Gabbendorf

public void printMemberNameIfPresent(List<Member> members, int memberId) {
    members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst()
        .ifPresentOrElse(
            member -> printMemberFullName(member.getFullName()),    // if present, print successful message
            () -> printNoMemberMessage(memberId)                    // if absent, print unsuccessful message
        );
    }

Gabbendorf

public void printMemberNameIfPresent(List<Member> members, int memberId) {
    Optional<Member> maybeMember = members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst();
        
    if (maybeMember.isPresent()) {
        printMemberFullName(maybeMember.get().getFullName());   
    }
}

Gabbendorf

public void printMemberNameIfPresent(List<Member> members, int memberId) {
    members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst()
        .ifPresent(member -> printMemberFullName(member.getFullName()));  // if present, apply the lambda on the value
}

private static void printMemberFullName(String memberFullName) {
    System.out.println(String.format("The member's full name is %s", memberFullName));
}

Gabbendorf

public String nameOfActiveMemberById(List<Member> members, int memberId) {
    Optional<Member> maybeMember = members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst();

        if (maybeMember.isPresent() && maybeMember.get().isActive()) {
            return maybeMember.get().getFullName();
        } else {
            throw new NoActiveMemberException();
        }

Gabbendorf

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 
 } 

Gabbendorf

public String memberNameById(List<Member> members, int memberId) {
    return members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst()               // returns an Optional
        .map(Member::getName)      // transforms the value if present in the Optional
        .orElse("UNKNOWN");        // if the Optional is absent, it returns a default value     
}

Gabbendorf

public String memberNameById(List<Member> members, int memberId) {
    Optional<Member> maybeMember = members.stream()
        .filter(member -> member.getId() == memberId)
        .findFirst();               // returns an Optional
    
    if (maybeMember.isPresent()) {
        return maybeMember.get().getName();
    } else {
        return "UNKNOWN";
    }

Gabbendorf

public String memberNameById(List<Member> members, int memberId) {
	return members.stream()
		.filter(member -> member.getId() == memberId)
		.findFirst()        // returns an Optional
		.get()              // extracts the value out of the Optional
		.getName();
}

Gabbendorf

public Member memberById(List<Member> members, int memberId) {
    List<Member> maybeMembers = members.stream()
        .filter(member -> member.getId() == memberId)
        .collect(Collectors.toList());
    
    if (maybeMembers.size() > 0) {
        return maybeMembers.get(0);
    } else {
        return null;
    }

Gabbendorf

public Member memberById(List<Member> members, int memberId) {
    return members.stream()
        .filter(member -> member.getId() == memberId)
        .collect(Collectors.toList())
        .get(0);
}