从一个类中调用一个方法，该类是我的ArrayList的一个类的子类

Question

I had attached the code in the end.

So i have a class called Product, ComputerPart and Ram. Ram extends Computer part , ComputerPart extends product from which all classes override price attribute since Product is an abstract class.

Is my implementation of an ArrayList vs a List correct ? How do i reach a getter method in the ComputerParts class via the arraylist. I am a little confused on when i pass 76f though ComputerPart , how is it usable since it has not been properly instanciated

abstract class Product {
    protected float price;
    public static int i =0;                   // to keep count starts at zero 
    protected static int ID ;               // to update and keep track of ID even if i changes 

     // return the price of a particular product
    abstract float price();
}


class ComputerPart extends Product {

     public ComputerPart(float p) {
        i += 1;                             // each time constructor invoked ,  
        ID = i ;                                // to update ID even if i changes.    
        price = p;
    }

    public float price() { return price; }

    public static String getID(){   // a getter method so ID can be nicely formated and returned
        String Identification =  "ID#" + ID;
        return Identification;
    }
}

public abstract class GenericOrder {

    public static void main(String[] args) {

        ArrayList<Product> genericOrder= new ArrayList<Product>();
        genericOrder.add(new ComputerPart(76f));
    }
}

Answer 1

ArrayList<Product> genericOrder= new ArrayList<Product>();

This is fine, though it is better practice to declare the variable type as the List interface (which makes your code more modular, since you can easily switch to a different List implementation) :

List<Product> genericOrder= new ArrayList<Product>();

As for accessing specific properties of the objects stored in the list :

You can fetch the Product from the list :

Product p = genericOrder.get(0);

Then you can check if it's a ComputerPart and cast it in order to access the specific methods of ComputerPart :

if (p instanceof ComputerPart) {
    ComputerPart c = (ComputerPart) p;
    System.out.prinln(c.price());
}