java - Multithread programming and incrementing a static variable -

i have read posts related problem not solve problem. code question in big java - object of cay horstmann. question asks counting word of several files using multithread programming , store combined words counting problem.

in order combined counter used static variable incremented on each of iteration of counting words in threads. used reentrantlock() make incrementing available 1 thread @ time. works fine except incrementing. seems static variable not incremented. tested number of lock() , unlock() each thread , match expected result static variable not work properly.

is there explanation it? thank time , help.

my task class:

 import java.io.file;  import java.io.filenotfoundexception;  import java.util.scanner;  import java.util.concurrent.locks.lock;  import java.util.concurrent.locks.reentrantlock;  public class wordcount implements runnable {     private string filename;     scanner inputfile;     private long counter;     public volatile static long combinedcounter = 0;     lock cclock;      public wordcount(string aname) throws filenotfoundexception     {         try         {             this.cclock = new reentrantlock();             this.counter = 0;             this.filename = aname;             this.inputfile = new scanner(new file(this.filename));         }         catch (filenotfoundexception e)         {}      }     public void ccount()     {         cclock.lock();         try         {             combinedcounter++;             /*synchronized (this)             {                 combinedcounter++;             }*/          }                 {             cclock.unlock();         }      }     @override     public void run()     {         try         {             while (inputfile.hasnext() && !thread.interrupted())             {                  synchronized (this)                  {                      ccount();                  }                  counter++;                  inputfile.next();                  thread.sleep(0);              }              system.out.printf("%s: %d\t\t%d\n", this.filename,                         this.counter,combinedcounter);         }          catch (interruptedexception e)          {}      }  } 

this client class:

    import java.io.filenotfoundexception;     import java.util.concurrent.executorservice;     import java.util.concurrent.executors;      public class wordcountrunner     {          public static void main(string[] args) throws filenotfoundexception,                 interruptedexception         {             string = "a.txt";             string b = "b.txt";             executorservice pool = executors.newfixedthreadpool(2);             ;             try             {                 runnable r1 = new wordcount(a);                 runnable r2 = new wordcount(b);                 pool.execute(r1);                 pool.execute(r2);                  while (!pool.isterminated())                 {                     pool.shutdown();                 }                 thread.sleep(100);                 system.out.print("***" + wordcount.combinedcounter);             }             catch (filenotfoundexception e)             {              }                         {                 pool.shutdown();              }         }      } 

the lock not work because reentrantlock instance variable in wordcount class. so, each instance of class has own private lock , don't synchronize each other. easiest change make lock static, variable it's protecting.