Hello Trailblazers,

// * Collections in Apex

/*
*   There are 3 types of collections in apex:
*   1. List
*   2. Set
*   3. Map
*/

// * List - Part 1

// * List: A list is an ordered collection of elements. We can create a list of any data type like: primitive data types, collections, sObjects, custom data types etc.

// * Creating a list of names
List<String> names = new List<String>();
names.add('Richard Hendricks');
names.add('Monica');
names.add('Erlich Bachman');
names.add('Dinesh');
names.add('Gilfoyle');

System.debug('Names = ' + names);

// * Retrieving an element from the list
System.debug('Element at index 2 = ' + names[2]);

// * Replacing a list element at a particular index
names.set(2, 'Gavin Belson');
System.debug('Updated Names = ' + names);

names[2] = 'Erlich Bachman';
System.debug('Updated Names = ' + names);

// * Setting an index that doesn't exist
// names.set(10, 'Jared Dunn');

// names[10] = 'Jared Dunn';

// * Displaying the size of the list
System.debug('Size of list "names" = ' + names.size());

// * Clearing the list
names.clear();

System.debug('Size of list "names" = ' + names.size());
System.debug('Updated Names = ' + names);

// * List - Part 2

// * Checking if the list is empty
List<Integer> numbers = new List<Integer>();
System.debug('Numbers List = ' + numbers);
System.debug('Numbers List is empty = ' + numbers.isEmpty());

numbers.add(1);
numbers.add(2);

System.debug('Numbers List = ' + numbers);
System.debug('Numbers List is empty = ' + numbers.isEmpty());

// * Defining lists using array notation
String[] names = new String[5];
// List<String> names = new String[5];
// String[] names = new List<String>();
names[2] = 'Gavin Belson';
names[4] = 'Jared Dunn';
names[0] = 'Richard Hendricks';
names[1] = 'Erlich Bachman';
names[3] = 'Monica';
// names.add('Gavin Belson');
System.debug('Names Array = ' + names);
System.debug('Size of list "names" = ' + names.size());

// names[5] = 'Dinesh Chugtai';

names.add('Dinesh Chugtai');

System.debug('Updated Names = ' + names);
System.debug('Size of list "names" = ' + names.size());

// * Populating values inside a list at the time of initialization
List<String> names = new List<String>{'SFDC Stop', 'Rahul Malhotra'};
System.debug('Initial Names = ' + names);

String[] names = new String[]{'SFDC Stop', 'Rahul Malhotra'};
System.debug('Initial Names = ' + names);

// * List - Part 3

// * Sorting a list
List<String> names = new List<String>{'Richard Hendricks', 'Erlich Bachman', 'Gavin Belson', 'Monica', 'Jared Dunn', ''};
System.debug('Names = ' + names);
names.sort();
System.debug('Names in ascending order = ' + names);

// * Creating a list of collections
List<List<String>> names = new List<List<String>>(); // * Upto 8 levels
names.add(new List<String>{'Aman', 'Ashish', 'Adam', 'Anika'});
names.add(new List<String>{'Bob', 'Bhanu', 'Blake', 'Benjamin'});
System.debug('Names = ' + names);
System.debug('Names starting with "A" = ' + names[0]);
System.debug('Names starting with "B" = ' + names[1]);
System.debug('2nd name starting with "A" = ' + names[0][1]);
System.debug('3rd name starting with "B" = ' + names[1][2]);

// * Set

// * Set: A set is an unordered collection of elements that do not contain any duplicates. We can create a set of any data type like: primitive data types, collections, sObjects, custom data types etc.

