My Linux is Edubuntu 12.04 LTS. After downloaded & installing successfully "desktop4shared-1.3_1-all" package, 4shared doesn't work on my platform.
The 4shared package has a LOT of dependencies (additional packages required to run), including Java and other Java libraries. If you install the .deb with Software Center, all the dependencies should be automatically installed.
If not, or if your Ubuntu variant doesn't use Software Center, do this: