Understanding the Java Virtual Machine: Class Loading and Reflection
by Kevin Jones
This course covers some of the fundamentals and inner workings of the Java Virtual Machine. This class will be the first in the series and will examine class loading.
What you'll learn
Java is built around classes; these classes have to be loaded into memory and loading that is the responsibility of class loaders. The first part of this course will look at this class loading mechanism and how to write class loaders. Once you understand this, several scenarios become available, such as hot deployment of classes and the side-by-side loading of classes. Java has a rich type system and rich metadata. Reflection is the mechanism by which you can examine that metadata at runtime, and use that information to build rich applications. In the second part of this course, we will see how to use reflection to both examine this metadata at runtime and use it within our applications.
About the author
A long time ago in a university far, far away Kevin fell in love with programming. Initially on the university's DEC20 computer doing BASIC and Pascal and a little bit of Fortran. His first job had him writing batch PL/1 on an IBM mainframe where he also discovered the arcane delights of JCL. He soon realized the multiuser systems were not for him after discovering the delights of dBase IV on IBM PCs. From here it was all downhill as he became addicted to C and the Windows API. Just missing out ... moreon coding for Windows 1, he did code for the other 16 bit versions of Windows, 2 and 3, including the various network-ready versions. He still remembers the awkwardness of having to carry an IBM Token Ring MAU with him wherever he went.
After trying to pretend that Windows and C were really object oriented he decided that it would be better to learn C++. It was around this point that he realized that as well as writing code for a living he could be paid for telling people how to write code for a living. He taught Windows, MFC and C++ for a UK training company before his spirit was broken on the back of the OLE support in MFC when he finally stepped away from the nightmare of unmanaged code to the nirvana of the managed runtime called Java.
It was at this time that he spoke at several JavaOne conferences usually on the subject of Servlets, JavaServer Pages and tag libraries. After buying the Sun employees copious amounts of Apple Martini Kevin was invited onto the expert groups for the Servlet and JSP specifications.
Oh, how he laughed when .Net appeared and the same arguments raged about non-deterministic destruction and garbage collection that were now so old hat in the Java world. He finally got his hands dirty in C# and .Net about eight years ago, again working in the web tier and hating every minute of the using the monstrosity that was and is ASP.Net Web Forms. It wasn't until MVC appeared that he finally felt he had come home to Microsoft.
Now of course MVC is so last year and Kevin is focusing more and more on rich clients using JavaScript and tools such as Knockout and AngularJS. He believes that JavaScript is the best thing since, well, JavaScript.
He still retains his passion for developing and teaching; spending about a quarter of the year doing the latter and most of the time doing the former.
When not stuck in front of a computer you can find him: with his nose in a book, a good one preferably, but almost any book would do; watching a film; walking; running; or annoying his wife by watching sports on television.
