package bookstore.model.eneity;import java.util.*;import java.io.Serializable;import java.lang.Math;public class Cart implements Serializable{	private HashMap items;	private double cost;			public Cart() {			}	public void addItem(Product Product,int number) {		}	public void modifyNumberByProductId(Integer productId,int number){			}	public void deleteItemByProductId(Integer productId){			}	public void deleteItemsByProductId(Integer[] productId){			}	public void clear(){			}		public void getCartItem(){			}		public HashMap getItemNumber(){				return items;			}	public boolean isEmpty(){				return true;	}	}