Maps in Dart

What is a Map?

A Map stores data as key-value pairs. Each key must be unique, but values can repeat. Maps are ideal for looking up data by a meaningful label (like a dictionary or JSON object).

Creating Maps

// String keys, int values
Map<String, int> scores = {
  'Alice': 95,
  'Bob': 87,
  'Carol': 92,
};

// Dynamic values
Map<String, dynamic> user = {
  'name': 'John',
  'age': 30,
  'isAdmin': false,
};

// Empty map
var config = <String, String>{};

Accessing Values

print(scores['Alice']);      // 95
print(scores['Unknown']);    // null (key not found)

// Safe access with default
int bobScore = scores['Bob'] ?? 0;
print(bobScore);             // 87

// Check key existence
print(scores.containsKey('Carol'));   // true
print(scores.containsValue(100));     // false

Common Methods

Example

void main() {
  Map<String, int> inventory = {
    'apples': 50, 'bananas': 30, 'oranges': 20
  };

  // Add / update
  inventory['grapes'] = 15;
  inventory['apples'] = 45;

  // Iterate
  inventory.forEach((item, qty) {
    print('$item: $qty units');
  });

  // Keys and values
  print('Items: $${inventory.keys.toList()}');
  print('Total: $${inventory.values.reduce((a, b) => a + b)}');

  // Remove
  inventory.remove('bananas');
  print('After removal: $${inventory.length} items');
}

apples: 45 units
bananas: 30 units
oranges: 20 units
grapes: 15 units
Items: [apples, bananas, oranges, grapes]
Total: 110
After removal: 3 items

🧠 Quiz

Summary

Maps store key-value pairs with unique keys. Access values with map[key] (returns null if missing). Use forEach() to iterate entries. Key properties: keys, values, entries, length. Use ?? for null-safe access with defaults.