A Map is collection that maps keys to values. A map cannot contain duplicate keys, each key can map to at most one value. Map comes with 4 different version - Hashtable, HashMap, TreeMap, LinkedHashMap.
Hashtable - Key methods of Hashtable are synchronized. Hashtable doesn't allow a null key or null values.
HashMap - HashMap allows one null key and multiple null values in a collection.
TreeMap - TreeMap is a sorted Map.
LinkedHashMap - LinkedHashMap maintains insertion order.
Below are the methods in which you can iterate a Map.
1. Iterator - Using Iterator you can iterate HashMap, TreeMap, LinkedHashMap.
2. Enumeration - Using Enumeration you can iterate Hashtable.
3. Also you can iterate values of a Map using values() and elements() method.
Please see the below code.
