Yes, you can remove older versions of Java and keep just the latest version that is installed on your system and yes, this will free disk space.
A very small number of Java applications may require specific versions of Java in order to run. However this is quite rare and most people are running few or no Java applications to begin with. If you discover you truly must have a particular old version of Java you can obtain it from Sun's archive pages. But most users can simply uninstall old versions of Java.
Windows users can uninstall old versions of Java by following these steps:
1. Click "Start"
2. Select "Control Panel"
3. Double-click "Add/Remove Programs"
4. Select the oldest version of Java on your system and remove it
5. Repeat this process as needed, but do not delete your newest version of Java.
If you should accidentally delete all versions of Java from your system, you will lose the ability to completely view a small number of web pages which contain Java "applets" (similar to Flash, but a different technology from Sun). You will also lose the ability to run Java "applications." There are a few popular Java applications around, notably including various BitTorrent clients and similar software.
Fortunately, you can easily reinstall Java by visiting Sun's official Java download page. And in fact doing so will ensure you have the latest version.
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