Iterate through a HashMap What's the best way to iterate over the items in a HashMap? solution: Iterate through the entrySet like so: public static void printMap(Map mp) { Iterator it = mp.entrySet().iterator(); while (it.hasNext()) { Map.Entry pair = (Map.Entry)it.next(); System.out.println(pair.getKey() + " = " + pair.getValue()); it.remove(); // avoids a ConcurrentModificationException } } Read more on Map http://stackoverflow.com/questions/1066589/iterate-through-a-hashmap

Differences between HashMap and Hashtable? What are the differences between a HashMap and a Hashtable in Java? Which is more efficient for non-threaded applications? Solution: There are several differences between HashMap and Hashtable in Java: Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values. One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap