Maps

Map<String, Decimal> productPrices = new Map<String, Decimal>();
productPrices.put('Widget', 49.99);
productPrices.put('Gadget', 89.99);

System.debug(productPrices.get('Widget')); // 49.99

1. Map<String, Decimal> productPrices = new Map<String, Decimal>(); — Map<String, Decimal> declares a map from String keys to Decimal values.
2. productPrices.put('Widget', 49.99); — put(key, value) adds an entry.
3. productPrices.put('Gadget', 89.99); — adds another.
4. (blank line)
5. System.debug(productPrices.get('Widget')); — get(key) retrieves the value for that key directly — no looping required — logs 49.99.

Map<String, Decimal> productPrices = new Map<String, Decimal>{'Widget' => 49.99};

if (productPrices.containsKey('Gadget')) {
    System.debug(productPrices.get('Gadget'));
} else {
    System.debug('No price found for Gadget.');
}

1. Map<String, Decimal> productPrices = new Map<String, Decimal>{'Widget' => 49.99}; — a map with only one entry.
2. (blank line)
3. if (productPrices.containsKey('Gadget')) { — containsKey() checks safely first, exactly the guard-before-use habit from Module 12's "Handle Errors Gracefully" lesson.
4. System.debug(productPrices.get('Gadget')); — only reached if the key exists.
5. } else { — the key doesn't exist here.
6. System.debug('No price found for Gadget.'); — a clean fallback, instead of calling get() on a key that doesn't exist and silently getting null back — which could lead to a confusing NullPointerException later.
7. } — closes the if/else.

// The List approach: search every item, one at a time
for (Product__c p : allProducts) {
    if (p.Name == 'Widget') {
        System.debug(p.Price__c);
        break;
    }
}

// The Map approach: direct lookup, no searching
System.debug(productPrices.get('Widget'));

1. // The List approach: search every item, one at a time — the label for what follows.
2. for (Product__c p : allProducts) { — searching a List means checking items one by one.
3. if (p.Name == 'Widget') { — until a match is found.
4. System.debug(p.Price__c); — logs it.
5. break; — stops searching once found.
6. } — closes the if.
7. } — closes the loop — slower as the list grows.
8. (blank line)
9. // The Map approach: direct lookup, no searching — the label for the alternative.
10. System.debug(productPrices.get('Widget')); — a Map looks a key up directly — why "look this up by Id" is almost always modeled as a Map in real Apex code, especially inside loops where repeated searching would be costly.