Here you can find the source of createObjectID()
public static long createObjectID()
//package com.java2s; import java.util.concurrent.atomic.AtomicLong; public class Main { private static final AtomicLong iCounter = new AtomicLong(); public static long createObjectID() { return iCounter.addAndGet(1); }//from w ww .j av a 2 s.com }