Java中的mutator方法的最佳实践

Question

I have written a function which sorts ArrayList of custom object Collection.sort.

public List<Student> getStudents(int std) {
    List<Student> students = studentDAO.getStudents(std);
    ......
    sortStudents(students);
    .....
    return students;
}

private void sortStudents(students) {
    Collection.sort(students, new Comparator<Student>(){
        public int compare(Student s1, Student s2) {
            return s1.getDOB().compareTo(s2.getDOB());
        }
    });
}

Is above code is clean? Is it ok to write such mutators or should use a new object and return it?

Answer 1

This depends on the contract of studentDAO.getStudents() method - does it guarantee to always return a new list of results (ie an object that only the caller will have reference to)? If so, then you can safely sort it in place. If not, you should make a copy.

Another concern is - will it always guarantee that? One of many way this can go wrong is if you add some caching - that could easily break this guarantee.