Application Programming Interface (API): Definition, Types, and Examples in Java

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📘 Application Programming Interface (API)

An Application Programming Interface (API) is a collection of interfaces, implementation classes, and helper classes that enables communication between two different applications.
APIs act as a bridge that allows one software application to interact with another without knowing its internal implementation.
An API is generally provided in the form of a JAR (Java Archive) file.
Most APIs are developed and maintained by software vendors to allow developers to use their services or features.

🔍 Example of API

✅ JDBC (Java Database Connectivity)

  • JDBC is a standard Java API
  • Used to connect Java applications with a database server
  • Allows execution of SQL queries from Java programs

🧩 Categories of API

APIs can be classified into three main categories based on how interfaces and implementations are packaged.

🔹 Category 1 API

Interface, implementation classes, and helper classes are present in a single JAR file
Easy to use and deploy
📌 Example: Core Java APIs like java.lang, java.util

🔹 Category 2 API

Consists of two JAR files

First JAR:

Interfaces
  • Partial implementation
  • Helper classes

Second JAR:

  • Remaining partial implementation of interfaces
📌 Used when implementation is split or extended separately

🔹 Category 3 API

Consists of two JAR files

First JAR:

  • Interfaces
  • Helper classes

Second JAR:

  • Complete implementation of the interfaces

📌 Example:

JDBC API
  • java.sql (interfaces)
  • Database vendor JAR (implementation like MySQL, Oracle)

⭐ Key Advantages of API

  • Enables inter-application communication
  • Promotes code reusability
  • Hides internal implementation
  • Supports loose coupling

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