serialVersionUID is used for Serializable classes. I don't know about MyEclipse, but in the standard Eclipse, clicking on the icon which shows the warning will display a popup menu, with "Create serialVersionUID". Selecting this will add a serialVersionUID for you.
if you don't care about serialization, you can still add the default ID in your class : [code] private static final long serialVersionUID = 1L; [code] [ February 21, 2007: Message edited by: Satou kurinosuke ]
You can turn that eclipse warning off in Window-Preferences->Java->Compiler->Errors/Warnings->Potential programming problems.
About Serial UID: serialVersionUID is used to ensure that someone using a newer version of your class can't deserialize an older instance or vice versa. Typically, if you change something minor in your class, like the implementation of a method, a old, saved instance of your class could be used with the new version without any problems. If you change the names of the class' fields or alter the purpose of the class, though, instances of that class that were saved under a previous version probably won't play well with the new class version. If you change something minor in your class, you can leave the serialVersionUID alone, but if you change something major, it's a good idea to change the serial version so that you or others don't get weird errors when using old instances with the new class.