same class in two jar files

[Prabhu Venkatachalam]

Say, you have a class like below,

package com.foo
public class a {}

jarfile1.jar and jarfile2.jar has above class.

Now you set a class path which has these JAR files. If you try to use class a in your code what will happen?

Thanks in advance.

[Jeroen T Wenting]

Why don't you try?

[Prabhu Venkatachalam]

Thanks Dude.

[Ilja Preuss]

Originally posted by Prabhu Venkatachalam:
Thanks Dude.

So what did you find out?

[Prabhu Venkatachalam]

I have not tried yet. If I got something, I'm sure I will share with ranchers.

Thanks.

[Ådne Brunborg]

I seem to recall having this problem as the cause for an "unexplainable bug" a couple of years back. Different version of class a was included in two different jar-files, and I kept getting the same old bug even though I knew I had included the new version.

The explanation was that the order in which the jar-files was included in the project determined which version of the class was used. This was using WebSphere Application Developer, and it preferred using the jar-file listed first of the two in the project library setup. Or possibly the last one.

[Ajith Kallambella]

This happens all the time, more often than you think. Just pick two jar files from your server class path and see how many classes they have in common.

A class loader will only load the class once, from the first "resource" it can find that has the class. So it is never a problem until as Ande points out, two different class loaders load potentially different versions of the class. When versions conflict, usually you get an error that hints that serialization identifier of the classfile is different than the one expected.