// * Creating a set of integers
Set<Integer> numbers = new Set<Integer>();
numbers.add(2);
numbers.add(1);
numbers.add(4);
numbers.add(5);
numbers.add(3);

System.debug('Numbers Set = ' + numbers);
System.debug('Number of elements in Set = ' + numbers.size());

// * Adding duplicate elements inside set
numbers.add(1);
numbers.add(5);

System.debug('Numbers Set after adding duplicate elements = ' + numbers);
System.debug('Number of elements in Set = ' + numbers.size());

// * Check if 3 is present in set
System.debug('Is 3 present inside set = ' + numbers.contains(3));

// * Removing 3 from set
System.debug('Removing 3 from set...');
numbers.remove(3);

// * Check if 3 is present in set
System.debug('Is 3 present inside set = ' + numbers.contains(3));

System.debug('Numbers Set after removing 3 = ' + numbers);
System.debug('Number of elements in Set = ' + numbers.size());

// * Populating values inside a set at the time of initialization
Set<String> fruits = new Set<String>{'Mango', 'Apple', 'Banana', 'Pear', 'Mango'};
System.debug('Elements inside set of fruits = ' + fruits);

// * Map - Part 1

// * Map: A map is a collection of key-value pairs where each unique key maps to a single value. Keys and Values inside a map can be of any data type like: primitive data types, collections, sObjects, custom data types etc.

// * Creating a map of Integer, String:

Map<Integer, String> studentsMap = new Map<Integer, String>();
studentsMap.put(3, 'Gilfoyle');
studentsMap.put(5, 'Monica');
studentsMap.put(1, 'Richard Hendricks');
studentsMap.put(2, 'Dinesh');
studentsMap.put(4, 'Erlich Bachman');
studentsMap.put(null, 'Jared Dunn');

System.debug('Value of studentsMap = ' + studentsMap);
System.debug('Total number of elements inside studentsMap = ' + studentsMap.size());

// * Getting value from a map
System.debug('Student with roll number 3 = ' + studentsMap.get(3));

// * Updating value inside a map
System.debug('Assigning a new name to roll number 3');
studentsMap.put(3, 'Gavin Belson');

System.debug('Student with roll number 3 = ' + studentsMap.get(3));
System.debug('Value of studentsMap = ' + studentsMap);

// * Removing value from a map
studentsMap.remove(3);
System.debug('Value of studentsMap after removing student with roll number 3 = ' + studentsMap);
System.debug('Total number of elements inside studentsMap = ' + studentsMap.size());

// * Map - Part 2

Map<Integer, String> studentsMap = new Map<Integer, String>();
studentsMap.put(5, 'Monica');
studentsMap.put(1, 'Richard Hendricks');
studentsMap.put(2, 'Dinesh');
studentsMap.put(4, 'Erlich Bachman');
studentsMap.put(null, 'Jared Dunn');

// * Check if the map contains a key
System.debug('Does studentsMap contain roll number 4? ' + studentsMap.containsKey(4));
System.debug('Does studentsMap contain roll number 3? ' + studentsMap.containsKey(3));

System.debug('Value of studentsMap = ' + studentsMap);
System.debug('Total number of elements inside studentsMap = ' + studentsMap.size());

// * Check if map is empty
System.debug('Is student map empty? ' + studentsMap.isEmpty());

// * Remove all elements from the map
System.debug('Clearing elements inside studentsMap...');
studentsMap.clear();

// * Check if map is empty
System.debug('Is student map empty? ' + studentsMap.isEmpty());

System.debug('Value of studentsMap = ' + studentsMap);
System.debug('Total number of elements inside studentsMap = ' + studentsMap.size());

// * Getting KeySet and Values from the map
Map<Integer, String> studentsMap = new Map<Integer, String>();
studentsMap.put(1, 'Richard Hendricks');
studentsMap.put(2, 'Dinesh');
studentsMap.put(3, 'Gilfoyle');
studentsMap.put(4, 'Erlich Bachman');
studentsMap.put(2, 'Monica');
studentsMap.put(6, 'Dinesh');

System.debug('Value of studentsMap = ' + studentsMap);
System.debug('Total number of elements inside studentsMap = ' + studentsMap.size());

Set<Integer> keys = studentsMap.keySet();
System.debug('Keys of studentsMap = ' + keys);

List<String> studentNames = studentsMap.values();
System.debug('Values of studentsMap = ' + studentNames);

// * Variables & Data Types in Apex

/*

? What is a variable?
* A variable is simply a named storage/memory location that contains a value. In apex, all variables have a "data type".
! Each variable is by default initialized to null

