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6) Collections in Apex.md

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6) Collections in Apex.md

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1. List Datatype

NOTE: List index starts from 0. List is an ordered collection.

List<Integer> rollNumbers = new List<Integer>{11008890, 11008100, 11007231}; System.debug(rollNumbers); // (11008890, 11008100, 11007231)

rollNumbers.add(89897767); rollNumbers.add(89897764); rollNumbers.add(89897765);

System.debug(rollNumbers); // (11008890, 11008100, 11007231, 89897767, 89897764, 89897765)

get item on index 1

Integer rollNum = rollNumbers.get(1); System.debug(rollNum); // 11008100

NOTE: short way to write a code System.debug(rollNumbers.get(1)); //11008100

add item on index 4

rollNumbers.add(4, 99990000); System.debug(rollNumbers); // (11008890, 11008100, 11007231, 89897767, 99990000, 89897764, 89897765)

get the list size -it shows how many items in it

System.debug(rollNumbers.size()); // 7

remove the item on index 3

rollNumbers.remove(3); System.debug(rollNumbers); // (11008890, 11008100, 11007231, 99990000, 89897764, 89897765)

System.debug(rollNumbers.size()); // 6

update item on index 1

rollNumbers.set(1, 44444444); System.debug(rollNumbers); // (11008890, 44444444, 11007231, 99990000, 89897764, 89897765)

clear the list

rollNumbers.clear(); System.debug(rollNumbers); // {} System.debug(rollNumbers.size()); // 0

below line will throw an error

rollNumbers.set(1, 44444444); System.debug(rollNumbers);

2. Set Datatype

NOTE: It directly stores your data without the indexes. So, that's why we call it unordered collection of elements. The most important property of a set is, it doesn't allow Duplicate Data. Unlike list, set doesn't have any indexes. It simply stores your data as it is without any indexes. And if you want to get an item, it will directly get it by its value. So, in list, we used to get an item by its index.

Set<Integer> rollNumbers = new Set<Integer>{11008890, 11008100, 11007231}; System.debug(rollNumbers); // {11007231, 11008100, 11008890}

rollNumbers.add(89897767); rollNumbers.add(89897764);
rollNumbers.add(89897765);

System.debug(rollNumbers); // {11007231, 11008100, 11008890, 89897764, 89897765, 89897767}

adding duplicate values - NOT ALLOWED

rollNumbers.add(89897767); System.debug(rollNumbers); // {11007231, 11008100, 11008890, 89897764, 89897765, 89897767}

check if set has an item (contains - true or false)

System.debug(rollNumbers.contains(89897764)); // true System.debug(rollNumbers.contains(345345));

delete an item

rollNumbers.remove(89897765); System.debug(rollNumbers); // false

get set size

System.debug(rollNumbers.size()); // 5

check if set is empty (isEmpty - true or false)

System.debug(rollNumbers.isEmpty()); // false

remove all items

rollNumbers.clear(); System.debug(rollNumbers.isEmpty()); // true

2. Map Datatype

NOTE: It stores the data in a key value pair.

Map<Integer, String> class2020 = new Map<Integer, String>();

add a new student/item.

NOTE: to add a new item in a map, we need to use the 'put' method. In the set and list, we use the 'add' method.

class2020.put(11008890, 'Smith'); System.debug(class2020); //{11008890=Smith}

class2020.put(11008891, 'Harry'); class2020.put(11008892, 'Rick'); class2020.put(11008893, 'Bill');

System.debug(class2020); // {11008890=Smith, 11008891=Harry, 11008892=Rick, 11008893=Bill}

class2020.put(11008894, 'Bill'); System.debug(class2020); // {11008890=Smith, 11008891=Harry, 11008892=Rick, 11008893=Bill, 11008894=Bill}

update/override value

class2020.put(11008894, 'Skywalker'); System.debug(class2020); // {11008890=Smith, 11008891=Harry, 11008892=Rick, 11008893=Bill, 11008894=Skywalker}

get a value

System.debug(class2020.get(11008892)); // Rick

remove an item from map

class2020.remove(11008893); System.debug(class2020); // {11008890=Smith, 11008891=Harry, 11008892=Rick, 11008894=Skywalker}

get all the keySet

Set<Integer> rollNumber = class2020.keySet(); System.debug(rollNumber); // {11008890, 11008891, 11008892, 11008894}

get all the values

List<String> students = class2020.values(); System.debug(students); // (Smith, Harry, Rick, Skywalker)

check if map has the key

System.debug(class2020.containsKey(11008892)); // true

System.debug(class2020.containsKey(11008893)); // false

Challenge

posts for apple category

List<String> applePosts = new List<String>{'Demystifying ios Collections', 'Datatypes and variables in IOS'};

posts for lightning category

List<String> samsungPosts = new List<String>{'Events in android framework', 'Developing reusable components'};

map to store the categories and post lists

Map<String, List<String>> allPosts = new Map<String, List<String>>();

insert apex posts

allPosts.put('Apple', applePosts); // insert lightning posts allPosts.put('Samsung', samsungPosts);

printing all posts along with categories

System.debug(allPosts); // {Apple=(Demystifying ios Collections, Datatypes and variables in IOS), Samsung=(Events in android framework, Developing reusable components)}