The Java synchronized keyword is compared with the concurrent and the performance of the contract. __java

private static Atomicinteger mysessionid= new Atomicinteger (-2);     public static int Getmysessionid () {return mysessionid.decrementandget ();     private static int mysessionid=-2;     public static synchronized int Getmysessionid () {return mysessionid--; After opening 300 threads, each thread to do more than 10,000 cycles, found that unexpectedly atomic atomic class unexpectedly higher than the average synchronized almost 3 times times, and the speed is very stable, and synchronized performance is not stable, and speed is also slow.