Java Optional: example with .filter() and .map()

memberFinder.java

public String nameOfActiveMemberById(List<Member> members, int memberId) {
    return members.stream()
        .filter(member -> member.getId() == memberId)  // this is stream.filter
        .findFirst()                                   // gets Optional
        .filter(Member::isActive)                      // if present, apply the predicate
        .map(Member::getFullName)                      // if the output of predicate is true, get the full name
        .orElseThrow(NoActiveMemberException::new);    // if the output is false, throw an exception 
 }