value
通过原始值获取操作类型。
Return
已知操作类型；未知值返回 null。
Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)
Return
the enum constant with the specified name
Throws
Illegal
if this enum type has no constant with the specified name