HashMap

HashMap

HashMap<K, V> stores key-value pairs with O(1) average lookup:

import java.util.HashMap;

HashMap<String, Integer> ages = new HashMap<>();
ages.put("Alice", 30);
ages.put("Bob", 25);
ages.put("Charlie", 35);

System.out.println(ages.size());           // 3
System.out.println(ages.get("Alice"));     // 30
System.out.println(ages.containsKey("Bob"));  // true
System.out.println(ages.getOrDefault("Dave", 0));  // 0

ages.put("Alice", 31);  // update existing key
System.out.println(ages.get("Alice"));  // 31
ages.remove("Bob");
System.out.println(ages.size());  // 2

Common Methods

Your Task

Create HashMap<String, Integer> of scores: Alice→95, Bob→87, Charlie→92.

1. Print its size
2. Print Alice's score
3. Print whether Bob is in the map
4. Print Dave's score with default 0
5. Update Alice's score to 98, print it