Returns the name of the default group for this class
For each class, the group "Default" is an alias for the group "<ClassName>", where <ClassName> is the non-namespaced name of the class. All constraints implicitly or explicitly assigned to group "Default" belong to both of these groups, unless the class defines a group sequence.
If a class defines a group sequence, validating the class in "Default" will validate the group sequence. The constraints assigned to "Default" can still be validated by validating the class in "<ClassName>".
string The name of the default group
public function getDefaultGroup() {
return $this->defaultGroup;
}