Question

Evening,
I’m trying to create a timestamp for when an entity is added to my PriorityQueue using the following SimpleDate format: [yyyy/MM/dd – hh:mm:ss a] (Samples of results below)
Nano-second precision NOT 100% necessary

1: 2012/03/09 – 09:58:36 PM

Do you know how I can maintain an ‘elapsed time’ timestamp that shows when customers have been added to the PriorityQueue?

In the StackOverflow threads I’ve come across, most say to use System.nanoTime(); although I can’t find resources online to implement this into a SimpleDateFormat. I have also consulted with colleagues.

Also, I apologize for not using syntax highlighting (if S.O supports it)

Code excerpt [unused methods omitted]:

 <!-- language: java -->
 package grocerystoresimulation;
 /*****************************************************************************
 * @import
 */
 import java.util.PriorityQueue;
 import java.util.Random;
 import java.util.ArrayList;
 import java.util.Date;
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 /************************************************************************************
 public class GroceryStoreSimulation {
 /************************************************************************************
 * @fields 
 */
    private PriorityQueue<Integer> pq = new PriorityQueue<Integer>();
    private Random rand = new Random(); //instantiate new Random object

    private Date date = new Date();
    private DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd - hh:mm:ss a"); 
    private ArrayList<String> timeStamp = new ArrayList<String>(); //store timestamps

    private int customersServed; //# of customers served during simulation
/************************************************************************************
 * @constuctor
 */
    public GroceryStoreSimulation(){
        System.out.println("Instantiated new GroceryStoreSimulation @ ["
                + dateFormat.format(date) + "]\n" + insertDivider());

        //Program body
        while(true){
            try{
                Thread.sleep(generateWaitTime()); 
                newCustomer(customersServed);
            } catch(InterruptedException e){/*Catch 'em all*/}
        }
    } 
/************************************************************************************
 * @param String ID
 */ 
   private void newCustomer(int ID){
       System.out.println("Customer # " + customersServed + " added to queue. . .");
       pq.offer(ID); //insert element into PriorityQueue
       customersServed++;
       assignArrivalTime(ID); //call assignArrivalTime() method
   } //newCustomer()
/************************************************************************************
 * @param String ID 
 */
   private void assignArrivalTime(int ID){
       timeStamp.add(ID + ": " + dateFormat.format(date));
       System.out.println(timeStamp.get(customersServed-1));
   } //assignArrivalTime()
/************************************************************************************ 
 * @return int 
 */
   private int generateWaitTime(){
       //Local variables
       int Low = 1000;  //1000ms
       int High = 4000; //4000ms
       int waitTime = rand.nextInt(High-Low) + Low;
       System.out.println("Delaying for: " + waitTime); 
       return waitTime;
   }
//***********************************************************************************
   private static String insertDivider(){
       return ("******************************************************************");
   }
//***********************************************************************************
} //GroceryStoreSimulation

Problem:

• Timestamp does not update, only represents initial runtime (see below)
  • Delaying by 1-4 seconds w/Thread.sleep(xxx) (pseudo-randomly generated)
  • Problem may be in the assignArrivalTime() method

Output:

run:
Instantiated new GroceryStoreSimulation @ [2012/03/09 - 09:58:36 PM]
******************************************************************
Delaying for: 1697
Customer # 0 added to queue. . .
0: 2012/03/09 - 09:58:36 PM
Delaying for: 3550
Customer # 1 added to queue. . .
1: 2012/03/09 - 09:58:36 PM
Delaying for: 2009
Customer # 2 added to queue. . .
2: 2012/03/09 - 09:58:36 PM
Delaying for: 1925
BUILD STOPPED (total time: 8 seconds)

Thank you for your assistance, I hope my question is clear enough & I`ve followed your formatting guidelines sufficiently.

Answer 1

You have to use a new instance of Date everytime to get most recent timestamp.

private void assignArrivalTime(int ID){
    timeStamp.add(ID + ": " + dateFormat.format(date)); 
------------------------------------------------^^^^

Try replacing date by new Date() in above line.