Is this valid Java code?

Question

I'm using Eclipse, and it is perfectly happy with the following code:

public interface MessageType
{
    public static final byte   KICK     = 0x01;
    public static final byte   US_PING  = 0x02;
    public static final byte   GOAL_POS = 0x04;
    public static final byte   SHUTDOWN = 0x08;
    public static final byte[] MESSAGES = new byte[] {
        KICK,
        US_PING,
        GOAL_POS,
        SHUTDOWN
    };
}

public class MessageTest implements MessageType
{
    public static void main(String[] args)
    {
        int b = MessageType.MESSAGES.length;    //Not happy
    }
}

However, the platform that I'm running it on crashes at the line marked above. By crash, think an equivalent of a BSOD. Is there anything wrong with my code, or do I need to pursue the developers of the Java VM for my platform?

---

EDIT:

Ok, thanks for your responses. It turned out to be a bug in the Java VM. To quote the developer, 'gloomyandy',

This is a known problem with interfaces that have a static initializer. It is fixed in the current development builds...

Answer 1

I don't see any problem with this code, other than that if you are using Java5 or above, you would be better off using an enum:

public enum MessageType
{
    KICK     (0x01),
    US_PING  (0x02),
    GOAL_POS (0x04),
    SHUTDOWN (0x08);

    private byte value;
    MessageType(byte value) { this.value = value; }
    byte getValue() { return value; }
}

public class MessageTest
{
    public static void main(String[] args)
    {
        int b = MessageType.values().length;    //Should be happy :-)
    }
}

Update: to recreate the enum value from its byte representation, you need to supplement MessageType with the following (adapted from Effective Java, 2nd Ed. Item 31):

private static final Map<Byte, MessageType> byteToEnum = new HashMap<Byte, MessageType>();

static { // Initialize map from byte value to enum constant
  for (MessageType type : values())
    byteToEnum.put(type.getValue(), type);
}

// Returns MessageType for byte, or null if byte is invalid
public static MessageType fromByte(Byte byteValue) {
  return byteToEnum.get(byteValue);
}

Answer 2

Seems reasonable...

What if you take the "implements MessageType" off of your class, does it still crash?

Answer 3

The code itself is perfectly sound. I can compile and run it perfectly fine on my Win7 machine (with Java6); it sounds like you're using some unusual system?

Answer 4

As everybody told, it should work.
You can try this one:

public class MessageTest implements MessageType
{
    public static void main(String[] args)
    {
        int b = MESSAGES.length;    // no MessageType here
    }
}

(MessageType is not needed since the class is implementing it).
I still would prefer the way Péter Török suggested.