How vital is me knowing casting ?? can i move on ?

In my programming career I've used casting from time to time. It's not used every day, but sometimes it helps.

Let me try to explain this in a different way:

Now, let's say that you have a class that processes Products, and there's a method there (processProducts()) with a signature that you cannot modify, meaning the method needs to accept an array of Products, and you cannot modify it to accept an array of AppleTV.

when you implement that method, it gives you a list of Product type inside it. Even if you KNOW that you are sending a list of AppleTV, and the code will compile because AppleTV inherits from Product, inside that method you will only have a list of Product instances, so you can only call manufacturer() on them.

What if you NEED to call appleTVName() or iPhoneName() on them, but calling those methods on Product gives you an error? You cast those instances to the type you need

See my code below. Keep in mind this is not the best optimized code, but it's here to explain the concept.

class Product {
    public String manufacturer() {
        return "Apple";
    }
}

class iPhone extends Product {
    public String iPhoneName() {
        return "iPhone X";
    }
}

class AppleTV extends Product {
    public String appleTVName() {
        return "Apple TV 4K";
    }
}

public class BatchProcessingJob {
    public static void processProducts(Product[] products) {
        //Hmm, we only get Product[] here, but I'm sure I'm sending AppleTV[] to this method (see below)
        //let's get the first product from the list:
        Product p = products[0];
        p.manufacturer(); //this works!
        p.appleTVName(); //this fails!

        //we need to CAST the product to the correct type
        if (p instanceof AppleTV) { //doesn't hurt to check the type
            AppleTV atv = (AppleTV)p;
            atv.appleTVName(); //now we can call it!
        }
    }
}

AppleTV tv1 = new AppleTV();
AppleTV tv2 = new AppleTV();

AppleTV[] appleTVList = new AppleTV[]{tv1, tv2};