PROGRAMMING LANGUAGES
An API is usually related to a software library: the API describes and prescribes the expected behavior (a specification) while the library is an actual implementation of this set of rules. A single API can have multiple implementations (or none, being abstract) in the form of different libraries that share the same programming interface. The separation of the API from its implementation can allow programs written in one language to use a library written in another. For example, because Scala and Java compile to compatible bytecode, Scala developers can take advantage of any Java API. 95 Words
API use can vary depending on the type of programming language involved. An API for a procedural language such as Lua could primarily consist of basic routines to execute code, manipulate data, or handle errors, while an API for an object oriented language such as Java would provide a specification of classes and their class methods. 56 Words
Language bindings are also APIs. By mapping the features and capabilities of one language to an interface implemented in another language, a language binding allows a library or service written in one language to be used when developing in another language. Tools such as SWIG and F2PY, a Fortran to Python interface generator, facilitate the creation of such interfaces. 60 Words
Remote APIs allow developers to manipulate remote resources through protocols, specific standards for communication that allow different technologies to work together, regardless of language or platform. For example, the Java Database Connectivity API allows developers to query many different types of databases with the same set of functions, while the Java remote method invocation API uses the Java Remote Method Protocol to allow invocation of functions that operate remotely, but appear local to the developer. Therefore, remote APIs are useful in maintaining the object abstraction in object-oriented programming; a method call, executed locally on a proxy object, invokes the corresponding method on the remote object, using the remoting protocol, and acquires the result to be used locally as return value. A modification on the proxy object will also result in a corresponding modification on the remote object. 137 Words
The design of an API has significant impacts on its usability. The principle of information hiding describes the role of programming interfaces as enabling modular programming by hiding the implementation details of the modules so that users of modules need not understand the complexities inside the modules. Thus, the design of an API attempts to provide only the tools a user would expect. The design of programming interfaces represents an important part of software architecture, the organization of a complex piece of software. 83 Words
When parts of a publicly presented API are subject to change and thus not stable, such parts of a particular API should be explicitly documented as unstable. For example, in the Google Guava library the parts that are considered unstable, and that might change in a near future, are marked with the Java annotation @Beta. 55 Words
A public API can sometimes declare parts of itself as deprecated. This usually means that such part of an API should be considered candidates for being removed, or modified in a backward incompatible way. Therefore, deprecation allows developers to transition away from parts of the API that will be removed or unsupported in the future. 55 Words
API documentation describes what services an API offers and how to use those services, aiming to cover everything a client would need to know to use the API. Documentation is crucial for the development and maintenance of applications that use the API. API documentation is traditionally found in documentation files, but can also be found in social media such as blogs, forums, and Q&A websites. Traditional documentation files are often presented via a documentation system, such as Javadoc or Pydoc, that has a consistent appearance and structure. However, the types of content included in the documentation differs from API to API. To facilitate understanding, API documentation can include description of classes and methods in the API as well as "typical usage scenarios, code snippets, design rationales, performance discussions, and contracts", but implementation details of the API services themselves are usually omitted. Restrictions and limitations on how the API can be used are also covered by the documentation. For example, documentation for an API function could note that its parameters cannot be null, or that the function itself is not thread safe. Because API documentation is so comprehensive, it can be difficult for the writers to keep the documentation updated and for the users to read it carefully, potentially resulting in bugs. 212 Words
API documentation can be enriched with metadata information like Java annotations. This metadata can be used by the compiler, tools, and by the run-time environment to implement custom behaviors or custom handling. 32 Words
In 2010, Oracle Corporation sued Google for having distributed a new implementation of Java embedded in the Android operating system. Google had not acquired any permission to reproduce the Java API, although a similar permission had been given to the OpenJDK project. Judge William Alsup ruled in the Oracle v. Google case that APIs cannot be copyrighted in the U.S, and that a victory for Oracle would have widely expanded copyright protection and allowed the copyrighting of simple software commands: 80 Words
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