AHHP AHHP - 2 months ago 15
Java Question

Static enum vs. Non-static enum

What's the difference between static and non-static enum in Java? Both usages are same.

Is it correct that all static ones are loaded on memory on startup, and non-static ones are loaded on demand?
If yes, then which method is better? Keeping some data always in memory or using server resources to load them each time?

public class Test {

public enum Enum1 {
A, B
}

public static enum Enum2 {
C, D
}

public static void main(String[] args) {
Enum1 a = Enum1.A;
Enum1 b = Enum1.B;

Enum2 c = Enum2.C;
Enum2 d = Enum2.D;
}
}

Answer

All enums are effectively static. If you have a nested enum, it is much the same as a static class.

All classes are lazily loaded (enums or otherwise) however when they are loaded they are loaded all at once. i.e. you can't have a few constants loaded but not others (except in the middle of class initialization)

Java allows certain modifiers to be implicit to avoid having to declare them all the time. This means that adding a modifier doesn't always do anything other be a longer way of writing the same thing.

Default modifiers for

class field/method/nested class - package local, non-final, non-static

enum and nested enum - package local, final and static

interface field - public static final

interface method - public abstract

nested class in an interface - public static, non-final

Note: while static is optional for an enum it is always static. However, final cannot be set for an enum even though it is always notionally final (Technically you can have subclasses with overridden implementations for constants)

EDIT: The only place you need to use static with enum is with import static of an enum's value. Thank you @man910

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