MemberJuly 13, 2017 at 2:29 pm
A map is a collection of key-value pairs where each unique key maps to a single value. Keys and values can be any data type—primitive types, collections, sObjects, user-defined types, and built-in Apex types.
To declare a map, use the Map keyword followed by the data types of the key and the value within <> characters. For example:
Map<String, String> country_currencies = new Map<String, String>();
Map<ID, Set<String>> m = new Map<ID, Set<String>>();