import java.util.concurrent.*; 
class Problem { 
   // felles data og metoder A 
   static int num = 3; 
   CyclicBarrier b = new CyclicBarrier(num); 

   public static void main(String [] args) { 
      Problem p = new Problem(); 
      p.utfoer(num+1); // num+1 == 4 
      System.out.println(" Main TERMINATED"); 
   } // end main 

   void utfoer (int antT) { 
      Thread [] t = new Thread [antT]; 
      for (int i =0; i< antT; i++) 
         ( t[i] = new Thread(new Arbeider(i))).start(); 
     try { 
        for (int i =0; i< antT; i++) t[i].join(); 
     } catch(Exception e) {} 
   } // end utfoer 

   class Arbeider implements Runnable {
      // lokale data og metoder B
      int ind;

      void sync() {
         try{
            b.await();
         } catch (Exception e) { return;} 
      }

      public Arbeider (int in) {ind = in;};

      public void run() { 
         // kalles naar traaden er startet
         if (ind == 1) try {
            TimeUnit.SECONDS.sleep(2);
         } catch (Exception e) { return;};
         sync();
         System.out.println("A"+ind); 
         sync();
         System.out.println("B"+ind); 
      } // end run 
   } // end indre klasse Arbeider 
} // end class Problem