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I am studying Java and wrote a very simple program. In it I can put enums in the top most level, but not inside a method. The way I see it, enums are almost like constants, so why not use them inside methods?
In my program, enum1 is allowed, but enum2 is not. Why?
enum enum1 {A, B, C};
public static void main(String[] args)
{
enum enum2 {A, B, C}; // only on a top level class or interface
}
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You can't have a static nested type inside a non-static one (a.k.a an "inner class", see JLS §8.1. 3. Inner Classes and Enclosing Instances). Therefore you can't have an enum inner type inside a non-static nested type.
Interfaces are designed to define common behaviours, enums to define common values. Enum represents a real value which can be compared to another value, or stored in the database easily.
Yes, we can define an enumeration inside a class. You can retrieve the values in an enumeration using the values() method.
Yes, Enum implements an interface in Java, it can be useful when we need to implement some business logic that is tightly coupled with a discriminatory property of a given object or class. An Enum is a special datatype which is added in Java 1.5 version.
This small article provides an outline of the usage of classes and enums inside an interface that seem to be unusual to a developer. I recently was interviewing for candidates and I asked the basic question of whether we can declare enums and classes inside an interface. Most candidates said "NO" but the answer is "Yes" .
An enum is a special "class" that represents a group of constants (unchangeable/read-only variables). To create an enum, use the enum keyword (instead of class or interface), and separate the enum items with a comma: Enum is short for "enumerations", which means "specifically listed".
Because enums are a special type of class definition. This doc describes some information about special things the compiler does including adding static methods (valueOf). While you could declare an anonymous class withing the context of a method, it could not have static methods.
C++11 has introduced enum classes (also called scoped enumerations ), that makes enumerations both strongly typed and strongly scoped. Class enum doesn’t allow implicit conversion to int, and also doesn’t compare enumerators from different enumerations. To define enum class we use class keyword after enum keyword.
Because enums are a special type of class definition.
This doc describes some information about special things the compiler does including adding static methods (valueOf). While you could declare an anonymous class withing the context of a method, it could not have static methods.
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It may have to do with the fact that Enums are compiled similarly to classes. For the same reason you cannot declare a class definition inside a method, you cannot declare in enum either.
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