src/main/java/com/workplacesystems/utilsj/collections/TransactionalHashMap.java
@Override
    public V put(K key, V value) throws ConcurrentModificationException
    {
        K k = maskNull(key);
        int hash = hash(k);
        int i = indexFor(hash, table.length);
        
        V oldValue = null;
        for (Entry<K,V> e = table[i]; e != null; e = e.next)
        {
            if (e.hash == hash && eq(k, e.key))
            {
                //check if someone else has a pending add for the same key
                if (e.is(Entry.ADDED, null) && !e.is(Entry.ADDED, getCurrentThreadId()))
                    throw new ConcurrentModificationException();
                
                if (validEntry(e))
                {
                    oldValue = e.value;
                    //if not transactional can reuse entries
                    if (auto_commit)
                    {
                        e.value = value;
                        return oldValue;
                    }
                    else
                        e.setStatus(Entry.DELETED, getCurrentThreadId());
                }
            }
        }
        
        modCount++;
        addEntry(hash, k, value, i);
        return oldValue;
    }
@Override
    public V put(K key, V value) throws ConcurrentModificationException
    {
        K k = maskNull(key);
        int hash = hash(k);
        int i = indexFor(hash, table.length);
        
        V oldValue = null;
        for (Entry<K,V> e = table[i]; e != null; e = e.next)
        {
            if (e.hash == hash && eq(k, e.key))
            {
                //check if someone else has a pending add for the same key
                if (e.is(Entry.ADDED, null) && !e.is(Entry.ADDED, getCurrentThreadId()))
                    throw new ConcurrentModificationException();
                
                if (validEntry(e))
                {
                    oldValue = e.value;
                    //if not transactional can reuse entries
                    if (auto_commit)
                    {
                        e.value = value;
                        return oldValue;
                    }
                    else
                        e.setStatus(Entry.DELETED, getCurrentThreadId());
                }
            }
        }
        
        modCount++;
        addEntry(hash, k, value, i);
        return oldValue;
    }
Associates the specified value with the specified key in this map.
If the map previously contained a mapping for this key, the old
value is replaced.

@param key key with which the specified value is to be associated.
@param value value to be associated with the specified key.
@return previous value associated with specified key, or <tt>null</tt>
if there was no mapping for key.  A <tt>null</tt> return can
also indicate that the HashMap previously associated
<tt>null</tt> with the specified key.