Detailed use synchronized to solve three threads in turn to print out 75 numbers

Original post see: http://www.iteye.com/topic/1117703

Problem Description:

A classic interview question about threading, requiring three threads to print 1,2,3,4,5 in order .... 71,72,73,74, 75.

Thread 1 Prints the 1,2,3,4,5 first, then the thread 2 prints the 6,7,8,9,10, then the thread 3 prints 11,12,13,14,15. Then the thread 1 prints 16,17,18,19,20 ... and so on until thread 3 prints to 75.

Directly on the code:

  Java code    package concurrent.test;        /**   *   Requirements Create three threads, output 1-75,   *  first thread output 1-5, second output 6-10, third output 11-15   *  then first thread output 16-20 ... Just go through the loop until you print out 75 numbers    *  @author  qiaoxueshi   *   */   public  class print1to75 {       static class printer implements  Runnable{           static int num =  1; //Start Digital            static final int  END = 75;           int id;                       Public printer (int id)  {                this.id = id;           }                      @ override           public void run () {               synchronized  (Printer.class)  {                    while (num <= end) {                        if (Num / 5 % 3 == id { //If it belongs to its own number, print out five                             system.out.print (id +  ":");   &NBsp;                        for (int i = 0; i < 5; i++) {                                 system.out.print (num++ +  ", ") );                            }                             System.out.println ();                                          &Nbsp;             printer.class.notifyall (); /Discard CPU usage, wake up the print threads waiting on the Print.class queue                         }else{                             try {                                printer.class.wait () ;//If not own number, hangs the current thread on the Printer.class object's waiting queue (also abandons the CPU right), waits for the wake-up                             }  catch  (interruptedexception e)  {                                 SYSTEM.OUT.PRINTLN ("id"  +  "interrupted");                            }                         }                    }               }            }       }                      public static void  main (String[] args)  {           //below can not press 0, 1,2 in the order, and in the middle of 22 casuallySleep (), will print correctly            new thread ( new  Printer (0)). Start ();           new thread ( new  printer (1)). Start ();           new thread (  New printer (2)). Start ();       }  }  

The comments are very clear, there are questions to welcome discussion.

Results (run n times, the results are consistent, please check):

Java code 0:1, 2, 3, 4, 5, 1:6, 7, 8, 9, 10, 2:11, 12, 13, 14, 15, 0:16, 17, 18, 19, 20, 1:21, 22, 23, 24, 25, 2:26, 27, 28, 29, 30,