Salesforce with Ankit

In this article we will cover three collections in Apex (Lists, Sets, & Maps). Also we will see some examples of them.

1. Introduction –
   • Collection in any data-type is where we have more than one value stored together for use.
   • Collections are useful in triggers as bulkification is needed in triggers. (Need to process in batch of 200 records).
   • Collection is also helpful in processing big amount of data.
2. Lists –
   • A list in Apex is analogous to an array in other programming languages, that it is an ordered list of items that can be referred by their index.
   • Declaration of list:
     • List<data-type> myList = new List<data-type> ( );
   • Adding element to list:
     • myList.add(‘Item1’);
   • Reading element from list:
     • using index. For example: myList[0] will return Item1.
   • Using get :
     • data-type s = compass.ger(0); [Sets s to be Item1]
   • List also stores duplicate data.
3. Sets –
   • A set is unordered collection of unique items with no duplicates.
   • Declaration of Sets:
     • Set<String> myStringSet = new Set<String> ( );
   • We cannot access element in set using index.
   • To check whether elements is present in set or not, we can use Boolean function ( contains ), which will return true if element is present and false if element is not there.
4. Maps –
   • Maps are collection of key-value pairs, that allows us to store a variety of data-types using a key of any data-type, rather than integer as index.
   • Declaration of maps:
     • Map<key-type,value-type> mapName = new Map<key-type,value-type> ( );
   • The keys within Map must be unique.
   • Since key are unique and values can be any, we can use set as a key of map and List as values in following way:
     • Map<String,Integer> ageMap = new Map <String,Integer> ( );
     • Set<String> names = ageMap.keySet ( );
     • List<Integer> ages = ageMap.values ( );

Thank you for reading the article till the end, in next article we will discuss about Operators.