import java.util.HashMap;

public class Main {
  public static void main(String[] args) {
    HashMap<String, Integer> ages = new HashMap<>();
    ages.put("Alice", 30);
    ages.put("Bob", 25);
    ages.put("Carol", 28);

    System.out.println(ages.get("Bob"));      // 25
    System.out.println(ages.containsKey("Al")); // false
    System.out.println(ages.size());          // 3
  }
}