Cannot instantiate the type Set

Question

I am trying to create a Set of Strings which is filled with the keys from a Hashtable so a for-each loop can iterate through the Set and put defaults in a Hashtable. I am still learning Java but the way I am trying to do it isn't valid syntax. Could someone please demonstrate the proper way of doing this and explain why my way doesn't work and theirs does.

private Hashtable<String, String> defaultConfig() {     Hashtable<String, String> tbl = new Hashtable<String, String>();     tbl.put("nginx-servers","/etc/nginx/servers");     tbl.put("fpm-servers","/etc/fpm/");     tbl.put("fpm-portavail","9001");     tbl.put("webalizer-script","/usr/local/bin/webalizer.sh");     tbl.put("sys-useradd","/sbin/useradd");     tbl.put("sys-nginx","/usr/sbin/nginx");     tbl.put("sys-fpmrc","/etc/rc.d/php_fpm");     tbl.put("www-sites","/var/www/sites/");     tbl.put("www-group","www");      return tbl; }  //This sets missing configuration options to their defaults. private void fixMissing(Hashtable<String, String> tbl) {     Hashtable<String, String> defaults = new Hashtable<String, String>(defaultConfig());     //The part in error is below...     Set<String> keys = new Set<String>(defaults.keySet());      for (String k : keys) {         if (!tbl.containsKey(k)) {             tbl.put(k, defaults.get(k));         }     } } 

Answer 1

Set is not a class, it is an interface.

So basically you can instantiate only class implementing Set (HashSet, LinkedHashSet orTreeSet)

For instance :

Set<String> mySet = new HashSet<String>();