Java Collections Framework

Java Collections Framework

The Java Collections Framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures. The JCF provides both interfaces and classes to manage groups of objects.

Core Interfaces

• Collection: The root interface of the collections framework.
• List: An ordered collection (also known as a sequence).
• Set: A collection that cannot contain duplicate elements.
• Queue: A collection used to hold multiple elements prior to processing.
• Map: An object that maps keys to values, cannot contain duplicate keys.

Commonly Used Classes

• ArrayList: Resizable-array implementation of the List interface.
• HashSet: Implementation of the Set interface, backed by a hash table.
• HashMap: Hash table-based implementation of the Map interface.
• LinkedList: Doubly-linked list implementation of the List and Deque interfaces.
• PriorityQueue: Implementation of the Queue interface, backed by a priority heap.

Example of Using Collections

import java.util.ArrayList;
import java.util.HashSet;
import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // ArrayList example
        ArrayList list = new ArrayList<>();
        list.add("Alice");
        list.add("Bob");
        list.add("Charlie");
        System.out.println("ArrayList: " + list);

        // HashSet example
        HashSet set = new HashSet<>();
        set.add("Alice");
        set.add("Bob");
        set.add("Alice"); // Duplicate element will be ignored
        System.out.println("HashSet: " + set);

        // HashMap example
        HashMap map = new HashMap<>();
        map.put("Alice", 1);
        map.put("Bob", 2);
        System.out.println("HashMap: " + map);
    }
}
      

The Java Collections Framework provides powerful tools for managing and manipulating groups of objects. Stay tuned for more articles and tutorials on Java programming.