如何遍历嵌套的TreeMap？

Question

I have a set of 3 nested TreeMaps:

TreeMap<DayOfWeek, TreeMap<Court, TreeMap<Time, String>>> keyDay = new TreeMap<DayOfWeek, TreeMap<Court, TreeMap<Time, String>>>();
TreeMap<Court, TreeMap<Time, String>> keyCourt = new TreeMap<Court, TreeMap<Time, String>>();
TreeMap<Time, String> keyTime = new TreeMap<Time, String>();

which store info for bookings. I'm trying to iterate through them using nested while loops to show all the bookings that have been created, but I need a way in the nested whiles to show only the values which relate to the relevant parent.

Here's what I have:

        Iterator listOfDays = keyDay.keySet().iterator();
    Iterator listOfCourts = keyCourt.keySet().iterator();
    Iterator listOfTimes = keyTime.keySet().iterator();
    String output;

    while (listOfDays.hasNext()) {
        DayOfWeek currentDay = (DayOfWeek) (listOfDays.next());
        output += currentDay.toString() + "\n----------\n";
        while (listOfCourts.hasNext()){
            Court currentCourt = (Court) (listOfCourts.next());
            output += currentCourt.toString() + ":\n";
            while (listOfTimes.hasNext()){
                Time currentTime = (Time) (listOfTimes.next());
                String currentName = (String) keyTime.get(currentTime);
                output += currentTime.toString() + " - " + currentName + "\n";
            }
        }

...but as expected (but not wanted), it just iterates through all the entries in each TreeMap til the end.

Can anyone help?

Answer 1

It's not very clear (what are listOfDays, listOfCourts and listOfTimes?), but I guess you need something like this:

for (Map.Entry<DayOfWeek, TreeMap<Court, TreeMap<Time, String>>> dayEntry : keyDay.entrySet()) {
    DayOfWeek currentDay = dayEntry.getKey();
    output += currentDay.toString() + "\n----------\n";
    for (Map.Entry<Court, TreeMap<Time, String>> courtEntry : dayEntry.getValue().entrySet()) {
        Court currentCourt = courtEntry.getKey();
        output += currentCourt.toString() + ":\n";
        for (Map.Entry<Time, String> timeEntry : currentCourt.getValue().entrySet()) {
            Time currentTime = timeEntry.getKey();
            String currentName = timeEntry.getValue();
            output += currentTime.toString() + " - " + currentName + "\n";
        }
    }
}

In short, a map can be viewed as a set of map entries, and you can iterate through this entry set. Each entry has a key and a value. Since the value, in your case, is another map, you can repeat this operation on the value.