Java Multi-threading : Unexpected result

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I am working on a Enterprise application. I am facing some issues while running application in multithreaded environment. I am writing a program in which there is a variable whose value is getting updated(incremented) at very fast rate (for example 10000 updates/persecond). A loop runs for certain iterations and the value of the variable is incremented and stored in HashMap. Once the loop terminates and value the variable in HashMap is printed. I am getting unexpected value of the variable.

Here is demo program (Please read comments for better understanding) :

class test implements Runnable {

    static ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
    static AtomicInteger value_to_be_incremented_stored = new AtomicInteger(0); // variable whose value to be updated
    static AtomicInteger i = new AtomicInteger(0);  // this runs the loop

    @Override
    public void run() {

        for (i.set(0); i.get() < 100000; i.incrementAndGet()) {
            /*
                This loop should run 100000 times and when loop terminates according to me value of variable 
                "value_to_be_incremented_stored" should be 100000 as its value is incremented 
                100000 times the loop also runs 100000 times. 
            */
            System.out.println("Thread > " + Thread.currentThread() + "  " + value_to_be_incremented_stored.incrementAndGet());
            map.put("TC", value_to_be_incremented_stored.intValue());
        }

        System.out.println("Output by Thread  " + Thread.currentThread() + "     " + map.toString());
    }

    public static void main(String[] args) {

        test t1 = new test();
        Thread thread1 = new Thread(t1);
        thread1.setName("Thread 1");

        Thread thread2 = new Thread(t1);
        thread2.setName("Thread 2");

        Thread thread3 = new Thread(t1);
        thread3.setName("Thread 3");

        Thread thread4 = new Thread(t1);
        thread4.setName("Thread 4");

        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();

    }
}

Output (it varies) :

My output

Issue : I am running loop for 100000 times (i.get() < 100000) then how come value of variable value_to_be_incremented_stored becomes more than 100000.

3 Answers
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