What is Java API and The Need for Java APIs?

Java application programming interfaces (APIs) are predefined software tools that easily enable interactivity between multiple applications.

What is Java?

Java is an object-oriented programming language that runs on almost all electronic devices and is the most common language used by web developers. Java is platform-independent because of Java virtual machines (JVMs). It follows the principle of "write once, run everywhere.” When a JVM is installed on the host operating system, it automatically adapts to the environment and executes the program’s functionalities. 

To install Java on a computer, the developer must download the JDK and set up the Java Runtime Environment (JRE). Java offers many benefits, which we will explore in detail.

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As previously noted, a Java  download consists of two files:

  • JDK
  • JRE

Installing Java is usually simple. To learn more, please see the Simplilearn article “One-Stop Solution for Java Installation in Windows.”

The JDK file is key to developing APIs in Java and consists of:

  • The compiler
  • The JVM
  • The Java API


A  Java compiler is a predefined program that converts the high-level, user-written code language to low-level, computer-understandable, byte-code language during the compile time.


A JVM  processes the byte-code from the compiler and provides an output in a user-readable format.

Java APIs

Java APIs are integrated pieces of software that come with JDKs. APIs in Java provides the interface between two different applications and establish communication.

We will learn more about Java APIs in the next section.

What Are Java APIs? 

APIs are important software components bundled with the JDK. APIs in Java include classes, interfaces, and user Interfaces. They enable developers to integrate various applications and websites and offer real-time information.

The following image depicts the fundamental components of the Java API.


Now that we know the basics of the Java API and its components, let’s explore who uses them.

Who Uses Java APIs?

Three types of developers use Java APIs based on their job or project:

  1. Internal developers
  2. Partner developers
  3. Open developers

Internal Developers

Internal developers use internal APIs for a specific organization. Internal APIs are accessible only by developers within one organization.

Applications that use internal APIs include:

  • B2B
  • B2C
  • A2A
  • B2E

Examples include Gmail, Google Cloud VM, and Instagram.

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Partner Developers

Organizations that establish communications develop and use partner APIs. These types of APIs are available to partner developers via API keys.

Applications that use partner APIs include:

  • B2B
  • B2C

Examples include Finextra and Microsoft (MS Open API Initiative),

Open Developers

Some leading companies provide access to their APIs to developers in the open-source format. These businesses provide access to APIs via a key so that the company can ensure that the API is not used illegally.

The application type that uses internal APIs is:

  • B2C

Examples include Twitter and Telnyx.

The next section explores the importance of Java APIs.

The Need for Java APIs

Java developers use APIs to:

Streamline Operating Procedures

Social media applications like Twitter, Facebook, LinkedIn, and Instagram provide users with multiple options on one screen. Java APIs make this functionality possible.

Improve Business Techniques

Introducing APIs to the public leads many companies to release private data to generate new ideas, fix existing bugs, and receive new ways to improve operations. The Twitter developer account is an example of an API that gives programmers private API keys to access Twitter data and develop applications. 

Create Powerful Applications

Online banking has changed the industry forever, and APIs offer customers the ability to manage their finances digitally with complete simplicity.

Below we discuss the various types of Java APIs.

Types of Java APIs

There are four types of APIs in Java:

  • Public
  • Private
  • Partner
  • Composite



Public (or open) APIs are Java APIs that come with the JDK. They do not have strict restrictions about how developers use them.


Private (or internal) APIs are developed by a specific organization and are accessible to only employees who work for that organization. 


Partner APIs are considered to be third-party APIs and are developed by organizations for strategic business operations.


Composite APIs are microservices, and developers build them by combining several service APIs. 

Now that we’ve covered the types of Java APIs, let’s discuss the categorization of Java APIs based on the services that different varieties of APIs in Java provide.

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Data and API Services

Data and API services are another way to categorize Java APIs other than public, private, partner, and composite. APIs are also classified based on their data-manipulation capabilities and the variety of services they offer, including:

  • Internal API services
  • External API services
  • CRUD
  • User interface services

Internal API Services

Internal API services are developed to offer organizations services specific to that organization. These services include only complex data operations and internal processes.

External API Services

External APIs are open-source APIs that developers integrate into an existing application or website.


CRUD APIs provide data manipulation operations over various data storage units such as software as a service (SaaS) and relational database management systems (RDBMS), using standard storage-unit connecting tools like Java Database Connectivity (JDBC). 

User Interface Services

User interface service APIs are open-source APIs that allow developers to build user interfaces for mobile devices, computers, and other electronics.

Next, let’s examine the rules and protocols that Java APIs follow.

API Service Protocols

The rules and protocols guide the functionality of the Java API. Different APIs have different service protocols. Let’s consider an example of RESTful API service protocol as an example.

For a typical RESTful API, developers must follow these rules:

  • Stateless
  • Uniform interface
  • Client-server
  • Cache
  • Layered


A RESTful API follows client-server architecture so it must be stateless.

Uniform Interface

The entities in a RESTful API are the server and clients. Applications that run on a global scale need a uniform client and server interface through the Hypertext Transfer Protocol (HTTP). Uniform Resource Identifiers (URIs) allocate the required resources. 


The client-server model used in the RESTful API should be fault-tolerant. Both the client and server are expected to operate independently. The changes made at the client end should not affect the server end and vice versa.


Including a cache memory allows the application to record intermediate responses and run faster in real-time. A RESTful API also includes the cache memory.  


A RESTful API is built using layers. Layers in the API are loosely coupled, or independent, from each other. Each layer contributes to a different level of hierarchy and also supports encapsulation.

 Next we’ll go over the most frequently used Java APIs.

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The Most Commonly Used Java APIs













Java Advanced Imaging


Java Data Objects


Java Media Frameworks


Java Persistence API


Java Speech API


Java 3D


Java USB for Windows


Android API


Association of the Standardization of Embedded Platforms

ESR Consortium

Java Naming and Directory Interface


Next, let’s examine the significant advantages of APIs in Java.

The Advantages of APIs

Some of the main advantages of using Java APIs include:

Advantage of Java API

Extensive SQL Support

APIs in Java enable a wide range of SQL support services in user applications through a component-based interface.


APIs in Java provide effortless access to all of an application’s major software components and easily deliver services.


Java APIs are highly efficient because they enable rapid application deployment. Also, the data that the application generates is always available online. 


APIs allow computers to automatically upload, download, update and delete data automatically without human interaction.


Java APIs can integrate into any application and website and provide a fluid user experience with dynamic data delivery.  


Java APIs easily make websites, applications, and information available to a wide range of users and audiences.


Java APIs enable developers and businesses to build applications that personalize the user interface and data.


Java APIs are highly flexible and adaptable because they can easily accept feature updates and changes to frameworks and operating environments.

Next Steps

Java APIs are useful in real-time website and application development. Now that you have a good understanding of APIs in Java, the next step is to learn How to become a Software Developer, with Simplilearn's Full Stack Developer - MEAN Stack course. 

If you're looking for more in-depth knowledge about the Java programming language and information on how to get certified as a professional developer, explore our Java training and certification programs, which Simplilearn’s experienced industry experts offer in real-time. In particular, check out our Caltech Coding Bootcamp today!

If you have any questions about this article, please leave them in the comments section, and our experts will quickly answer them.

About the Author

Ravikiran A SRavikiran A S

Ravikiran A S works with Simplilearn as a Research Analyst. He an enthusiastic geek always in the hunt to learn the latest technologies. He is proficient with Java Programming Language, Big Data, and powerful Big Data Frameworks like Apache Hadoop and Apache Spark.

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