Decompiled enum – behind the scenes

Every user-defined enum implicitly extends the java.lang.Enum class. Behind the scenes, the one-line Size enum (defined in the preceding section) is compiled into something similar to the following (I've added comments in the code to explain it; when you compile an enum, you won't get similar comments):

final class Size extends Enum                 // 'enum' converted to final class  
{ 
    public static final Size SMALL;           // variables to store  
    public static final Size MEDIUM;          // enum constants 
    public static final Size LARGE;           //  
 
    private static final Size $VALUES[];    // array of all enum 
                                            // constants 
 
    static 
    {                                       // static initializer 
        SMALL = new Size("SMALL", 0);       // to initialize enum                                                                                             
                                            // constants 
        MEDIUM = new Size("MEDIUM", 1);     // 
        LARGE = new Size("LARGE", 2);       // 
        $VALUES = (new Size[] {             // 
            SMALL, MEDIUM, LARGE            // & populate array of enum                                             
                                            // constants 
        }); 
    } 
    public static Size[] values() 
    { 
                return (Size[])$VALUES.clone();       // Avoiding any                                                                                                          
                                                    // modification to  
    }                                // $VALUES by calling methods 
    public static Size valueOf(String s) 
    { 
        return (Size)Enum.valueOf(Size, s); 
    } 
    private Size(String s, int i) 
    { 
        super(s, i); 
    } 
} 

Enums are syntactic sugar. The compiler takes your enum construct and extends java.lang.Enum to create a class. It adds the variables, initializers, and methods to get the required behavior.