I'm pretty confused about the whole process of setting up external build tools for Eclipse. I found this FAQ item but I'm not sure how the example given would apply to what I want to do.

The file I will be editing is a XML file with a .kflex extension. It is the input for a program called KFlex. KFlex generates a number of Java source files, along with another text file which is the input for a program called JFlex. JFlex generates additional Java sources. Finally, I want all the Java source to be built.

If it makes a difference, KFlex and JFlex are both Java programs themselves. I'm wondering if there's a way to make builds more efficient by running them in Eclipse's JVM instead of starting another JVM.