so, when I highlight a word in eclipse ide, I will get the help.
To add Javadoc to Eclipse:
You can find Java SE development kit 7 Documentation here
**You didn't specify what operating system you were on, so each OS may vary slightly.*
Right Click the JAR file in Project Explorer -> Properties -> From the left pane choose Javadoc Location -> enter the URL of your jar documentation.
Generally you can Google for:
For example Google returned this: