Apex Syntax, Data Types & Collections

1// Apex Fundamentals — Data Types & Collections
2
3public class ApexFundamentals {
4    
5    // Primitive types
6    public static void primitiveExamples() {
7        Integer count = 42;
8        Long bigNumber = 2147483648L;
9        Double pi = 3.14159;
10        Decimal price = 99.99;  // Use Decimal for money!
11        String name = 'Salesforce Developer';
12        Boolean isActive = true;
13        Date today = Date.today();
14        Datetime now = Datetime.now();
15        Id accountId = '001000000000001';  // 15 or 18 char
16        
17        // String methods
18        String upper = name.toUpperCase();
19        Boolean hasForce = name.contains('force');
20        String[] parts = name.split(' ');
21        String formatted = String.format('Hello {0}, today is {1}', 
22            new List<Object>{name, today});
23    }
24    
25    // LIST — Ordered, allows duplicates
26    public static void listExamples() {
27        // Declaration & initialization
28        List<String> fruits = new List<String>{'Apple', 'Banana', 'Cherry'};
29        
30        // Common operations
31        fruits.add('Date');                    // Add to end
32        fruits.add(1, 'Avocado');            // Insert at index
33        String first = fruits.get(0);         // Access by index
34        fruits.set(0, 'Apricot');            // Replace at index
35        Integer size = fruits.size();          // Count
36        Boolean has = fruits.contains('Banana'); // Check existence
37        fruits.sort();                         // Sort in place
38        fruits.remove(0);                      // Remove by index
39        
40        // List of SObjects (most common usage)
41        List<Account> accounts = [SELECT Id, Name FROM Account LIMIT 10];
42        
43        // Iterate
44        for (Account acc : accounts) {
45            System.debug(acc.Name);
46        }
47        
48        // List initialization from SOQL
49        List<Contact> contacts = [
50            SELECT Id, FirstName, LastName, Email
51            FROM Contact
52            WHERE AccountId IN :accountIds
53        ];
54    }
55    
56    // SET — Unordered, unique values only
57    public static void setExamples() {
58        Set<String> uniqueCities = new Set<String>();
59        uniqueCities.add('San Francisco');
60        uniqueCities.add('New York');
61        uniqueCities.add('San Francisco');  // Ignored — already exists!
62        System.assertEquals(2, uniqueCities.size());
63        
64        // Most common pattern: collecting IDs for bulk queries
65        Set<Id> accountIds = new Set<Id>();
66        for (Contact c : contacts) {
67            if (c.AccountId != null) {
68                accountIds.add(c.AccountId);
69            }
70        }
71        
72        // Use Set in SOQL WHERE IN clause
73        List<Account> relatedAccounts = [
74            SELECT Id, Name FROM Account WHERE Id IN :accountIds
75        ];
76        
77        // Set operations
78        Set<String> setA = new Set<String>{'A', 'B', 'C'};
79        Set<String> setB = new Set<String>{'B', 'C', 'D'};
80        setA.retainAll(setB);  // Intersection: {'B', 'C'}
81        // setA.addAll(setB);  // Union
82        // setA.removeAll(setB); // Difference
83    }
84    
85    // MAP — Key-value pairs (THE critical collection)
86    public static void mapExamples() {
87        // Basic Map
88        Map<String, Integer> wordCount = new Map<String, Integer>();
89        wordCount.put('apex', 5);
90        wordCount.put('soql', 3);
91        Integer count = wordCount.get('apex'); // 5
92        Boolean hasKey = wordCount.containsKey('soql'); // true
93        Set<String> allKeys = wordCount.keySet();
94        List<Integer> allValues = wordCount.values();
95        
96        // ⭐ THE MOST IMPORTANT PATTERN: Map from SOQL
97        // Initialize Map<Id, SObject> directly from query
98        Map<Id, Account> accountMap = new Map<Id, Account>(
99            [SELECT Id, Name, Industry FROM Account WHERE Industry = 'Technology']
100        );
101        
102        // Now O(1) lookup by ID!
103        Account acc = accountMap.get(someAccountId);
104        
105        // Map for parent lookup in triggers
106        Map<Id, Account> parentAccounts = new Map<Id, Account>(
107            [SELECT Id, Name FROM Account WHERE Id IN :accountIds]
108        );
109        
110        for (Contact c : Trigger.new) {
111            Account parentAcc = parentAccounts.get(c.AccountId);
112            if (parentAcc != null) {
113                // Use parent data without additional queries
114                System.debug('Contact belongs to: ' + parentAcc.Name);
115            }
116        }
117        
118        // Map with complex keys
119        Map<String, List<Contact>> contactsByCity = new Map<String, List<Contact>>();
120        for (Contact c : contacts) {
121            String city = c.MailingCity;
122            if (!contactsByCity.containsKey(city)) {
123                contactsByCity.put(city, new List<Contact>());
124            }
125            contactsByCity.get(city).add(c);
126        }
127    }
128    
129    // SObject — generic record type
130    public static void sObjectExamples() {
131        // Generic SObject usage
132        SObject record = new Account(Name = 'Test');
133        record.put('Industry', 'Technology');  // Dynamic field access
134        String name = (String) record.get('Name');
135        
136        // Get the SObject type
137        Schema.SObjectType objType = record.getSObjectType();
138        System.debug(objType); // Account
139        
140        // Cast to specific type
141        if (record instanceof Account) {
142            Account acc = (Account) record;
143            System.debug(acc.Name);
144        }
145    }
146}