![]() Java enums are tightly immutable, so it makes sense that the enum must return a clone of the array returned by the values() method each time that method is called to ensure that the array associated with the enum is not changed.Ī recent post on the OpenJDK compiler-dev mailing list titled " about Enum.values() memory allocation" observes that " Enum.values() allocates a significant amount of memory when called in a tight loop as it clones the constant values array." The poster of that message adds that this "is probably for immutability" and states, "I can understand that." This message also references a March 2012 message and associated thread on this same mailing list. The problem, however, is that Enum.values() returns an array and arrays in Java are mutable. ![]() Example 8.9.3-1 ("Iterating Over Enum Constants With An Enhanced for Loop") demonstrates calling Enum.values() to iterate over an enum. Section 8.9.3 ("Enum Members") lists two " implicitly declared methods": public static E values() and public static E valueOf(String name). In The Java Language Specification Java SE 10 Edition, it is Section 8.9 that covers enums. ![]() The Java Language Specification spells out enum behavior. In particular, the Java enum's method values() returns a new copy of an array representing its possible values each and every time it is called. It seemed like we waited forever to get it, but when we did finally get it ( J2SE 5), the enum was so much better than that provided by C and C++ that it seemed to me " well worth the wait." As good as the Java enum is, it's not without issues. Month name, Planet names etc as these entities will have fixed set of known values.I'm a big fan of Java's enum. For example you can use enum for declaring Days name, You should use that entity as an enum type. Of an entity at compile time(or design time) and you know that these values won't change later, If you know all possible values(constant) You should use enum types any time you need to represent a fixed set of constants. No such specific methods are added with classes.Įach enum-type internally extends Enum class. Java compiler adds some methods like values(), valueOf() to an enum type after compilation. Enum program with method, constructor and variableĮnums are generally used to declared a set of pre-defined constants.Ĭlasses are design to expose state and behavior of an object.Ĭonstructor of an enum type can be private or package-private only.Ī class constructor can have any access modifier.įirst line of code must be constant declaration.Ĭlasses doesn't have any such restrictions. The program below shows the usage of method, constructor and variable inside an enum type. Since each constant in an enum type is internally an instance of enum type, so we can call the methods of an enum type by using it'sĬonstants. The access modifier of constructor for an enum type must be either private or package-private(no modifier).Īn enum type can have multiple constructors. Looks for the matching constructor while compilation. If the enum type contains constructor, ensure that you have a matching constructor for each constant declaration since it The enum constant declaration must end with semicolon( ) if the enum type contains method, constructor or field. The first line of code in an enum type must be constant declaration. ![]() ➤ Overriding using Covariant Return TypeĬurrent direction = NORTH Variable, Method and Constructor in EnumĪn enum type can have methods, constructors and variables as well, but they must be declared after constant declaration.➤ Overloading and Overriding Differences.➤ Runtime and Compile-time Polymorphism.➤ Overflow Underflow Widening Narrowing.
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