HashMap

Store data as key-value pairs.

Import and Create

import java.util.HashMap;

HashMap<String, Integer> ages = new HashMap<>();

Common Methods

HashMap<String, Integer> map = new HashMap<>();

map.put("Alice", 25);      // Add entry
map.put("Bob", 30);
map.get("Alice");          // Get value: 25
map.remove("Bob");         // Remove entry
map.containsKey("Alice");  // true
map.containsValue(25);     // true
map.size();                // Number of entries

Looping

// Loop through keys
for (String key : map.keySet()) {
    System.out.println(key);
}

// Loop through key-value pairs
for (var entry : map.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}