Filtering Java Nested List-CodePudding

I've a school list which contains class, class list which also contains student and student are also another list. I want to apply two nested filter which first will check that if any class have a empty student list and second filter is for checking that if school has any empty class list and finally it should return the list but I just can't apply two filters as nested, I keep getting syntax error. I'm a bit new to stream api.

result = result.stream()
          .filter(school -> school.getSchoolClassList().stream()
                    .filter(schoolClass-> schoolClass.getStudentList().stream()
                    .anyMatch(schoolClass-> schoolClass.getStudentList().size() > 0))
          .anyMatch(school -> school.getSchoolClassList().size() > 0))
          .collect(Collectors.toList());

CodePudding user response：

You might want to add the resulting Syntax error. However, as I see at first is, that you are using class as an identifier, when it is actually a reserved keyword in Java programming language. Consider renaming the identifiers to something alike schoolClass.

CodePudding user response：

I am not sure if I understood you correctly but as far as I got it is that you want to get all schools that either have empty classes or that have classes without students.

What you can do is defining the predicates outside of the stream.

Predicate<School> empty_students_filter = school ->
    school.getSchoolClassList().stream().map(SchoolClass::getStudentList).anyMatch(List::isEmpty);

Predicate<School> empty_classes_filter = school -> school.getSchoolClassList().isEmpty();

Then you can use the predicates inside your filter method and combine them with Predicate.or():

List<School> schools_with_no_or_empty_classes = 
    schools.stream()
           .filter(empty_classes_filter.or(empty_students_filter))
           .collect(Collectors.toList());

Note: if you want to get only the schools that have classes and all classes should have students, then you can adapt the filter as follows with a Predicate.and():

.filter(Predicate.not(empty_classes_filter).and(Predicate.not(empty_students_filter)))