Abstract classes

[bigapewhat]

I have this problem that this is my second semester in programming and i have assignments like this which i cannot understand since the teacher in Poland do not explain very well. i understand the usage of abstract classes, how they can be used and for what reasons, but what i dont understand in this example is how to (reference to the current user, or making a command like kate.buys(carrot))
i just need some help understanding this material

Problem 1.4 Write a set of classes representing shopping in a supermarket.

* Purchase: name of product, unit price, quantity.
* Cart: contains a list (collection) of products put into this cart, reference to the current user (object of class Customer) etc.
* Customer: name, reference to the currently used cart, list of bills (objects of class Bill) for purchases already completed and paid. Customer having a cart can put products into the cart (kate.buys(carrot)) and pay for all products at
checkout (object of class CheckOut) receiving the Bill.
*CheckOut: remembers customers who already have paid (kate.pays(checkout) and/or checkout.checksOut(kate) and their bills (which are also rememered by Customers). CheckOut can be asked for a report (object of class Report).
* Bill: represents bill with customers's name, date, list of products, amount paid etc.
* Report: report of checkout with list of bills paid at this checkout.
_______________________________________________________________________________

public abstract class Purchase {
	
	
	public abstract String getNameOfProduct();
	public abstract int getUnitPrice();
	public abstract int setQuantity(int a);
}

 
public class Bread extends Purchase{
	int amount = 0;
	
	@Override
	public String getNameOfProduct() {
		return "Bread";
	}

	@Override
	public int getUnitPrice() {
		return 3 * amount;
	}

	@Override
	public int setQuantity(int a) {
		return amount += a;
	}
	
	public int getQuantity(){
		return amount;
	}
}

import java.util.*;
public class Cart{
	List<String> sCart = new ArrayList<String>();

	public void addItem(String item){
		sCart.add(item);
	}
	
}

public abstract class Customer{
	String name;

	public void setName(String n){ 
		name = n;
	}
	
	public String getName(){
		return name;
	}
}

[tfityo]

This is C++ forum, not a java one.
In C++ if some class is abstract you cannot use object of this class.
You should develop also inherited non-abstract class and then you can create objects of this new non-abstract class. I suppose that everything is similar in java.

[bigapewhat]

my bad, how do i remove post