What will be the output of the program?

 class Happy extends Thread 
 {    
    final StringBuffer sb1 = new StringBuffer(); 
    final StringBuffer sb2 = new StringBuffer();     

  public static void main(String args[])        
  {  
     final Happy h = new Happy();           

     new Thread()   
     {         
        public void run()          
        {                  
          synchronized(this)                  
          {                      
             h.sb1.append("A");                      
             h.sb2.append("B");                      
             System.out.println(h.sb1);                      
             System.out.println(h.sb2);                  
           }       
        }       
     }.start();     
     
     new Thread()      
     {             
         public void run()     
         {                  
            synchronized(this)                  
            {                      
               h.sb1.append("D");                      
               h.sb2.append("C");                      
               System.out.println(h.sb2);                      
               System.out.println(h.sb1);                  
            }            
         }        
      }.start();  
    } 
 }