? What is a Data Type?
* Data type is a keyword associated with a variable. It basically represents the type of data which that variable will store.
* List of primitive data types:
* 1. Boolean
* 2. Integer
* 3. Decimal
* 4. Double
* 5. Long
* 6. Date
* 7. Datetime
* 8. Time
* 9. Id
* 10. String
* 11. Object
* 12. Blob

* These are the OOTB or fundamental data types available in apex programming language. Let's talk about each one of them in detail:

? What is a Boolean data type?
* A variable of Boolean data type can store only one of these two values:
* 1. True
* 2. False

* Example of Boolean data type:
*/

/*
one
two
three

*/

// comment

// * In order to declare a variable, we follow the format: <Data Type><space><Variable name><;>
Boolean isQualified;
System.debug('Value of isQualified boolean variable is: ' + isQualified);

isQualified = false; // * Equals (=) means Assignment
System.debug('Value of isQualified boolean variable is: ' + isQualified);

isQualified = true;
System.debug('Value of isQualified boolean variable is: ' + isQualified);

// isQualified = 123;

/*

? What is an Integer data type?
* An Integer data type can store a 32-bit number with no decimal point. It can store value between -2,147,483,648 to 2,147,483,647

* Example of Integer data type:

*/

Integer sum;
System.debug('Value of sum Integer variable is: ' + sum);

sum = 1;
System.debug('Value of sum Integer variable is: ' + sum);

sum = 10;
System.debug('Value of sum Integer variable is: ' + sum);

sum = 2147483647;
System.debug('Value of sum Integer variable is: ' + sum);

sum = -2147483647;
System.debug('Value of sum Integer variable is: ' + sum);

// sum = false;

/*

? What is a Decimal data type?
* A Decimal data type variable can store a number with a decimal point.

* Example of Decimal data type:

*/

Decimal sum;
System.debug('Value of sum Decimal variable is: ' + sum);

sum = 1.0;
System.debug('Value of sum Decimal variable is: ' + sum);

sum = 1.01;
System.debug('Value of sum Decimal variable is: ' + sum);

sum = 1.234567890123456789012345678901234567890123456789;
System.debug('Value of sum Decimal variable is: ' + sum);

sum = -123456789012345678901234567890123456789012345678.9;
System.debug('Value of sum Decimal variable is: ' + sum);

//* Help Article about the field: https://help.salesforce.com/s/articleView?id=000387302&type=1, however we can have 49 digits in total for a variable of type decimal

// * Assiging integer to a decimal
sum = 123;
System.debug('Value of sum Decimal variable is: ' + sum);

// sum = true;

/*
? What is a Double data type?
* A Double data type variable can store a 64-bit number with a decimal point. It can store value between -2^63 to 2^63-1
* Example of Double data type:
*/

Double sum = 3.14;
System.debug('Value of sum Double variable is: ' + sum);

// * Use Double for less precision. For example: Scientific calculations where rounding off can be done. Use Decimal for more precision. For example: Financial calulations where there are no chances of errors. By default, currency fields in Salesforce are stored as decimals.

/*
? What is a Long data type?
* A Long data type variable can store a 64-bit number without a decimal point. It can store value between -2^63 to 2^63-1.
* Example of Long data type:
*/

Long long1 = 1000000000;  // * Valid long value without "L"
Long long2 = 9223372036854775807L;  // * Valid long value with "L" (for clarity)
System.debug('Value of long1 Long variable is: ' + long1);
System.debug('Value of long2 Long variable is: ' + long2);

// * Long can be used when we need a higher range as compared to an integer

/*
? What is a Date data type?
* A Date data type variable can store a date value without any information about time.
* Example of Date data type:
*/

Date date1 = Date.newInstance(1994, 12, 26);
System.debug('Value of date1 Date variable is: ' + date1);
System.debug('Subtracting 1 from date1 variable. Updated value = ' + (date1 - 1));
System.debug('Adding 1 to date1 variable. Updated value = ' + (date1 + 1));

Date dateFromString = Date.valueOf('1994-12-26');
System.debug('Value of dateFromString Date variable is: ' + dateFromString);

System.debug('Date in string without timestamp is: ' + String.valueOf(dateFromString));

System.debug('Today\'s Date is: ' + System.today());

