MultiThread Syncronisation

Question

Hi,
This is my Thraed program and the output of this program is given below. Can anyone tell how it gave that output? I understand it is syncronisation problem, but trying to understand how it gave that output.
public class TestThread implements Runnable {
     public static int x = 0;
     public void run() {
     x = x 1;
     FileOutputStream fOut = new FileOutputStream("c:/data1.txt", true);
     fOut.write(("Before : x = " x " " "bookingNumber").getBytes());
     fOut.flush();
     fOut.close();
     public void static void main(String [] args) {
          Thread thread = new Thread(new TestThread());
          thread.start();
          thread = new Thread(new TestThread());
          thread.start();
          thread = new Thread(new TestThread());
          thread.start();
CONTENTS OF c:/data1.txt:
Before : x = 1 bookingNumberBefore : x = 1 bookingNumberBefore : x = 2 bookingNumber
w Thread(new TestThread());
          thread.start();
          thread = new Thread(new TestThread());
          thread.start();
CONTENTS OF c:/data1.txt:
Before : x = 1 bookingNumberBefore : x = 1 bookingNumberBefore : x = 2 bookingNumber

Answer 1

Simple synchronization problem, because:
x = x + 1
is getting executed simultaneously (that is, almost simultaneously) by multiple threads, and it is not an "atomic" operation. Thread 1 will get the value of x (0) and start to add 1 to it, while Thread 2 will get the value of x (which is still 0) and start to add 1 to it. Then thread 1 saves the new value into x (now 1), and thread 2 saves the new value into x (which it calculated as 1 as well).