Presentation taken @ Kerala Java Users Group - Sep 30

1. Reflection - The most
important feature in
Java
Sarath Soman
@sarathsom4
sarathsoman.wordpress.com

2. About Me
Software Engineer @ Hifx

3. What is Reflection?
Reflection is the ability of a program to examine itself, modify its structure,
modify state using the structural information and generate new state and
structure.

4. How is reflection possible?
Representation of the source (metadata) should be available at runtime (The
compiler should bake the required meta information).
Runtime should provide APIs to reflect.

5. How does javac & jvm makes Reflection
possible?
Class file format
Class(.class) & the Class loader

6. Let’s see the bytecode of Contact.java

7. Let’s reflect on Contact.java

8. Why should I learn this?
Types of Programmers
Application Programmers - frameworks, libs, common design patterns
Library Designers - DSA, Design principles and patterns, API design
System Programmers - JVM, CLR, CPU, Native code programming, Cross
platform programming

9. Do you want to die as an average application
programmer ?

10. Let’s build a small Object Serialization lib

11. Limitations of Java Reflection
Cannot manipulate & generate code
Deep introspection on code is not possible
Solution : Need bytecode manipulation support.
Third party options : ASM, Javassist, BCEL, CGLIB

12. What is not covered
MethodHandles
Java 9 Changes

13. Few Articles
SimplifyJSPServlet - A web framework on top of Servlet, this makes use of
reflection
https://sarathsoman.wordpress.com/2014/05/29/making-simplifyjspservlet-thr
ead-safe/
PVSContainer - A dependency injection container, uses ASM to get class meta
data and reflection for dependency injection
https://sarathsoman.wordpress.com/category/java/pvscontainer/
Reflections in Golang -
https://sarathsoman.wordpress.com/2016/12/27/reflections-in-golang-example

14. Few Articles
The Class & The ClassLoader -
https://sarathsoman.wordpress.com/2014/01/15/the-class-the-classloader/
Java Reflection Example -
https://sarathsoman.wordpress.com/2014/01/12/invoking-methods-annotated-
with-the-time-for-invokation-using-java-reflection
Java Proxy -
https://sarathsoman.wordpress.com/2014/01/10/decoupling-cross-cutting-con
cerns-using-java-proxy-an-example

15. Github links
PVSContainer - https://github.com/nsarathsoman/PVSContainer
ObjectSerialization -
https://github.com/nsarathsoman/ObjectSerialization-KJUG-Demo
SimplifyJSPServlet - https://github.com/nsarathsoman/SimplifyJSPServlet
Proxy Demo - https://github.com/nsarathsoman/KJUG-Demo-Sep-Proxy

16. Slang Compiler
https://github.com/nsarathsoman/SlangCompiler
https://github.com/nsarathsoman/slang4JVM
A higher order function in Slang
function (int,int)->int adder()
var z = 10;
var x = lambda int (int x, int y)
println x;
println y;
return ( x + y ) * z;
endlambda
return x;
end

17. Thank You