Desmistificando Threads (DÚVIDA)

public class Threads1 {  
        int x = 0;  
  
        public class Runner implements Runnable {  
            public void run() {  
                synchronized(this){		
            	
                int current = 0;  
                for (int i = 0; i < 4; i++) {  
                    current = x;  
                    System.out.print(current + ", ");  
                   x = current + 2;  
               }  
                notify();
           }  
         }  
      }
        
       public static void main(String[] args) {  
           Threads1 r1 = new Threads1();
           Threads1 r2 = new Threads1();
                     
                     
       synchronized(r1){
    	   try{
    		   System.out.println("Waiting for R1  to complete");
    		  
    	   r1.wait();
    	   }catch(InterruptedException e){}
    	   
      synchronized(r2){
    	  try{
    		  System.out.println("Waiting for R2  to complete");
    	  
    	   r2.wait();
      
    	   
       }catch(InterruptedException e){}
       System.out.println("Total is"+r1.x);
                  
        }
     	     
        }
     }
  }