@implSpec
This implementation returns a set that subclasses {@link AbstractSet}.
The subclass's iterator method returns a "wrapper object" over this
map's <tt>entrySet()</tt> iterator. The <tt>size</tt> method
delegates to this map's <tt>size</tt> method and the
<tt>contains</tt> method delegates to this map's
<tt>containsKey</tt> method.
<p>The set is created the first time this method is called,
and returned in response to all subsequent calls. No synchronization
is performed, so there is a slight chance that multiple calls to this
method will not all return the same set.
{@inheritDoc}
@implSpec This implementation returns a set that subclasses {@link AbstractSet}. The subclass's iterator method returns a "wrapper object" over this map's <tt>entrySet()</tt> iterator. The <tt>size</tt> method delegates to this map's <tt>size</tt> method and the <tt>contains</tt> method delegates to this map's <tt>containsKey</tt> method.
<p>The set is created the first time this method is called, and returned in response to all subsequent calls. No synchronization is performed, so there is a slight chance that multiple calls to this method will not all return the same set.