What exactly is this functionality of an interface in Solidity?

[software-dev2010]

Hello, I started this course and looks amazing with a lot of useful things. Now I'm at lesson 4 where you explain about the interface AggregatorV3Interface. And I don't understand what you are doing here. I came from Java and I know a little bit of JS. I'm refering at that function:

    function getVersion() public view returns (uint256) {
        AggregatorV3Interface priceFeed = AggregatorV3Interface(0x694AA1769357215DE4FAC081bf1f309aDC325306);
        return priceFeed.version();
    }

So, I don't understand what exactly is this: AggregatorV3Interface(0x694AA1769357215DE4FAC081bf1f309aDC325306), it looks like a constructor, but I know that you can't have constructor in an interface.

And also I don't understand why this priceFeed.version() returns 4. The version() function from AggregatorV3Interface is not implemented. How does it return 4?

I watched some videos about interfaces in Solidity and it seems the same like interfaces in Java. Do you have some videos about interfaces where is explained this functionality?

And I try to modify the interface AggregatorV3Interface, I deleted some methods and I changed the name with AggInt like this:

interface IntForTest {
    function version() external view returns (uint256);
}

And then I modified the getVersion() function like this:

    function getVersion() public view returns (uint256) {
        IntForTest priceFeed = IntForTest(0x694AA1769357215DE4FAC081bf1f309aDC325306);
        return priceFeed.version();
    }

And it still return 4. But if change the name of the function, versionApp() instead of version() then it doesn't work, I get an error.
So, can somebody explain me this functionality of an interface in Solidity? Thank you!

[aaankeet]

@software-dev2010
In Solidity, an interface is a way to define a contract's external-facing functions and their signatures without implementing the actual functionality. It acts as a blueprint for other contracts to follow, specifying the required functions and their input/output parameters.

Interfaces allow contracts to interact with other contracts in a standardized and predictable manner. They define a set of function declarations that other contracts can adhere to when interacting with the contract that implements the interface. This enables contracts to communicate and collaborate effectively.

Here the address is wrapped around the AggregatorV3Interface. Which is the name of the Interface where functions and signautres (not logic inside if) are defined but the actual functionality/logic are defined at the address.

AggregatorV3Interface(0x694AA1769357215DE4FAC081bf1f309aDC325306)

If you change the address it won't work because those functions are not implemented at that address
and if you change any functions name/signature it will also wont work because that function signature doesn't exist on the address

Here priceFeed is the variable of type AggregatorV3Interface & has access to all the functions inside it and the logic is coming from this
0x694AA1769357215DE4FAC081bf1f309aDC325306 address which has implemented the version() function.

you use . to access the functions.
priceFeed.version()

Things to keep in mind

1. You can name Interfaces anything
2. function name and arguments & output should match when interacting with other smart contracts
3. The Smart-Contract you are interacting with must have implemented those functions.

Hope this makes sense

[software-dev2010]

Thank you @aaankeet, now I understand