An object that has no correlation between its state and its hash code value should typically not be used as the key. For example, String objects are better than StringBuilder objects for use as keys.
You can also use the Item property to add new elements by setting the value of a key that does not exist in the DictionaryBase; for example, myCollection["myNonexistentKey"] = myValue. However, if the specified key already exists in the DictionaryBase, setting the Item property overwrites the old value. In contrast, the Add method does not modify existing elements.