Trying to keep track of how many objects I create

Question

Hello everyone I'm trying to keep track of how many message objects I created and Assign them to a data member.
Right now it assigns all the Message objects the same number at the end which is 3. I wanted it to assign 1 to the first object it create, 2 for the 2nd, and 3 for the 3rd.
here's a small version of my code:
package ss;
import java.util.ArrayList;
import java.util.Iterator;
public class MainTest {
     public static void main(String [] args)
          Message msg = null;
          ArrayList<Message> msgList = new ArrayList<Message>();
          for(int i = 0; i < 3; i++)
               msg = new Message();
               msgList.add(msg);
          System.out.println(msgList);
package ss;
//this class will hold the Event/Message
import java.util.List;
import java.util.HashMap;
import java.util.Map;
import java.util.ArrayList;
import java.util.Set;
import java.util.Iterator;
public class Message {
     //these are datamembers that will be used during
     //the sending of the message to the reciever
     //PacketID should be incremented each time a new message is created
     static int PacketID = 0;
     Message()
          PacketID +=1;
     public String toString() {
          return("PacketID: " + this.PacketID
                    + "\n");
}output:
[PacketID: 3
, PacketID: 3
, PacketID: 3
Any ideas what I'm doing wrong?
Thanks!

Answer 1

Thanks BigDaddyLovehandles,
Well there's the problem, I just posted a simpler problem to a bigger one. So I am keeping them in a collection as you can see below.
I'm keeping these message stored in a multi map, and it is multi-threaded. Everytime a user connects to my server I create a new thread, and start adding the "messages" to the database.
But I must have a packetID, meaning every new message created I need to assign that number to the message object.
I also see a problem with this like you said, its not thread safe, if 2 clients connect to the server, and both send me events, there are going to be 2 different maps, copying events from the client and storing them in their own seperate databases.
This might not be a problem because after I get the events on each thread, i send them to another server for processing.
Here's an example of what my database looks like that stores the messages:
//this class should store all the Messages or "Events" and
//you can access them based on their Serial key.
public class MessageDB {
     //database to hold the information
     //     holds the Alerts/messages
     Map<String, List<Message>> AlertMap;
     //Constructor
     MessageDB() {
          AlertMap = new HashMap<String, List<Message>>();
     //print, outputs the contents of the hashMap
     public void print() {
          //want to print out the Key and all the Messages
          //associated with that key
          //print, outputs the contents of the hashMap
               for (String key : AlertMap.keySet())
                    System.out.println("\n\nSerial (key): " + key
                              + "\nValues in Map: \n" + AlertMap.get(key));
     void add(Message msg) {
          //getting the position of the List by EntityID if avaiable
          List<Message> AlertList = AlertMap.get(msg.Serial);
          //checking to see if there is a unique Key already in the Map.
          if (AlertList == null) {
               //if there isnt a key in the map, add a new key, and a new List mapping
               //to the key EntityID;
               AlertList = new ArrayList<Message>();
               AlertMap.put(msg.Serial, AlertList);
               AlertList.add(msg);
          } else {
               //adding message to List
               AlertList.add(msg);
     }Any suggestions on what I can to number all these messages and it will be thread safe?