// * Adding two date values
Date date1 = Date.newInstance(1994, 12, 26);
Date date2 = Date.newInstance(1994, 12, 20);
System.debug(date1 + date2);

/*
? What is a Datetime data type?
* A Datetime data type variable can store a datetime value like a timestamp.
* Example of Datetime data type:
*/

Datetime date1 = Datetime.newInstance(1994, 12, 26);
System.debug('Value of date1 Datetime variable is: ' + date1);

Datetime dateFromString = Datetime.valueOf('1994-12-26 23:11:10'); // GMT + 5:30
System.debug('Value of dateFromString Datetime variable is: ' + dateFromString);

System.debug('Date in string without timestamp is: ' + String.valueOf(dateFromString));

/*
? What is a Time data type?
* A Time data type variable can store a time value which indicates a particular time.
* Example of Time data type:
*/

Time time1 = Time.newInstance(14, 25, 60, 100);
System.debug('Value of time1 Time variable is: ' + time1);
System.debug('Value of hour: ' + time1.hour());
System.debug('Value of minute: ' + time1.minute());
System.debug('Value of second: ' + time1.second());
System.debug('Value of millisecond: ' + time1.millisecond());

/*
? What is a ID data type?
* An ID data type variable can store any valid 18-character salesforce record id.
* Example of ID data type:
*/

Id accountId = '001Hy00001D07fwIAB';
System.debug('Value of Id accountId = ' + accountId);

Id accountIdFifteenDigits = '001Hy00001D07fw';
System.debug('Value of Id accountIdFifteenDigits = ' + accountIdFifteenDigits);

accountId = '123456789123456789';

/*
? What is a String data type?
* A String data type variable can store any set of characters surrounded by single quotes. It has no limit on the number of characters, heap size limit is used instead
* Example of String data type:
*/

String name = 'SFDC Stop';
System.debug('Value of String name = ' + name);

String nameWithTrailingWhitespace = 'SFDC Stop   ';
System.debug('Value of String nameWithTrailingWhitespace = ' + nameWithTrailingWhitespace);

String emptyStringWithWhitespace = '     ';
System.debug('Value of String emptyStringWithWhitespace = ' + emptyStringWithWhitespace);

String escapeSequence = '\nSFDC\tStop \\ A blog about salesforce';
System.debug('Value of String escapeSequence = ' + escapeSequence);

String a = 'apple', b = 'mango';
System.debug(a<b);

String c = 'sfdc', d = 'Sfdc';
System.debug(c==d);

/*
? What is a Object data type?
* An Object data type variable can store value of any data type that is supported in apex. All data types inherit from object
* Example of Object data type:
*/

Object num = 10;
System.debug('Value of Object num = ' + num);

Object name = 'SFDC Stop';
System.debug('Value of Object name = ' + name);

Object num1 = 10, num2 = 20;
System.debug('Sum of Object num1 and num2 = ' + (num1 + num2));

Object num1 = 10, num2 = 20;
Integer num1Int = (Integer) num1, num2Int = (Integer) num2;
System.debug('Sum of Integer num1Int and num2Int = ' + (num1Int + num2Int));

/*
? What is a Blob data type?
* An Blob data type variable can store a collection of binary data as a single object. Blob is the short form for Binary Large Object.
* Example of Blob data type: Contents of an image. Blob can be converted to a String and String can be converted to a Blob
*/

Blob b1 = Blob.valueOf('test');
System.debug('Value of Blob b1 = ' + b1);

System.debug('Value of Blob b1 as string = ' + b1.toString());

YouTube Tutorials

Building Blocks of Apex: Variables & Data Types Explained Simply - Salesforce Apex Tutorial Part 2

Apex Gotchas! Common Variable Errors (and Writing Comments) - Salesforce Apex Tutorial Part 3

Apex Integer Data Types: Understanding Limits & Avoiding Errors - Salesforce Apex Tutorial Part 4

Unlock Precision in Apex: The Beginner Guide to Decimal Data Type - Salesforce Apex Tutorial Part 5

Apex Double, Long, Date, Datetime & Time Data Types Explained - Salesforce Apex Tutorial Part 6

Apex Id, String, Object and Blob Data Types Decoded - Salesforce Apex Tutorial Part 7