HashMap & Key-Value Pairs

import java.util.HashMap;
import java.util.Map;

public class HashMapDemo {
    public static void main(String[] args) {
        // Creating a HashMap
        HashMap<String, Integer> ages = new HashMap<>();
        
        // Adding key-value pairs
        ages.put("Alice", 25);
        ages.put("Bob", 30);
        ages.put("Charlie", 28);
        ages.put("Diana", 22);
        System.out.println("Ages: " + ages);
        
        // Getting values
        System.out.println("Alice's age: " + ages.get("Alice"));
        System.out.println("Contains Bob? " + ages.containsKey("Bob"));
        
        // Default value if key not found
        System.out.println("Eve's age: " + ages.getOrDefault("Eve", -1));
        
        // Updating
        ages.put("Alice", 26);  // Overwrites old value
        System.out.println("Alice updated: " + ages.get("Alice"));
        
        // Removing
        ages.remove("Diana");
        System.out.println("After remove: " + ages);
        
        // Iterating
        System.out.println("\nAll entries:");
        for (Map.Entry<String, Integer> entry : ages.entrySet()) {
            System.out.println("  " + entry.getKey() + " → " + entry.getValue());
        }
        
        // Word frequency counter
        String text = "java is great and java is fun and java is powerful";
        String[] words = text.split(" ");
        HashMap<String, Integer> freq = new HashMap<>();
        
        for (String word : words) {
            freq.put(word, freq.getOrDefault(word, 0) + 1);
        }
        System.out.println("\nWord frequencies: " + freq);
    }
}