An application programming interface (API) is a software program that facilitates interaction with other software programs.

An API allows a programmer to interact with an application using a collection of callable functions. The goal of an API is to allow programmers to write programs that will not stop working if the underlying system is updated.

Explanation of the application programming interface (API)

Think of an API as the set of the interface that establishes the rules related to a software component. When properly designed, the underlying software can be continually updated without breaking other software that depends on it.

An API can be general or specific. The complete set of a general API is included in the libraries of a programming language. With a specific API, a specific term is meant to address a specific problem.

An API is language dependent or independent:

• Language dependent: This means that it is only available by using the syntax and elements of a particular language, which makes it more convenient to use.
• Language independent: this means that the API is written to be called from various programming languages.
• Nothing kills an API faster than not having good documentation. While some developers may take a poorly documented API and figure out how it's supposed to work, most won't want to.

More generally, in the Java and OOP languages, an API generally includes a description of a set of class definitions, with a set of behaviors associated with those classes. This abstract concept is associated with the actual functionality exposed, or made available, by classes that are implemented in terms of class methods (or more generally by all their public components, hence all public methods, but also possibly including any internal entities made public as: fields, constants, nested objects, enumerations, etc.).

In this case, the API can be thought of as the totality of all the methods publicly exposed by the classes (usually called the class interface). This means that the API prescribes the methods by which one interacts with / handles objects derived from class definitions.

You should document every available API call and categorize your API calls by the type of data they act on. In addition to documenting the endpoints for the API calls themselves, you should systematically define the required and optional input arguments, as well as the output data structures. The input arguments must list a default value, if any, and also indicate the expected data format, such as a number or a string. Lastly, each API call should have a list of error conditions and status codes. https://www.restcase.com/

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In this case, the API can be thought of as the totality of all the methods publicly exposed by the classes (usually called the class interface). This means that the API prescribes the methods by which one interacts with / handles objects derived from class definitions.