URL: http://stackoverflow.com/
URL: http://www.dzone.com
URL: http://leetcode.com/
URL: http://docs.oracle.com/javase/
URL: https://github.com/
URL: https://www.coursera.org/
URL: http://www.javaworld.com/
URL: http://www.ibm.com/developerworks/java/
URL: http://en.wikipedia.org/wiki/