class functions where the function name == class name

Hey there guys I just started trying out with writing classes. I've been looking at a lot of PEAR class files and noticed this: class classname { function classname() { } } I know that "$object = new classname;" will automatically run $object->classname();. But is it neccessary for every class to have this function? I read all these scripts and they all have them. I made one simple database class but it failed horribly, and I'm curious to if the initiated functions have anything to do with them. Thanks. Glenn