HelloWorld Example Won't compile

[Charles Curley]

I took the source for the HelloWorld example in the Tomcat5 samples
(http://your.server:8080/servlets-examples/helloworld.html), and tried
to compile it.

[javac] Compiling 1 source file to /home/ccurley/src/com/charlescurley/hello/classes
    [javac] ----------
    [javac] 1. WARNING in /home/ccurley/src/com/charlescurley/hello/src/HelloWorld.java
    [javac]  (at line 5)
    [javac]     public class HelloWorld extends HttpServlet {
    [javac]                  ^^^^^^^^^^
    [javac] The serializable class HelloWorld does not declare a static final serialVersionUID field of type long
    [javac] ----------
    [javac] 1 problem (1 warning)

What am I missing here?

[ccurley@taltos src]$ echo $CLASSPATH
/usr/share/tomcat5/bin/:/usr/bin:/usr/share/java/servletapi5.jar:.

[Andrew Overholt]

* Charles Curley  [2005-08-23 22:20]:
> [javac] ----------
> [javac] 1. WARNING in /home/ccurley/src/com/charlescurley/hello/src/HelloWorld.java
>
> [...]
>     [javac] The serializable class HelloWorld does not declare a static final serialVersionUID field of type long
>     [javac] ----------
>     [javac] 1 problem (1 warning)
>
> What am I missing here?

Isn't that just a warning and not an error?  ecj is a little more
particular than other bytecode compilers WRT serialVersionUIDs IIRC.

Andrew

[Charles Curley]

On Tue, Aug 23, 2005 at 11:16:21PM -0400, Andrew Overholt wrote:
> Charles Curley  [2005-08-23 22:20]:
> > [javac] ----------
> > [javac] 1. WARNING in /home/ccurley/src/com/charlescurley/hello/src/HelloWorld.java
> >
> > [...]
> >     [javac] The serializable class HelloWorld does not declare a static final serialVersionUID field of type long
> >     [javac] ----------
> >     [javac] 1 problem (1 warning)
> >
> > What am I missing here?
>
> Isn't that just a warning and not an error?  ecj is a little more
> particular than other bytecode compilers WRT serialVersionUIDs IIRC.
>
> Andrew

I guess I'm a little picky about warnings. I learned way back when
ANSI C was all the latest rage that ignoring them was not a good
idea.

Anyway, turns out the solution is to declare the dang thing:

public class HelloWorld extends HttpServlet {
    static final long serialVersionUID = 0;

Now a C compiler (or lint) would have complained that it isn't
used. Sigh.

Thanks

[Tom Tromey]

> > > > > "Charles" == Charles Curley  writes:

Charles> public class HelloWorld extends HttpServlet {
Charles> 	static final long serialVersionUID = 0;

Charles> Now a C compiler (or lint) would have complained that it isn't
Charles> used. Sigh.

java compilers should know to special case serialVersionUID.
It is customary to make this private.

Tom