Can you configure Windows to open JAR files like ZIP files without a 3rd party tool?

Question

Can someone please let me know why is the below code not threadsafe ? The output I get is either 0 or 45 or 90. The shared resource counter has a synchronized method, so I am expecting 90 as the output all the times. Am I missing something here ? Please advise. Kindly, also let me know how to make this code threadsafe.

class Counter{

    long count = 0;

    public synchronized void add(long value){
      this.count += value;
    }
 }
 class CounterThread extends Thread{

    protected Counter counter = null;

    public CounterThread(Counter counter){
       this.counter = counter;
    }

    public void run() {
    for(int i=0; i<10; i++){
          counter.add(i);
       }
    }
 }
 public class Example {

   public static void main(String[] args){

     Counter counter = new Counter();
     Thread  threadA = new CounterThread(counter);
     Thread  threadB = new CounterThread(counter);

     threadA.start();
     threadB.start();

     System.out.println(counter.count);
   }
 }

Solution 1

I tried exporting HKEY_CLASSES_ROOT\.zip, changing all references of '.zip' to '.jar' and importing it to HKEY_CLASSES_ROOT\.jar.

Under Vista at least it let me open a .jar file as if it were a .zip.

Solution 2

What you need to do is associate the JAR extension in Windows Explorer with Compressed folders. From Windows Explorer select tools / Folder Options. Then the Files Types tab. Select New and associate JAR Compressed (ZIP) Folder.

Comments

[Eugen Martynov]

Read about visibility jeremymanson.blogspot.nl/2007/08/…. Maybe I'm wrong

[JohnB]

@Eugen: Hm, probably you are right. Making count volatile should help as well (with visibility, not with the original question), shouldn't it?

[user1445850]

I tried making the variable volatile, it does not work. The output again can be 0 or 45 or 90. Thread.join seems to be a perfect solution.

[user1445850]

I tried sleeping the main thread & I got the output as 90. The fact that there are 3 threads here, was causing the confusion.

[JohnB]

Volatile, of course, does not solve your issue. You should, however, make count volatile in addition, for the reason pointed out by Eugen.