filtering of values in list based on values in set

marti6addams :

I'm trying to use java 8 to solve the following issue. Say I have the following (A and B are custom classes)

ArrayList<A> skills;
HashSet<B> workCenters;

What I need to do is to find whether value a.getDepartment() which is a String also contained in B which also has a method String getDepartment() and then to collect those into new List<A>.

I tried such:

 List<A> collect = skills.stream()
     .filter(s -> workCenters.contains(s.getDepartment())
     .collect(Collectors.toList());

but in this case i don't do it right because I couldn't retrieve getDepartment() from workCenters. What would be the correct solution?

ernest_k :

You could start with converting HashSet<B> to HashSet<String> and then use your code:

Set<String> bDeps = workCenters.stream()
                               .map(B::getDepartment)
                               .collect(Collectors.toSet());

List<A> collect = skills.stream()
                         .filter(s -> bDeps.contains(s.getDepartment()))
                         .collect(Collectors.toList());