#65 What is Interface in Java

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In this lecture we will learn:
What is an interface in java?
Use of interface
implements keyword in an interface
Variables in an interface
#1
Interface:-
In an abstract class, we can have both abstract methods as well as normal or concrete methods.
If your class has only abstract methods then instead of using class, you can simply use an interface in place of it.
Interface is not any class.
Every method in an interface is public and abstract by default.
Even if you do not use two keywords (public and abstract) with methods then also it will not give an error in an interface. By default, it will consider all methods as public and abstract.
We cannot instantiate an interface.
Interface only shows the design and it does not provide any implementation.
To provide an implementation of methods, you need to create a class and instantiate it also.
e.g,
interface A
{
methods()----
}
#2
implements keyword:-
To implement an interface, we use the keyword - implements.
If you use the implements keyword with class, then it is compulsory to give an implementation of all the methods that are defined in an interface.
If you do not give an implementation of all methods then it will make your class an abstract class by default.
So, to make a concrete class, you have to give the implementation of all methods present in an interface.
e.g.,
class B implements A
{
methods() {
statement;
}
------
}
#3
Variables in an interface:-
We can call the methods of an interface by creating an object of the class that implements an interface.
We can also declare variables in an interface.
All the variables in an interface are final and static by default.
So, we first have to initialize the variables in an interface.
As a variable is static in an interface, then you do not need to create an object for it. You can directly call the variable by using the interface name.
e.g., A.area; (here, area is a variable initialized in an interface)
As the variable is final, you can not change the value of that variable after initializing it once.
-Interface does not have its own memory in the heap.
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[@DeeperRed-of1gp]

At 7:26 it is said that "we are doing implement not extends so only methods are available and variables are not available". Actually, regardless of what we do implementation of interface or extends of parent class, the variables also gets passed on in child. When we do Subclass obj = new Subclass(); we can see that variables are accessible. The thing with interface is that as the variables are final, so we can't change it. But it is available in child class! Maybe it was just Slip of tongue by Telusko! Enjoying the series so much! Thank you for posting it!❤

[@DeeperRed-of1gp]

Actually according to GPT , In Java, static fields declared in interfaces are accessible through the implementing class, not inherited. When we access B.age in above example in main method, it's not due to inheritance, but rather because interface fields are implicitly public, static, and final. In our case, age is a static field of the A interface, which means it can be accessed using the interface name itself (A.age) or through any class that implements the interface (B.age). So, while it may seem like the field is inherited, it's actually being accessed through the interface. This behavior allows for constants and other shared data to be accessed consistently through the interface, regardless of the implementing class.

[@thusith-tec307]

Today I subscribed you after watching this video. Your explanation and English pronouncing are better than others. I respect you my new Teacher ❤. Love from Sri Lanka

[@jibonjibon8231]

Your Process of explaining and the step by step developed example is just blowing my minds. Tomorrow is my java final exam. I have regrate that why I didn't follow you from before! Your teaching system is well pre-planed, clear. I have a request, plz don't stop making tutorial. Keep doing by this way of explaining. Need Python ,framework, Algorithm from you.

[@ramyapinapothu9901]

Amezing explination everyone saying only theory u are the only one following practical manner ur having great explanation

[@obaldalmeida6308]

I have been watching Navin sirs old vedios and found this gem ....good to know you are doing well....looking fresh sir ✨ with an upgrade

[@daulitech219]

I read Interface through a book but I couldn't understand it, until I found your video. Thanks

[@projyoti7489]

What a type of teaching skills ! Mind-blowing

[@Arsun-77]

Me videos lo examples tho concept inka baga ardm aythundi anna...❤

[@AmarGrg]

Hi @Telusko thank you very much for all those wonderful videos. Just started learning java and I am already learning alot. Have a quick question for you, while doing PHP we used to write interfaces for the model entity class, what do you think about it? what might be the pros and cons?

[@iqbalsingh3848]

your video just blow my mind.. its crazy ... thanks for a lot of information...

[@naveenagrawal2298]

thanks for these tutorials . these all are really cool

[@rajeshwarijindam-dx3xz]

Anna mi teaching baa super undhi

[@adityasrinivas3069]

Video #66. and #65 should be interchanged, i.e, explain what is an interface and then explain why it is important. It will be easier to understand.

[@Telusko]

Thanks for the correction

[@sriemandi3978]

Merry Christmas Naveen bro

[@alwinvj6487]

Thanks for this video🤗

[@manas332]

Excellent explanation

[@roshanekka8293]

nice explanation

[@mangaraj45]

That's not my age 💀🌚😅

[@mohitx3g]

Bro's age is 43, and he written 44 😂

[@Programing-lo3og]

Thanks You Sir

[@Hemanth83439]

kollada mona 👌

[@nila-333]

Thank you so much

[@ajayghode3602]

when we create interface. In interface all methods are 'public abstract' by default. So, no need to write public abstract. we need to define those methods in the class. Otherwise that class will become abstract. Again we need to creat concrete class and define methods. In the interface, we can decleare varibles but those variable will be final and static. So, we have to define those variables like int age=32; String area="Mumbai". Interface don't have memories in the heap. we are doing implements(class implements interface) so we implements only methods NOT variables. As interface don't have memory how can we create non-final or non-static variables in the main class so, we can not be able to change variables ' values.

[@chouaibakni2828]

Thanks

[@raghavsood768]

Notes: All variables inside interface are static and final

[@mohamedmurshid9794]

and public by default too. all the methods inside interface are public and abstract.

[@mehakfatima6531]

​@@mohamedmurshid9794 well they have to be public so that the abstract methods inside it can be used further in derived classes or the whole point of creating a interface will be nothing

[@mohamedmurshid9794]

@@mehakfatima6531 yep true. But i just added those are public too. Not only static and final. Thank you for this comment.🤗

[@Nothingtosaymore]

Thank you

[@Ambitious675]

Thank you so much sir :)

[@adityamishra_11]

Are we take scanner (input) at the time of declaring any variables inside the interface.?

[@adityamishra_11]

@Telusko.

[@VishnuSai-u2e]

Without out main() we can i print any statement?

[@109abdulakram3]

hello sir,u told that class b implements class a only methods ...but i can acess B.name its is showing the variable name

[@naveenagrawal2298]

what does you ment by saying you dont get access to variables in implements . As I tried on my own we get access to interface variables in subclasses, but there are just staic final and public.

[@srimantamondal8769]

Can someone tell me why inside println(), "x:" is used. This variable "x" is not declared anywhere and is not giving any error. Also if it is not a variable then let me know what it is.

[@santhosh-benz7]

Here inside the println(), "x:" is used , it is provided by the IDE ( here VS code ) , which means it remains you to code here or pass the parameter , which makes you aware about the line of code . It needs some thing based on the code . I think you can Understand 😅

[@shubhrajit2117]

You can disable it by going to settings -> Java hints -> None

[@filmbuzz9419]

Can i implement another method in class B

[@rohitgundam2275]

How is he able to create an object A (since this has the same name as the interface?)

[@DSASimplified-zs6ll]

Bro They have defined the object "obj" with type A which is class name Which is implemented by interface

[@hirenkansara77]

👌👌👌👌👌

[@sushmithakn6003]

Why this error come - failed to resolve main method code lens :inter faceis not a valid java identifier

[@sheikhnasir3437]

6:13 Funniest part 😂

[@TochukwuVictor-qe4xd]

❤❤

[@AbuIshaqAlShafii]

5:12

[@JulieJulie-x6t]

🎉❤

[@Hawkai-ro2hx]

That's not my age was personal

[@abhi._77]

Nipora