The Collections Framework: An Overview

What is the Collections Framework? It is a unified architecture for representing and manipulating collections (groups of objects). It provides a set of interfaces and classes to make storing and processing data easier and more efficient.

Core Interfaces:

• Collection: The root interface. It represents a group of objects. It is rarely used directly.

• List: An ordered collection (a sequence) that allows duplicate elements. You can access elements by their integer index. ArrayList is the most common implementation.

• Set: A collection that does not allow duplicate elements. It models the mathematical set abstraction. HashSet is the most common implementation.

• Map: An object that maps keys to values. It does not allow duplicate keys; each key can map to at most one value. HashMap is the most common implementation.

Diagram Description: A hierarchy diagram showing Collection as the root. List and Set extend Collection. Map is shown as a separate, top-level interface. Below List, show ArrayList and LinkedList. Below Set, show HashSet and TreeSet. Below Map, show HashMap and TreeMap.

// List example
List<String> myList = new ArrayList<>();
myList.add("A");
myList.add("A"); // Duplicates are allowed

// Set example
Set<String> mySet = new HashSet<>();
mySet.add("A");
mySet.add("A"); // This duplicate will be ignored

// Map example
Map<String, Integer> myMap = new HashMap<>();
myMap.put("Alice", 25);
myMap.put("Bob", 30);