使用什么数据结构？

Question

I need to represent the below data (in Java):

• 2012 (Year)
  • 01(Month)
    • 01 (Day)
      • Hello I am a string
    • 02
    • ...
  • 02
  • 03
  • 04
  • …

I was thinking of using a TreeMap, but not sure how. Any ideas?

Answer 1

Considerations, assuming you're interested in managing calendar entries :

• There are infinite possible dates -- don't waste memory on unused days
• Given a date, you'd want to access it's day quickly -- use array or hash-based lookup
• Each day has a unique date -- map date => day

THE MODEL

// best to use ENUM for fixed set of constants
enum Month {
    JANUARY, FEBRUARY, ... , NOVEMBER, DECEMBER
}

enum Weekday {
    SUNDAY, MONDAY, ... , FRIDAY, SATURDAY
}

/**
 * The day "data node". Fill in constructors/accessors.
 */
class Day {
    int year;
    Month month;
    Weekday weekday;
    String date; // hashkey
    String entry; // the entry
}

/**
 * The calendar, simply mapping a unique date to it's day.
 * Create a date like: year + "-" + MONTH + "-" + DAY
 */
HashMap<String, Day> calendar;

THE VIEW
Since our data structure is not sparse, an independent view would have to simulate a full calendar. Display all days/generate all dates according to the rules of calendars, but only add a day to the HashMap if a new entry is saved.

NOTES

• Pretty efficient in space and time.
• Above is over-simplified: wrap the HashMap in a class to arbitrate CRUD operations on days .
• Assumes you don't need to manipulate months/years but only days. If this is wrong, and you'd like to eg get all days in a month , or delete a year , consider having a three-level map like year => month => day alongside above.

Answer 2

JTree from Swing can also be used as data structure.

But the first question you should ask yourself is "How I want to access the data".

Answer 3

You would need some sort of tree structure. This might be your starting point:

public class Node {
    private String label;
    private List<Node> children;
    //add Constructors, getters, setters, and member methods, etc
}


Node root = new Node();
root.setLabel("2012");
//children of root are "01", "02", etc.

Answer 4

Definitely separate model data from view data.

Here is a different model than the one proposed in the paislee answer.

Map<Calendar, String> thisIsAllYouNeedForTheModel = new HashMap<Calendar, String>();
Calendar thisIsTheKey = Calendar.getInstance();

thisIsTheKey.clear();
thisIsTheKey.set(Calendar.YEAR, theYear);
thisIsTheKey.set(Calendar.MONTH, theMonth);
thisIsTheKey.set(Calendar.DAY_OF_MONTH, theMonth);
thisIsTheKey.set(Calendar.HOUR, theHour);
thisIsTheKey.set(Calendar.MINUTE, theMinute);
thisIsTheKey.set(Calendar.SECOND, theSecond);
thisIsAllYouNeedForTheModel.put(thisIsTheKey, data);

Edit: silly me. Map<Calendar, String> is my suggestion.

Answer 5

I would suggest the TreeMap, but if you want to make experiments, just go ahead and use LinkedList. Acessing the data is pretty complex if you iterate through many lists. But it was a lot of fun experimenting.

EDIT: Here is a tutorial including a package that allows you to use a TreeMap or something similiar to a Tree: http://code.google.com/p/qed-java/wiki/HowToUseTree