing

Answer 1

Stream.map() and Collectors.joining() are your friends here.

companies.stream()
         .map(Company::getId)
         .map(s -> "'" + s + "'")
         .collect(joining(","));

You can create a helper method, but in my judgement the above is succinct enough that it isn't worthwhile:

static  String mapAndJoin(Collection c, Function f){
    return c.stream()
            .map(f)
            .map(s -> "'" + s + "'")
            .collect(joining(","));
}

mapAndJoin(companies, Company::getId);