Christopher Hinds wrote:
>
> This may sound like a stupid question but aside from the obvoius technical
>
> reason(s), can someone please give a real-world example where this could
> be used ( ie.. calling a instanance method(s) in the constructor of the
> superclass before
> the superclass has been completely constructed)?
The actual code that provoked me to find this
bug goes something like this below. The problem
is with the `user' variable, since `receiveBody'
is called before this variable has been constructed.
I've since been able to rework the code (using
a static method in the Message* subclasses to
act as a factory for those message types) and
it works better now.
Rich.
/* Message.java */
public abstract class Message
{
protected Message (DataInputStream input, int type)
throws MessageProtocolError, IOException
{
int streamType = input.readInt ();
if (streamType != type)
throw new MessageProtocolError ("incorrect message type " +
streamType +
" (expecting " +
type +
")");
receiveBody (input);
}
protected abstract void receiveBody (DataInputStream input)
throws IOException, MessageProtocolError;
}
/* Lots of Message* classes implementing particular
* message types, of which one looks like this:
*/
public class MessageUserLogin extends Message
{
public String user /* = null */;
private static final int type = MessageType.UserLoginType;
/**
* Construct message from input stream of known type.
*/
public MessageUserLogin (DataInputStream input)
throws MessageProtocolError, IOException
{
super (input, type);
}
/**
* Receive the message.
*/
protected void receiveBody (DataInputStream input)
throws IOException
{
this.user = input.readUTF ();
}
}
--
- Richard Jones. Linux contractor London and SE areas. -
- Very boring homepage at: http://www.annexia.demon.co.uk/ -
- You are currently the 1,991,243,100th visitor to this signature. -
- Original message content Copyright (C) 1998 Richard Jones. -
