multithreading example with synchronization

here is the same example which prints counter value in sequence and every time we run it, it produces the same result.

example

class printdemo {
   
   public void printcount() {
      
      try {
         
         for(int i = 5; i > 0; i--) {
            system.out.println("counter   ---   "  + i );
         }
      } catch (exception e) {
         system.out.println("thread  interrupted.");
      }
   }
}

class threaddemo extends thread {
   private thread t;
   private string threadname;
   printdemo  pd;

   threaddemo(string name,  printdemo pd) {
      threadname = name;
      pd = pd;
   }
   
   public void run() {
      
      synchronized(pd) {
         pd.printcount();
      }
      system.out.println("thread " +  threadname + " exiting.");
   }

   public void start () {
      system.out.println("starting " +  threadname );
      
      if (t == null) {
         t = new thread (this, threadname);
         t.start ();
      }
   }
}

public class testthread {

   public static void main(string args[]) {
      printdemo pd = new printdemo();

      threaddemo t1 = new threaddemo("thread - 1 ", pd);
      threaddemo t2 = new threaddemo("thread - 2 ", pd);

      t1.start();
      t2.start();

      // wait for threads to end
      try {
         t1.join();
         t2.join();
      } catch (exception e) {
         system.out.println("interrupted");
      }
   }
}

this produces the same result every time you run this program −

output

starting thread - 1
starting thread - 2
counter   ---   5
counter   ---   4
counter   ---   3
counter   ---   2
counter   ---   1
thread thread - 1  exiting.
counter   ---   5
counter   ---   4
counter   ---   3
counter   ---   2
counter   ---   1
thread thread - 2  exiting.