JavaBeans samt Serialisierung und Mechanismus für Property-Change Handling

    public void setName(String newName) throws BadParamException {
        if (newName == null || newName.isBlank()) {
            throw new BadParamException(String.format("new '%s' null or blank: '%s'",
                   PROP_NAME, newName));
        }
        String oldName = this.name;
        this.name = newName;
        pcs.firePropertyChange(PROP_NAME, oldName, newName);
    }

    public void addPropertyChangeListener(PropertyChangeListener aspirant) {

        for (PropertyChangeListener listener : pcs.getPropertyChangeListeners()) {
            if (listener.equals(aspirant)) {
                System.out.format("WARNING: listener %s already included", aspirant);
                return;
            }
        }
        pcs.addPropertyChangeListener(aspirant);
    }

    public void removePropertyChangeListener(PropertyChangeListener leaver) {
        pcs.removePropertyChangeListener(leaver);
    }

    public void add(Employee employee) throws BadParamException {
        if (employee == null) {
            throw new BadParamException("mitarb null");
        }
        if (employeesMap.containsKey(employee.getSocSecNr())) {
            throw new BadParamException(String.format("mitarb with SozVersNr %s already in map",
                    employee.getSocSecNr()));
        }
        employeesMap.put(employee.getSocSecNr(), employee);
        employee.addPropertyChangeListener(this);
    }

    public Employee remove(SocSecNr ssnr) {
        Employee removed = null;
        if (employeesMap.containsKey(ssnr)) {
            removed = employeesMap.remove(ssnr);
            removed.removePropertyChangeListener(this);  //removed is not member if Company any more
        }
        return removed;
    }

    // ...

    @Override    // von interface 'PropertyChangeListener'
    public void propertyChange(PropertyChangeEvent evt) {
        System.out.format("changed object: %s%n", evt.getSource());
        System.out.format("  changed Prop: %s%n", evt.getPropertyName());
        System.out.format("  oldValue:     %s%n", evt.getOldValue());
        System.out.format("  newValue:     %s%n", evt.getNewValue());
        System.out.println();

        //NOW e.g. do new sorting, since sort criteria could be affected by change, etc.
        if (evt.getSource() instanceof Employee) {  // if more subclasses or interfaces ...
            if (evt.getPropertyName().equals(Employee.PROP_BIRTHDATE)) {
                printEmployeesSorted("new list after birthDate change", allEmployees(),
                        new Employee.AgeComparator());
            }

            Employee emp = (Employee) evt.getSource(); // much easier with Java-17 !!
            if (emp.getGender() == Gender.FEMALE
                    && emp.getBirthDate().isBefore(LocalDate.parse("1950-01-01"))) {
                System.out.format("ALARM! great-grandma found?: %s%n%n", emp);
            }
        }
        // More actions depending on object, propname, values, ...

    }