How to get the common field from a list of object

Question

Say I have a class of Student contain in fields : firstName and surname

I then use this to create two lists

List<Student> classroomA = {["Ben","oreilly"], ["Jenna","Birch"]}
List<Student> classroomB = {["Alan","Messing"], ["Ben", "Mancini"], ["Helena","Wong"]}

How would I go about using these lists to get all Students with same name from the list :

List<Student> commonStudents = {["Ben","oreilly"],["Ben", "Mancini"]}

Would doing for loop on both list and doing a classroomA.getfirstName().equals(classroomB.getfirstName()) the only way ?

Answer 1

Use Java 8 Lambdas.

Below code gets all Bens from the list. If you want a particular field from the object (which is transformation), then use the map on filter stream.

  List<Student> AllBens = classA.stream().filter(Objects::nonNull).
         filter(k -> StringUtils.isNotEmpty(k.getName()) && k.getName().equalsIgnoreCase("Ben")).collect(Collectors.toList());