I am new to java and i have to make some changes to Tiny Java Web Server(LINK) and recompile it. Can someone please explain how it is done in java?
Usually i have been using javac command for compiling, but here i have multiple files to compile.
Also, i have read someone i should be using ant , but it seems complicated. Why does compiling a program have to be so complicated in java?
Can i compile it somehow using eclipse?
Answering your implied question "why can't all Java programs be compiled using Eclipse" -- you see, there are tools which compile Java programs consisting of many files (not just one), and these tools perform compilation automatically, without human operator, without using Eclipse (or any other IDE), so they need a compilation program. One such program is Ant, another popular in Java world is Maven.
Another point for Ant is that often you need just to compile program, not to edit it in anyway, so you don't need IDE, only compilation tool.
If you interested in understanding how these compilation tools work, I would suggest starting with Ant, then proceed to Maven (if needed).