Q:

Unable to use existing Java packages in Eclipse?

I'm learning Java from Bruce Eckel's Thinking in Java. After reading about packages early through the book, I thought I had got it, but when I decided to use the supplementary code(in the form of a single ZIP), I'm not so sure anymore. 
The ZIP file contains packages in the correct hierarchy. I've an extracted copy of the ZIP too. Let's call this folder TIJ4. Both the ZIP and the folder are located on my Desktop. I'm working with an example Shapes.java which has an import statement like this: 
import polymorphism.shape.*;. I imported this folder in the Project Properties>Libraries>Add external class folder. The strange thing is that Eclipse does not show an error on the import line, yet it cannot resolve names to types. I could manually create a package, then a class from within Eclipse, but isn't there an easier way to do this?
I've gooogled about this but nobody seems to have the exact problem as me. Here's what I've got so far:
1)New Java Project created. Created a class file Shapes.java in the project:

2) Project Properties>Libraries>Add External Class Folder. Selected my folder TIJ4. Notice that the error on the import is now gone. Apparently Eclipse has found the polymorphism package.

3)But I still get XXX cannot be resolved to a type errors all over the place!
what do I do? I also tried Project>Build Path>Add external archives and selected the ZIP, however, ended up in the same place. 

A:

As the Zip file contains only Java sources, you will have to compile them. Simple way, right now, is extract them into the src directory in your eclipse project. That way they will be compiled and automatically included in the classpath.
The reason for not able to resolve the classes even the import error goes away, is the zip file contains the directories that satisfy the package structure but there are no compiled classes (the .class files) are found in them.

