Collections

In Java, the Collections Framework is a unified architecture for representing and manipulating collections of objects. It provides a set of interfaces, implementations, and algorithms to handle various types of data collections like lists, sets, and maps. The java.util package contains all the collection classes and interfaces.

Core Interfaces of Collections Framework

  1. Collection Interface:

    • The root interface of the collection hierarchy. It defines common operations like add(), remove(), size(), and clear(), which are implemented by all other collection classes.

  2. Set Interface:

    • Represents a collection of unique elements (no duplicates). Common implementations include HashSet, TreeSet, and LinkedHashSet.

  3. List Interface:

    • Represents an ordered collection that allows duplicate elements. Common implementations include ArrayList, LinkedList, and Vector.

  4. Map Interface:

    • Represents a collection of key-value pairs, where each key is unique. Common implementations include HashMap, TreeMap, and LinkedHashMap.

  5. SortedSet and SortedMap:

    • Specialized versions of Set and Map that maintain their elements in a sorted order. TreeSet implements SortedSet and TreeMap implements SortedMap.

Benefits of Using Collections Framework

  1. Efficiency:

    • Provides efficient and optimized algorithms for storing and manipulating collections.

  2. Reusability:

    • The framework allows you to reuse implementations for common data structures such as lists, sets, and maps.

  3. Flexibility:

    • The framework provides a variety of collections, each tailored to specific use cases (e.g., HashSet for fast lookups, ArrayList for dynamic arrays).

  4. Interoperability:

    • The various implementations of the core interfaces are interchangeable, allowing you to switch between them with minimal changes to your code.

Example: Using Collections to Store Data

import java.util.*;

public class CollectionsExample {
    public static void main(String[] args) {
        // Using a List to store elements
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        // Using an Iterator to iterate over the collection
        Iterator<String> iterator = names.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

🔗 Related Notes