class Topic extends AbstractPersistable {

    private int duration; // in minutes
    private Set<Student> studentSet;

    // Calculated during initialization, not modified during score calculation.
    private boolean frontLoadLarge;
    private Set<Topic> coincidenceTopicSet = null;

    public int getDuration() {
        return duration;
    }

    public void setDuration(int duration) {
        this.duration = duration;
    }

    public Set<Student> getStudentSet() {
        return studentSet;
    }

    public void setStudentSet(Set<Student> studentSet) {
        this.studentSet = studentSet;
    }

    @JsonIgnore
    public int getStudentSize() {
        return studentSet.size();
    }

    public boolean isFrontLoadLarge() {
        return frontLoadLarge;
    }

    public void setFrontLoadLarge(boolean frontLoadLarge) {
        this.frontLoadLarge = frontLoadLarge;
    }

    public Set<Topic> getCoincidenceTopicSet() {
        return coincidenceTopicSet;
    }

    public void setCoincidenceTopicSet(Set<Topic> coincidenceTopicSet) {
        this.coincidenceTopicSet = coincidenceTopicSet;
    }

    public boolean hasCoincidenceTopic() {
        return coincidenceTopicSet != null;
    }

    @Override
    public String toString() {<FILL_FUNCTION_BODY>}

    // ************************************************************************
    // With methods
    // ************************************************************************

    public Topic withId(long id) {
        this.setId(id);
        return this;
    }

    public Topic withDuration(int duration) {
        this.setDuration(duration);
        return this;
    }

    public Topic withStudents(Student... students) {
        this.setStudentSet(Arrays.stream(students).collect(Collectors.toSet()));
        return this;
    }

    public Topic withFrontLoadLarge(boolean frontLoadLarge) {
        this.setFrontLoadLarge(frontLoadLarge);
        return this;
    }

    public Topic withCoincidenceTopicSet(Set<Topic> coincidenceTopicSet) {
        this.setCoincidenceTopicSet(coincidenceTopicSet);
        return this;
    }
}

        return id == null ? "no id" : Long.toString(id);
    
<methods>public long getId() ,public java.lang.String toString() <variables>protected java.lang.Long id