Collections

        
          import java.util.*;

public class CollectionsDemo {
    public static void main(String[] args) {
        // ArrayList - dynamic array
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        System.out.println("Names: " + names);
        System.out.println("First name: " + names.get(0));

        // LinkedList - doubly linked list
        List<Integer> numbers = new LinkedList<>();
        numbers.add(10);
        numbers.add(20);
        numbers.addFirst(5);
        numbers.addLast(30);

        // HashSet - unique elements
        Set<String> uniqueNames = new HashSet<>();
        uniqueNames.add("Alice");
        uniqueNames.add("Bob");
        uniqueNames.add("Alice"); // Duplicate, won't be added

        System.out.println("Unique names: " + uniqueNames);

        // HashMap - key-value pairs
        Map<String, Integer> ages = new HashMap<>();
        ages.put("Alice", 25);
        ages.put("Bob", 30);
        ages.put("Charlie", 35);

        System.out.println("Alice's age: " + ages.get("Alice"));

        // Iterating over collections
        System.out.println("All ages:");
        for (Map.Entry<String, Integer> entry : ages.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }

        // Enhanced for loop
        System.out.println("All names:");
        for (String name : names) {
            System.out.println(name);
        }

        // Using streams (Java 8+)
        List<Integer> evenNumbers = numbers.stream()
            .filter(n -> n % 2 == 0)
            .collect(Collectors.toList());

        System.out.println("Even numbers: " + evenNumbers);

        // Sorting
        Collections.sort(names);
        System.out.println("Sorted names: " + names);

        // Queue and Stack
        Queue<String> queue = new LinkedList<>();
        queue.offer("First");
        queue.offer("Second");
        System.out.println("Queue poll: " + queue.poll());

        Deque<String> stack = new ArrayDeque<>();
        stack.push("Bottom");
        stack.push("Top");
        System.out.println("Stack pop: " + stack.pop());
    }
}