su - hdfs -c "hdfs dfsadmin -report"

Java books & tutorials: 

    Introduction to Programming in Java by Robert Sedgewick and Kevin Wayne
    Oracle http://docs.oracle.com/javase/tutorial/
    Jenkos http://tutorials.jenkov.com/java/what-is-java.html
     http://mooc.cs.helsinki.fi/programming-part1
    thenewboston https://www.thenewboston.com/videos.php?cat=31
    Thinking in Java http://www.mindview.net/Books/TIJ/
    http://www.mkyong.com/featured/top-5-free-java-ebooks/
    www.kilobolt.com/unit-1-beginning-java.html
    http://learn-android-by-example.blogspot.it/2013/01/java-essentials-for-android.html

Video Tutorials

    Installing Java JDK (Windows) - https://www.youtube.com/watch?v=CijsBUrIkw4
    Installing Eclipse (Windows) - https://www.youtube.com/watch?v=9TBNEOelTeM
    Free video tutorial for learning java is https://www.udemy.com/java-tutorial

Java Web IDE/Console

    http://www.tutorialspoint.com/compile_java_online.php