Resource Links
https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html
https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
https://docs.oracle.com/javase/8/docs/api/java/util/HashSet.html
https://docs.oracle.com/javase/8/docs/api/java/util/TreeMap.html
https://docs.oracle.com/javase/8/docs/api/java/util/TreeSet.html