When do we typecast an ethereum address to a contract name ? Also, what is the purpose of the same?

Question

I have been learning and working on Solidity for quite a while now. One thing that I have seen in many codes but did not understand was typecasting (looks like typecasting to me) of addresses to a contract type. When and why is this required ? A few example use cases with explanation would be really helpful. This is one of the codes that I found -

contract MyContract {
}

contract NewContract {
    MyContract a;

    function setMyContractAddress(address _contractAddress) {
        a = MyContract(_contractAddress);
    }
}

Please explain what is happening in the above code. Thank You for your time.

Answer 1

a = MyContract(_contractAddress); will create a reference to the contract MyContract. Doing so allows you to call public functions of that contract.

Now you can do a.whateverFunctionAHas() which will call the function on the contract at the address.