Help with understand what the "Java API" is

[stark skiff]

I've come across the term "Java API" online but didn't understand what that actually means. I've tried googling to understand what it means but couldn't understand it. I'd really appreciate it if someone could help me understand what it means. Thanks :)

[brisk snow]

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[stark skiff]

Please ping me when you're replying

[shell python]

an "interface" is a layer of operations that separate systems can use to interactwith each other. this layer defines the available operations without defining how to do those operations.

for example, a UI, a user interface, is used for a user to interact with a system, and the user doesn't have to see the code behind each button, they just see the button and probably text saying what that button does.

API is short for "application programming interface", it's used to let 2 programs or parts of programs interact with each other. for example, web apis define interfaces for programs to interact with websites.

apis also exist directly in code. libraries are also considered separate parts of a program, so libraries also define interfaces so other code can interact with the library. these are also apis, since they let different parts of a program interact with each other.

amongst the libraries are the standard libraries, which define basic operations in each language. for java, that's java.lang, java.util, etc. these are the "Java APIs", the apis that java defines for developers to use.

(last part was hastily written so might have some inaccuracies, if anyone spots any please do correct me)

[stark skiff]

Why call it API though? Why not just the Java library/inbuilt packages? (I come from a little bit of experience in C++. So it'll be helpful if you can point out the differences)

Is it the same thing? or are there any differences between libraries and APIs

[shell python]

"API" refers just to the interfaces without really worrying about the implementations. you can call them the java standard libraries just as well

[stark skiff]

but isn't that what libraries do as well? We only use the librarires and the features that it provides without having to worry about internal details

[shell python]

libraries define an api. you call the api at developing, only the language truly invokes the implementations at runtime

"library" as broader than api, it refers to the whole thing

think of it like the difference between .h and .c files

.h is the thing defining the interfaces

when you write code, you're only using the .h files

when you compile, the compiler obtains the .c files, and the runtime then uses the .c files

[stark skiff]

We write custom header (created by the user) with .h extension and the actual C programs with .c extension

[shell python]

(or .cpp i guess)

[shell python]

right, and what does #include use? just the headers. it only cares about the headers at that moment.

[stark skiff]

Yea I got what you're saying. In .h files, we define the class and provide the interface (without any implementation details) so that people can look at that .h file and figure out what functions they can use. We then define the functions/methods in the .cpp file. We only include the .h files in the main.cpp file and the linker will take care of finding that implementation from the .cpp file that we wrote earlier. This is how we abstract the implementation details from the class definition (while providing the interface)

[shell python]

the compiler and runtime care about the implementation, while the development environment doesn't

[stark skiff]

wait a sec. I think I kinda understood

let me explain what I understood and then tell me if I understood it correctly

Basically, all the .h files that we write the interfaces in, are included in what's called the "API" and the library consists of all the .h and .cpp files where the classes are declared in .h files and defined in .cpp files. In other words, all the interfaces to using inbuilt features come under the term "API" and the interfaces + implementation combined comes under the library. Is that right?

@shell python did I misunderstand something?

[shell python]

yeah that's right

[stark skiff]

alright got it. Thanks a lot!!

[brisk snow]

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