Few considerations to be taken are here:
-
If you're using maven for your dependency management, you should be able to expand out the list of Maven dependencies in your Eclipse project, right click the hadoop-core-x.x.x.jar and select Maven -> Download Javadocs
-
Otherwise you'll need to source the Javadocs from the $HADOOP_HOME/docs/api folder and associated with your hadoop-core-x.x.x.jar in Eclipse. In Eclipse, right click your Java project and select Build Path -> Configure Build Path. Now click the Libraries tab and locate the entry for hadoop-core-x.x.x.jar. Expand the entry to show options for Source, Javadoc etc locations and click the Javadoc location entry. Now click the Edit button to the right and enter the location as the path $HADOOP_HOME/docs/api in the Javadoc URL text box (mine is file:/opt/hadoop/hadoop-1.0.2/docs/api/)
Either way now you should be able to hover over Hadoop classes in Eclipse and the Javadoc will popup. You can also show the Javadoc window that will populate for the class you are currently viewing, or just open an internal browser window and point it at the $HADOOP_HOME/docs/api/index.html file