Why can I anonymously subclass an enum but not a final class?

Question

This code:

public class Sandbox {
    public enum E {
        VALUE {
            @Override
            public String toString() {
                return \"I         


        

Answer 1

According to the JLS:

An enum type is implicitly final unless it contains at least one enum constant that has a class body.

In your example, VALUE has a class body and therefore E is not implicitly final.

Edit: Here's a quick example that validates the claim:

import java.lang.reflect.Modifier;

public class Sandbox {
  public enum E {
    VALUE {};
  }

  public enum E2 {
    VALUE;
  }

  public static void main(String[] args) {
    System.out.println(E.class);
    System.out.println(E.VALUE.getClass());
    System.out.println("E.VALUE is subclass of E = " + E.VALUE.getClass().getSuperclass().equals(E.class));
    System.out.println("E modifiers: " + Modifier.toString(E.class.getModifiers()));
    System.out.println("E2 modifiers: " + Modifier.toString(E2.class.getModifiers()));
  }
}

You can see from the output that the compiler is adding the final modifier to E2 but not to E:

class Sandbox$E
class Sandbox$E$1
E.VALUE is subclass of E = true
E modifiers: public static
E2 modifiers: public static final

Edit #2: Even though E is not final and is subclassed by VALUE, explicitly trying to extend it such as with class Foo extends E or enum Bar extends E is a compile-time error according to 8.1.4. Superclasses and Subclasses:

It is a compile-time error if the ClassType names the class Enum or any invocation of it.