This was made with an old version of Java (pre 1.5) It uses enum as a variable name. Need to as (javac tells you) give command :
javac -source 1.4 gld/*.java
Note : when passing a path to Java both slashes work in Java
If your getting file not found your probably in the wrong folder.
Download a zip to a place lets say to folder:
D:\prog\j\
Now open command prompt, I assume you have java bin JDK in windows PATH?
So now you have default source download zip
gld_rel131_source.zip
in D:\prog\j\
Give following commands :
D:
cd D:\prog\j\
mkdir traffic2\src
cd traffic2\src
jar xf D:\prog\j\gld_rel131_source.zip
mkdir ..\bin
javac -d ../bin -source 1.4 gld/*.java
cd ..\bin
java gld.GLDSim