Building code at runtime.

Question

Hello,
I am wondering if this is even possible ... Imagine having a class written as follows:public class HelloWorld{
   public sayHello(){
      // This space was left on purpose.
}Now I have a text file (example sayHello.txt) with the following text in it.System.out.println(�Hello, World!�);Is it possible to load the text file text and make it get executed when I call the sayHello Method?
I mean it is like building some code at runtime.
Thanks and Regards,
Sim085

Answer 1

The JVM itself only handles the bytecode. It doesn't even need .class-files, the classloader just passes it a byte[] and tells it to parse that as a class definition. Where that byte[] comes from doesn't matter. Most of the times it's read from a class file in the file-system, a jar or a URL, but it can just as well be runtime-generated by some scripting language.
The other alternative of course is to write a scripting language interpreter in Java that happens to be able to call java methods. The effect is pretty much the same, except you don't have to care about class loader issues and it might be a tad slower.
I don't exactly know which of these two categories Groovy, Jython and BeanShell fit into.