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:.

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[Andrew Overholt]

* Charles Curley <charlescurley(a)charlescurley.com&gt; [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 <charlescurley(a)charlescurley.com&gt; [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


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[Tom Tromey]

> >>>> "Charles" == Charles Curley
> <charlescurley(a)charlescurley.com&gt; 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