Introduction

• The Java Collections Framework consists of two main terms:
  • Collections:
    • A Collection is a single entity that stores multiple elements as a single unit.
    • Examples: List of students, set of employee IDs, map of country & capital.
  • Framework:
    • A Framework is a set of classes and interfaces that provide a consistent and reliable way to perform data handling operations.
    • Examples: Java I/O Framework, Java Concurrency Framework (Multithreading), Java Stream API (Java 8 onwards), JDBC API (Java Database Connectivity) etc.
• Definition: The Collections Framework is a unified architecture for representing and manipulating collections.
• It provides:
  • Interfaces – e.g., List, Set, Queue, Map etc.
  • Implemented Classes – e.g., ArrayList, HashSet, HashMap etc.
  • Algorithms – e.g., sorting, searching, and shuffling provided by the Collections class.
• Its main goal is to make data manipulation in Java easy, efficient, and standardized.

Hierarchy of Collections Framework

• The Collections Framework in Java contains two main interfaces:
  1. Collection – Represents a group of objects, like List, Set, or Queue.
  2. Map – Represents a collection of key-value pairs.
     • Note: Map does not extend Collection.
• Below is the hierarchy of the Collections Framework in Java:
• Tip: Some classes like Vector, Stack, Hashtable, Properties, and Dictionary are considered legacy classes but are still part of the framework for backward compatibility.
• The two main packages present in Collections Framework are:-
  1. java.util.Collection package
  2. java.util.Map package

Uses of Collections Framework

1. Storing Data:
   • Use ArrayList or LinkedList to store lists of students, products, or items.
2. Processing Queues:
   • Use Queue or Deque for tasks like managing print jobs or task scheduling.
3. Managing Unique Data:
   • Use HashSet or TreeSet to store unique elements like employee IDs.
4. Key-Value Mapping:
   • Use HashMap or TreeMap to store data in key-value pairs like country-capital mapping.
5. Sorting and Searching:
   • Collections classes provide built-in methods for sorting, searching, and shuffling data easily.

Advantages of Collections Framework

1. Reusability:
   • You can use predefined classes like ArrayList, HashMap, etc., without writing code from scratch.
2. Efficiency:
   • Collections classes are optimized for storing, retrieving, and manipulating data quickly.
3. Consistency:
   • Provides a standard way to work with data structures, so code is easier to read and maintain.
4. Flexibility:
   • Supports different types of collections like List, Set, Map for various needs.
5. Thread-Safety (optional):
   • Some collections like Vector and Hashtable are synchronized and safe for multithreaded use.