4.java

class SyncThread implements Runnable {

    @Override
    public void run() {
        sync();
    }
    public synchronized void sync() {
        System.out.println(Thread.currentThread().getName() + "_Sync: " + new SimpleDateFormat("HH:mm:ss").format(new Date()));
        try {
            System.out.println(Thread.currentThread().getName() + "_Sync_Start: " + new SimpleDateFormat("HH:mm:ss").format(new Date()));
            Thread.sleep(2000);
            System.out.println(Thread.currentThread().getName() + "_Sync_End: " + new SimpleDateFormat("HH:mm:ss").format(new Date()));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
F_thread2_Sync: 23:26:38
F_thread3_Sync: 23:26:38
F_thread2_Sync_Start: 23:26:38
F_thread3_Sync_Start: 23:26:38
F_thread1_Sync: 23:26:38
F_thread1_Sync_Start: 23:26:38
F_thread3_Sync_End: 23:26:40
F_thread2_Sync_End: 23:26:40
F_thread1_Sync_End: 23:26:40
F_thread4_Sync: 23:26:40
F_thread4_Sync_Start: 23:26:40
F_thread4_Sync_End: 23:26:42