Callable

http://www.concretepage.com/java/java-callable-example

http://www.vogella.com/tutorials/JavaConcurrency/article.html

http://www.journaldev.com/1090/java-callable-future-example

http://jovialjava.blogspot.it/2011/01/runnable-vs-callable-in-java.html

http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Callable.html