question: public static < E extends Enum < E > > EnumSet < E > of ( E e1 , E e2 , E e3 ) { EnumSet < E > set = of ( e1 , e2 ) ; set . add ( e3 ) ; return set ; }
target:  Creates a new enum set, containing only the specified elements. There are six overloadings of the method. They accept from one to five elements respectively. The sixth one receives an arbitrary number of elements, and runs slower than those that only receive a fixed number of elements.