Sorting TreeMap

Question

Hi,
I've been trying to work this out and can't seem to find a solution. I have a treemap of object and I want to sort them by their names, such as lastname. These object hold all these datas. I wrote myself a comparator class like this:
import java.util.*;
import java.io.*;
public class PatientComparator implements Comparator {
public int compare(Object obj1, Object obj2) throws ClassCastException {
System.out.println(obj1.getClass()); //use to see what is passing in to compare
Patient a = (Patient)obj1;
Patient b = (Patient)obj2;
String nameA = a.getName();
String nameB = b.getName();
String firstName = nameA.substring(0,nameA.indexOf(",",0)-1);
String lastName = nameA.substring(nameA.indexOf(",",0)+1,nameA.length()-1);
String firstName2 = nameB.substring(0,nameB.indexOf(",",0)-1);
String lastName2 = nameB.substring(nameB.indexOf(",",0)+1,nameB.length()-1);
int result = 0;
if ( !(lastName.equals(lastName2)) )
     result = lastName.compareTo(lastName2);
else
result = firstName.compareTo(firstName2);
return result;
I have to use TreeMap or HashMap right now because they both utilize the assigned key to identify object quicker. But the culprit is how do I sort this TreeMap in term of object properties(like name, age). Here is the class I implement it:
public class DoctorsOffice {
private String office_name;
private int ID = 1000; //start out with id # 1000
private SortedMap active = new TreeMap(new PatientComparator());
//private SortedSet inactive = new TreeSet();
* Constructor for a DoctorsOffice object.
* @param name Name of this Dr's Office
public DoctorsOffice (String name) {
office_name = name;
* Add a new patient to the office. The identification
* number is uniquely generated and is returned when the
* Patient object is added to the database. ID numbers
* start at 1000 and increment by one for each new Patient
* added.
* @param firstName first name of this patient
* @param lastName last name of this patient
* @param age age of this patient
* @return the ID number assigned to this Patient
public int addPatient (String firstName, String lastName, int age) {
Patient new_patient = new Patient( firstName,lastName,age );
active.put( new Integer(ID), new_patient );
ID++;
return (ID - 1);
* Remove this patient from the master database. Removed patients are
* archived in an "inactive" database which maintains Patron
* objects in the order in which they were removed from the master
* database.
* @param patientNo     Patient number assigned
* @exception throws a NoSuchPatientException
* if this patient does not exist
public void removePatient (int patientNo)
throws NoSuchPatientException {
* Add a new medication for this patient.
* @param patientNo     Patient number
* @param medicationName     Name of this medication
* @param isGeneric     True if a generic drug
* @exception throws NoSuchPatientException if
* this patient ID does not exist.
public void addMedication(int patientNo, String medicationName,
     boolean isGeneric ) throws NoSuchPatientException {
if ( active.containsKey(new Integer(patientNo)) ) {
((Patient)active.get(new Integer(patientNo))).recordNewMed(
medicationName, isGeneric );
else
     throw new NoSuchPatientException();
* Print the medication detail for this patient. Print
* the patient's full name (lastname COMMA SPACE firstName)
* then each medication (each one on a new line). To print
* the medications, simply call your toString() method in
* the Medication class.
* If this patient has no medication history, print "No Medications
* Prescribed".
* @param patientNo     Patient number
* @exception throws NoSuchPatientException
* if patient does not exist.
public void printMedicationDetail (int patientNo)
     throws NoSuchPatientException {
Integer patientID = new Integer(patientNo);
if ( active.containsKey(patientID) ) {
System.out.println( ( (Patient)active.get(patientID)).getName() );
((Patient)active.get(patientID)).printMedicationHistory();
else
throw new NoSuchPatientException();
* Print all patients ordered by last name, then first name if
* you encounter two patients with the same last name.
* To print the Patient objects, simply call your toString() method
* in the Patient class.
public void listByName() {        
     // Collection coll = active.values();
// List temp = new ArrayList(coll);
     // sort(temp,new PatientComparator());
// Set s = temp.keySet();
Iterator iterator = active.iterator();
while( iterator.hasNext() ){
     // String key = (String)iterator.next();     
     System.out.println(iterator.next());     
}

Answer 1

I guess I go with the easiest way to do it. But here's
another culprit, since values() method turn my
TreeMap into a collection(interface), It doesn't turn the TreeMap into anything. That is, the original TM still exists, exactly as you left it. There's just a new Collection created that refers to each of the TM's values.
and the sort()
method is in class Collections, how do I call the
sort(), and also the sort() method has two parameters
(List list, Comparator C)If your values implement Comparable, and you want to use the natural sort order (for instance, the values are Strings and you just want them sorted alphabetically), then you just call the sort method that takes a single List parameter. Otherwise (for instance, you want to reverse the sort order, or sort by length, etc.), you have to write a Comparator for your values.
>
1st) I don't have any list to put as parameter.Both LinkedList and ArrayList take a Collection as a constructor arg, I think, so you can construct one from the Collection returned by values().
2nd) Comparator C will keep comparing two keys from
the treemap or in the collection?
Collection coll = active.values();
Collections.sort( , new
PatientComparator());The TreeMap's Comparator will do that. The values List will sort however you tell it to, regardless of how the TreeMap sorts its keys.
I don't think the sort is able to be called this way,
and what do I substitute in for a parameter list when
I have a treemap right now? Huh?