Collections in Java

What is Collections Framework in Java?

The Java Collections Framework (JCF) is a set of classes and interfaces provided by Java to store, manage, and manipulate groups of objects efficiently.

Before Collections, developers mainly used arrays. Arrays have a fixed size and limited functionality. Collections provide dynamic storage and many built-in methods for handling data.

Package: java.util

Why is Collections Used?

Collections are used to:

• Store multiple objects dynamically.
• Perform searching, sorting, insertion, and deletion easily.
• Reduce coding effort through built-in methods.
• Improve code reusability and maintainability.
• Handle large amounts of data efficiently.

Without Collections

int[] arr = new int[100];

• Fixed size
• Difficult to resize
• Limited operations

With Collections

ArrayList<Integer> list = new ArrayList<>();

• Dynamic size
• Easy insertion and deletion
• Rich utility methods

Advantages

• Dynamic Size
• Ready-Made Data Structures
• Better Performance
• Reusability and Maintainability

List Interface

• A List stores elements in insertion order and allows duplicates.

Features

• Ordered
• Duplicate elements allowed
• Index-based access

Set Interface

• A Set stores unique elements only.

Features

• No duplicates
• Usually unordered
• Faster searching

Map Interface

• Map stores data as Key-Value pairs.
• A key must be unique.

Features

• Key-Value storage
• Duplicate keys not allowed
• Values can be duplicated