Returns true if this PermissionCollection object is marked as readonly.
If it is readonly, no new Permission objects can be added to it
using {@code add}.
<p>By default, the object is <i>not</i> readonly. It can be set to
readonly by a call to {@code setReadOnly}.
@return true if this PermissionCollection object is marked as readonly,
false otherwise.
Returns true if this PermissionCollection object is marked as readonly. If it is readonly, no new Permission objects can be added to it using {@code add}.
<p>By default, the object is <i>not</i> readonly. It can be set to readonly by a call to {@code setReadOnly}.
@return true if this PermissionCollection object is marked as readonly, false otherwise.