The following enum when it was compiled it will generate a class file.
The class file was executable with java.
Which does n't look good,
it starts executing and comes out with no main method exception.

The following are the code and console for verification.
vishalb:/home/vv145429/tiger/bugs/jan302k+4 82 % javac -source 1.5 Suit.java
vishalb:/home/vv145429/tiger/bugs/jan302k+4 83 % java Suit
no thing
no thing
thing = red
thing = black
Exception in thread "main" java.lang.NoSuchMethodError: main
vishalb:/home/vv145429/tiger/bugs/jan302k+4 84 % cat Suit.java
public enum Suit {
    clubs, diamonds,
    hearts("red") {
        public boolean comingUpDiamonds() { return true; }
    }
    ,
    spades("black");
    

    // constructors
    private Suit(String thing) {
        System.out.println("thing = " + thing);
    }
    private Suit() {
        System.out.println("no thing");
    }

    public boolean comingUpDiamonds() {
        return false;
    }
}

vishalb:/home/vv145429/tiger/bugs/jan302k+4 85 %