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What is Java API?

What is Java API?

Harold Bell
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Java API is an application programming interface (API) that functions within software built using the Java software programming language. It’s a deep technology that plays a critical but hard-to-see role in Java applications. This article explains how Java API works, who uses it, and why.

What is Java?

The first step in understanding Java API is to get a handle on the Java language. Developed in the early 1990s at Sun Microsystems by James Gosling (later acquired by Oracle), Java was intended to provide a much-needed write-once, run-anywhere (WORA) functionality. In contrast to other programming languages at the time, which were coupled with the operating system (OS), Java enabled developers to write one Java application that could run on almost any hardware or operating system. This capability is possible due to the platform-independent Java Virtual Machine (JVM). When a user installs a JVM on his or her host OS, the JVM adapts to the host and makes it possible to run the Java software.

Though some would disagree, Java is considered by many to be the de facto standard. Much is available for free under open-source licenses. However, Java is also the programming language/environment of choice for several industry-leading developer tools. Java has many different versions, spanning consumer PCs to mobile devices and enterprise systems.

What is Java API?

Like all APIs, Java API acts as an intermediary between different elements of an information system or systems. However, Java API is different from most APIs in that its functionality is largely internal in nature. It sits in between the JVM and the Java program.

In practical terms, the Java API is integrated into the Java Development Kit (JDK). It delivers a connection interface between different Java “classes,” as pre-created Java code components are known, as well as between Java user interfaces and the underlying JVM. The Java API explains the function of each class or interface. Using Java API, a Java developer can utilize the various pre-written Java components.

Types of Java APIs

There are five types of Java APIs. The first four are the internal type described above. The fifth is more like a standard API that connects browser-based applications with external resources.

  • A public or “open” Java API is available for free as part of JDK.
  • A private Java API, also known as an “internal Java API” is created by a developer or organization for use by authorized developers.
  • A partner Java API is a third-party API that companies offer to their partners for specific use cases.
  • A composite Java API comprises microservices developed with multiple types of Java APIs.

Then, there is the Web Java API, which is accessed using HTTP with the goal of creating a connection  between browser-based apps, as well as services such as storage. The Java REST API is a variant of this approach that uses the REST architectural style to create an external interface to a Java application. It establishes a client-server architecture for the Java application and a client that wants to invoke its functionality.

Who uses Java API?

Developers are the main users of Java API, but the API is relevant to anyone who wants to access third-party services in Java. They may be internal developers, partner developers, or open developers who create APIs for open-source projects. Use cases include business-to-business (B2B) apps, business-to-consumer (B2C), app-to-app (A2A), and enterprise applications.

A wide variety of other stakeholders also use Java API, though perhaps without realizing it. For example, an enterprise architect might specify that an application have a certain kind of functionality and connectivity. He or she doesn’t care how developers make that happen, but they may be using Java API in the process.

The need for Java API

Java developers need Java APIs for a variety of reasons. In some cases, their use is unavoidable. The Java application simply requires Java API as a structural component that’s essential to its functionality. Other times, Java API enables features that realize business goals. For example, Java API enables a developer to provide an application user with multiple options on a single screen. This occurs on Facebook and LinkedIn, for example. Java API makes this possible.

More broadly, Java API becomes useful in situations where developers want to reduce the workload of the human developer. Java API facilitates automation and machine-to-machine interactions and other types of integration that occur behind the scenes. These capabilities save developers time and make it possible to generate effective applications more quickly than is possible without Java API.


Java API plays a critical role in the realization of Java applications. Often operating out of sight, Java API connects one layer of the Java programming stack to another, making the JVM perform its required functions so the Java program can do what it needs to do. Java developers use Java API across a range of use cases, many of which involve integration with other Java applications or external resources.

Harold Bell

Harold Bell is the Director of Content Marketing at Noname Security. He has over a decade of experience in the IT industry with leading organizations such as Cisco, Nutanix, and Rubrik, and has been featured as an executive ghostwriter in Forbes Technology Council and Hacker News.

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