Is this valid Java code?
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开发者_如何转开发 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...
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);
}
Seems reasonable...
What if you take the "implements MessageType" off of your class, does it still crash?
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?
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.
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