1_FieldsObservable.java

public interface FieldsObservable {
    // @param <E>           the type of the Field and FieldObserver to guarantee compatibility
    
    public <E> void addFieldObserver(Field<? extends E> field, FieldObserver<? super E> fieldObserver);
    
    public <E> void removeFieldObserver(Field<? extends E> field, FieldObserver<? super E> fieldObserver);
    
    public <E> void notifyFieldObservers(final Field<E> field, final E data);
}

2_FieldObserver.java

public interface FieldObserver<E> {

    /**
     * To be called when data has changed.
     * @param field the Field-tag of the data
     * @param data the new data
     */
    public void updateData(Field<E> field, E data);

}

3_ConcreteProfile.java

//AbstractFieldsObservable to be replaced by component, will look similar to PropertyChangeListener
public interface Profile extends AbstractFieldsObservable {
    public static final Field<String> FIRST_NAME = new Field("firstName");
    private String firstName;
        
    public void setFirstName(String firstName) {
        this.firstName = firstName;
        notifyFieldObservers(FIRST_NAME, firstName);
    }
}