gistfile1.java

public class SynchronizedCounter {
    private int c = 0;

    public synchronized void increment() {
        c++;
    }

    public synchronized void decrement() {
        c--;
    }

    public synchronized int value() {
        return c;
    }
}

public void updateWordCount(HashMap<String, SynchronizedCounter> counts, String wordToUpdate){
    if (counts.containsKey(wordToUpdate)) {
        SynchronizedCounter current_count = counts.get(wordToUpdate);
        current_count.increment();
    } else { //still vulnerable here to race conditions. just pay attention to above
        SynchronizedCounter new_count = new SynchronizedCounter();
        new_count.increment();
        counts.put(wordToUpdate, new_count);
    }
}