Java > Threads > Static synchronize

public class StaticSync extends Object {
  private static int nextSerialNum = 10001;

  public static synchronized int getNextSerialNum() {
    int sn = nextSerialNum;

    try { Thread.sleep(1000); } 
    catch ( InterruptedException x ) { }

    nextSerialNum++;
    return sn;
  }

  private static void print(String msg) {
    String threadName = Thread.currentThread().getName();
    System.out.println(threadName + ": " + msg);
  }

  public static void main(String[] args) {
    try {
      Runnable r = new Runnable() {
          public void run() {
            print("getNextSerialNum()=" + 
                getNextSerialNum());
          }
        };
      
      Thread threadA = new Thread(r, "threadA");
      threadA.start();
  
      Thread.sleep(1500); 
  
      Thread threadB = new Thread(r, "threadB");
      threadB.start();
  
      Thread.sleep(500); 
  
      Thread threadC = new Thread(r, "threadC");
      threadC.start();
  
      Thread.sleep(2500); 

      Thread threadD = new Thread(r, "threadD");
      threadD.start();
    } catch ( InterruptedException x ) {
      // ignore
    }
  }
}