? Java Collections Framework

? Quick Overview

The Java Collections Framework (JCF) is a unified architecture that provides ready-made classes and interfaces to store, manipulate, and process groups of objects efficiently.

? Key Concepts

Stores objects dynamically (no fixed size)
Provides standard data structures like List, Set, and Map
Reduces programming effort and improves performance
Part of java.util package

? Interactive ArrayList Visualizer

Type a value to add(). Click an item to remove().

List is empty

Size: 0

? Core Interfaces

List – Ordered, allows duplicates
Set – Unordered, no duplicates
Queue – FIFO based structure
Map – Key-value pairs

? Syntax & Theory

Collection interfaces define behavior, while concrete classes like ArrayList, HashSet, and HashMap provide implementations.

? View Code Example

// Importing the Collections package
import java.util.*;

// Main class
class CollectionDemo {
public static void main(String[] args) {
// Creating a List using ArrayList
List names = new ArrayList<>();

names.add("Java");
names.add("Python");
names.add("C++");

// Printing the list
System.out.println(names);
}
}

? Output Explanation

The ArrayList stores elements in insertion order. When printed, all added elements appear sequentially.

✅ Tips & Best Practices

Use interfaces (List, Set) instead of concrete classes
Choose the right collection based on use case
Avoid unnecessary synchronization

? Try It Yourself

Create a Set to store unique numbers
Use a Map to store student name and marks
Replace ArrayList with LinkedList and observe behavior