Object Oriented Design/How to set up class structure

Question

I am fairly new to object oriented programming and I am curious to know at a high level how to solve this problem.

If I have a list of different calendars i.e. work calendar, personal calendar, sports calendars, etc and each of them have there own respective events. I assume I would have a calendar class and then the nested class would be the event class. Since I want to display all of the events from all the calendars on one list they would all go into on sorted array. But lets say I wanted to delete one of my calendars like my work calendar how would I ensure that all the work events were deleted from this list/array. I am curious to how this class structure would be set up at a high level. Any help would be greatly appreciated.

Answer 1

If I am to do your requirement, I will have the following line up :

interface Calendar 
class DefaultCalendar implements Calendar //<- default implementation for calendar. will hold the implementation for the common behavior for all the calendars
class PersonalCalendar implements Calendar //<- implementation for calendar that holds personal events, decorator for DefaultCalendar
class SportsCalendar implements Calendar //<- implementation for calendar that holds sports events, decorator for DefaultCalendar
class WorkCalendar implements Calendar //<- implementation for calendar that holds work events, decorator for DefaultCalendar
class Event //<- the event object, setters & getters
class CalendarManager //<- object for adding, removing calendars

I will use TreeMap which is an implementation of SortedMap to utilise the natural order of the events to be put.

Map<String, Calendar> calendars = new TreeMap<String, Calendar>();

I will also prepend the event names with words specific to the calendar to group the events by calendar type (thus, event type) when displaying

@Override public void addEvent(Event event){
    //event.setName("Work Event : " + event.getEventName()); for work event
    //event.setName("Sports Event : " + event.getEventName()); for sports event
    //event.setName("Personal Event : " + event.getEventName()); for personal event
    calendar.addEvent(event);
}

Thus, when the manager is asked to display all the events, will result to

Personal Event : blah blah blah abc 123
Personal Event : blah blah blah abc 123
Sports Event : blah blah blah abc 123
Work Event : blah blah blah abc 123

Now, to demonstrate what I'm saying, here are my runnable codes

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.TreeMap;

/* the demo class */

public class CalendarDemo {
    public static void main(String[] args) throws ParseException{
        CalendarManager manager = new CalendarManager();

        Calendar mySportsCalendar = new SportsCalendar(new DefaultCalendar());
        Calendar myWorkCalendar = new WorkCalendar(new DefaultCalendar());
        Calendar myPersonalCalendar = new PersonalCalendar(new DefaultCalendar());

        Event myBirthday = new Event("My 23rd Birthday Celebration", "September 17, 2013", "This marks my 23rd birthday celebration!");
        Event myMothersBirthday = new Event("My Mother's 50th Birthday Celebration", "December 19, 2013", "This marks my mothers 50th birthday celebration!");

        Event tennisGame = new Event("Tennis Game With Denver", "August 11, 2013", "3rd tennis game with my nephew.");

        Event newProjectMeeting = new Event("New Project Meeting", "August 11, 2013", "Meeting with our new project.");

        myPersonalCalendar.addEvent(myBirthday);
        myPersonalCalendar.addEvent(myMothersBirthday);
        myWorkCalendar.addEvent(newProjectMeeting);
        mySportsCalendar.addEvent(tennisGame);

        manager.addCalendar("sportsCalendar", mySportsCalendar);
        manager.addCalendar("workCalendar", myWorkCalendar);
        manager.addCalendar("personalCalendar", myPersonalCalendar);

        System.out.println("Before the removal of personal calendar : ");
        System.out.println("--------------------------------------------------------------------------------");
        System.out.println(manager.displayAllCalendarEvents());

        manager.removeCalendar("personalCalendar"); //<- will delete all the events in personalCalendar;

        System.out.println("After the removal of personal calendar : ");
        System.out.println("--------------------------------------------------------------------------------");
        System.out.println(manager.displayAllCalendarEvents());
    }
}

/* the calendar interface */

interface Calendar{
    Event getEvent(String eventName);
    List<Event> getEvents();
    void addEvent(Event event);
    String getDescription();
    void setDescription(String desc);
}

/* the default implementation of calendar */

class DefaultCalendar implements Calendar{

    private List<Event> events;
    private String description;

    public DefaultCalendar(){
        events = new ArrayList<Event>();
    }

    @Override public Event getEvent(String eventName) {

        for(Event event : events){
            if(event.getEventName().equals(eventName))
                return event;
        }

        throw new IllegalArgumentException("Event name does not exist in the event list.");
    }

