Many Mac OS/X Lion users are noticing that when they upgrade their operating system, their Eclipse install breaks and says that Java is needed to run.
Lion does not ship with a Java Runtime by default.
To fix your Eclipse or MyEclipse install:
1. Go to the Apple site to download the Java SE JDK installer.
2. Install the JDK.
3. Restart Eclipse or MyEclipse.
You should be good to go!
Update, thanks to Riyad:
You can open a Terminal window and type "java" and OS X will invoke an automatic GUI install of it for you.
Additionally, even if you had Java installed in the previous version of Mac before applying the big update, the update will actually *remove* it. So, even if Java was installed previously, you'll have to do it again.