Why are functions getKey, getValue and setValue not associated with Map?
<p>As per Effective Java, Item 22, </p>

<blockquote>
  <p>Many Map implementations have an internal Entry object for each key-value pair in the map. 
  While each entry is associated with a map, the methods on an entry
  (getKey, getValue, and setValue) do not need access to the map.</p>
</blockquote>

<p>Can you explain what it means?  Can you give an example of a typical Map implementation to show how these functions aren't dependent on Map internals?</p>
