1. What is API?

API (Application Programming Interface) is a way for two software systems to communicate with each other.

Example:

Your React frontend needs student data from a Java backend:

React → API request → Java Backend → Database
React ← API response ← Java Backend

2. What is REST?

REST (Representational State Transfer) is an architectural style for designing web APIs using HTTP.

A REST API typically works with resources such as:

/users
/products
/orders

and HTTP methods such as GET, POST, PUT, DELETE.

3. REST Principles

Important principles:

• Client-server → frontend and backend are separated.
• Stateless → server doesn't maintain client session state between requests.
• Uniform interface → consistent way of accessing resources.
• Cacheable → responses can be cached when appropriate.
• Layered system → client doesn't need to know all internal layers.
• Resource-based → APIs represent resources using URLs.