Missing basic JavaDoc in Eclipse

Question

Up to a few days ago, Eclipse was working fine in locating the javadoc for base classes such as Java.io.File. Recently, though, hovering over these classes only yields a message

Answer 1

The best way to do it is Go to Project > Properties > Java Build Path > Libraries and expand JRE System Library [your jre version] then, rt.jar. Select Source attachment, click Edit…. Select the source code file (External File…) and press OK.

Other ways to attach java source code is mentioned in this link

http://www.cavdar.net/2008/07/14/3-ways-of-jdk-source-code-attachment-in-eclipse/