    @Override public void addEvent(Event event) {
        events.add(event);
    }

    @Override public String getDescription(){
        return description;
    }

    @Override public void setDescription(String desc){
        description = desc;
    }

    @Override public List<Event> getEvents() {
        return events;
    }
}

/* decorators for defaultcalendar. If you want
 * specific behavior for a specific calendar, you can
 * specify it in these classes.
 * ---------------------------------------------- */

class SportsCalendar implements Calendar{

    private Calendar calendar;

    public SportsCalendar(Calendar baseCalendar){
        calendar = baseCalendar;
    }

    @Override public String getDescription(){
        return calendar.getDescription();
    }

    @Override public void addEvent(Event event){
        event.setEventName("Sports Event : " + event.getEventName());
        calendar.addEvent(event);
    }

    @Override public Event getEvent(String eventName) {
        return calendar.getEvent("Sports Event : " + eventName);
    }

    @Override public void setDescription(String desc) {

        //do something to the passed desc
        //...
        //then pass it to the wrapped calendar;

        calendar.setDescription(desc);
    }

    @Override public List<Event> getEvents() {
        return calendar.getEvents();
    }
}

/* another decorator */

class WorkCalendar implements Calendar{

    private Calendar calendar;

    public WorkCalendar(Calendar baseCalendar){
        calendar = baseCalendar;
    }

    @Override public String getDescription(){
        return calendar.getDescription();
    }

    @Override public void addEvent(Event event){
        event.setEventName("Work Event : " + event.getEventName());
        calendar.addEvent(event);
    }

    @Override public Event getEvent(String eventName) {
        return calendar.getEvent("Work Event : " + eventName);
    }

    @Override public void setDescription(String desc){

        //do something to the passed desc
        //...
        //then pass it to the wrapped calendar;

        calendar.setDescription(desc);
    }

    @Override public List<Event> getEvents() {
        return calendar.getEvents();
    }
}

/* another decorator */

class PersonalCalendar implements Calendar{

    private Calendar calendar;

    public PersonalCalendar(Calendar baseCalendar){
        calendar = baseCalendar;
    }

    @Override public String getDescription(){
        return calendar.getDescription();
    }

    @Override public void addEvent(Event event){
        event.setEventName("Personal Event : " + event.getEventName());
        calendar.addEvent(event);
    }

    @Override public Event getEvent(String eventName) {
        return calendar.getEvent("Personal Event : " + eventName);
    }

    @Override public void setDescription(String desc) {

        //do something to the passed desc
        //...
        //then pass it to the wrapped calendar;

        calendar.setDescription(desc);
    }

    @Override public List<Event> getEvents() {
        return calendar.getEvents();
    }
}

/* the calendar manager, for adding & removing calendars */

class CalendarManager{

    private Map<String, Calendar> calendars;

    public CalendarManager(){
        calendars = new TreeMap<String, Calendar>();
    }

    public void addCalendar(String key, Calendar calendar){
        calendars.put(key, calendar);
    }

    public void removeCalendar(String key){
        calendars.remove(key);
    }

    public String displayAllCalendarEvents(){
        StringBuilder bdr = new StringBuilder();

        for(String key : calendars.keySet()){
            for(Event event : calendars.get(key).getEvents()){
                bdr.append(event.getEventName())
                .append("\t")
                .append(event.getEventDate())
                .append("\t")
                .append(event.getEventDescription())
                .append("\n");
            }
        }

        return bdr.toString();
    }
}

/* the event object */

class Event{

    private String name;
    private Date date;
    private String description;

    public Event(String name, String date, String description){
        this.name = name;
        try {
            this.date = new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH).parse("December 19, 2013");
        } catch (ParseException e) {
            throw new IllegalArgumentException("Invalid date format!");
        }
        this.description = description;
    }

    public String getEventName() {
        return name;
    }

    public Date getEventDate() {
        return date;
    }

    public String getEventDescription() {
        return description;
    }

    public void setEventName(String name) {
        this.name = name;
    }

    public void setEventDate(String date) {
        try {
            this.date = new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH).parse("December 19, 2013");
        } catch (ParseException e) {
            throw new IllegalArgumentException("Invalid date format!");
        }
    }

    public void setEventDescription(String description) {
        this.description = description;
    }
}