What exactly is the meaning of an API

Question

I ve searched for the definition of an API in a programming language and I am still finding it hard to understand   Could anyone advice me in simple  layman s terms    What is an API  How is it used  When and where is it used

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Searches should include Wikipedia  which is surprisingly good for a number of programming concepts terms such as Application Programming Interface   What is an API           An application programming interface  API  is a particular set of rules   code   and specifications that software programs can follow to communicate with each other  It serves as an interface between different software programs and facilitates their interaction  similar to the way the user interface facilitates interaction between humans and computers       How is it used   The same way any set of rules are used   When and where is it used   Depends upon realm and API  naturally  Consider these    The x86  IA-32  Instruction Set  very useful  -  A BIOS interrupt call OpenGL which is often exposed as a C library Core Windows system calls  WinAPI The Classes and Methods in Ruby s core library The Document Object Model exposed by browsers to JavaScript Web services  such as those provided by Facebook s Graph API An implementation of a protocol such as JNI in Java   Happy coding

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1  What is an API   API is a contract  A promise to perform described services when asked in specific ways   2  How is it used   According to the rules specified in the contract  The whole point of an API is to define how it s used   3  When and where is it used   It s used when 2 or more separate systems need to work together to achieve something they can t do alone

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In layman s terms  I ve always said an API is like a translator between two people who speak different languages  In software  data can be consumed or distributed using an API  or translator  so that two different kinds of software can communicate  Good software has a strong translator  API  that follows rules and protocols for security and data cleanliness    I m a Marketer  not a coder  This all might not be quite right  but it s what I ve tried to express for about 10 years now

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Conaider this situation   Mark and Lisa are secretly a couple  and because of age difference they are not allowed to be together  Mark and Lisa meet every night when nobody is watching  They have estabilished their own set of rules how to comunicate when the time comes  He stands in her garden and throws the small rock at her window  Lisa knows that it is time  and responds by waving from the window and opening it afterwards so Mark can climb in  That was example how the API works  The rock is initial request to another end  Another end waves  opens the window which basicaly means  Welcome in      API is almost like human language but for computers

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An API is a set of commands  functions  and protocols which programmers can use when building software for a specific OS or any other software  The API allows programmers to use predefined functions to interact with the operating system  instead of writing them from scratch  All computer operating systems  such as Windows  Unix  and the Mac OS and language such as Java provide an application program interface for programmers   Source

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It is a set of software components that interact with one another  It provides a set of functions  variables  and object classes for the creation of an application  operating system or any other thing

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An API defines the interfaces by which one piece of software communicates with another at the source level  It provides abstraction by providing a standard set of interfaces - usually functions - that one piece of software  typically a higher-level piece  can invoke from another piece of software  usually a lower-level piece     For example  an API might abstract the concept of drawing text on the screen through a family of functions that provide everything needed to draw the text  The API merely defines the interface  the piece of software that actually provides the API is known as the implementation of the API   It is common to call an API a  contract   This is not correct  at least in the legal sense of the term  as an API is not a two-way agreement  The API user  generally  the higher-level software  has zero input into the API and its implementation  It may use the API as-is  or not use it at all  take it or leave it    A real-world example of an API is the interfaces defined by the C standard and implemented by the standard C library  This API defines a family of basic and essential functions  such as memory management and string manipulation routines

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An API is the interface through which you access someone elses code or through which someone else s code accesses yours   In effect the public methods and properties

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Lets say you are developing a game and you want the game user to login their facebook profile to get your profile information  before playing it so how your game is going to access facebook  Now here comes the API Facebook has already written the program API  for you to do it  you have to just use those programs in your game application using Facebook-API you can use their services in your application Here is a good and detailed look on API    http   money howstuffworks com business-communications how-to-leverage-an-api-for-conferencing1 htm

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Well  in addition to all the answers  I am just adding an example   As others said API stands for Application Programming Interface through which softwares can interact with each other  Note  not a human interaction   Where it is used  An example  You are buying an item online through your credit card  You will provide credit card details and press  continue  button  It will tell you whether your information is correct or not  To provide these results  there are lot of things in the background   The application will send your credit card details to a remote application which will validate your information and send the result back to your application  API is used in this scenario   I hope it helps for the beginners who don t understand really what API is   ANOTHER EXAMPLE  Weather application     Without API - Weather application must open weather com site and read the details as a human does    With API - Weather application will send a message to weather com and receive the result and then display it   SOURCE - Various online resources

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API stands for Application Programming Interface  i e  API is the way for an application to interact with certain system application library etc   For example  there are API s for OS  WinAPI   API s for other applications  like databases  and for specific libraries  for example  image processing   etc   APIs are usually developed in a form consumable by a client application  For C C   applications  it a set header files and dynamic static libraries  For Java - set of jars  And so on

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Application program interface  API  is a set of routines  protocols  and tools for building software applications  An API specifies how software components should interact and APIs are used when programming graphical user interface  GUI  components  A good API makes it easier to develop a program by providing all the building blocks  A programmer then puts the blocks together   source  http   www webopedia com TERM A API html

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an API Application Programming Interface  is a set of defined functions and methods for interfacing with the underlying operating system or another program or service running on the computer  It is usually used by establishing a reference to a library in your software or importing a function from a dll  It is used in one form or another in almost all software  being explicitly called in your program or implicitly called by the compiler

[api] What exactly is the meaning of an API?

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