Can't find symbol (method) which is defined in an object's class

Question

This here is the code for a class that modelizes a catalog for a computer parts shop using an ArrayList. All the included objects (products) have been defined, including methods for getting and setting a quantity variable.

import java.util.*;

public class AvailablesCatalog {

public AvailablesCatalog(List cat1) {

    Motherboard item1 = new Motherboard("MD4652", 1995, "Lenovo", 100.50,  "Intel", 32, 5, 0);
    CPU item2 = new CPU("RTJ357", 1850, "Intel", 182.50, 2.9, 6, 0);
    Graphics item3 = new Graphics("P99E0", 2014, "AMD", 70.50, "AMD", 6, 0);
    RAM item4 = new RAM("THN46", 1999, "Microsoft", 30.50, "DDR2", 4, 1600, 0);
    HD item5 = new HD("M9052", 2001, "LG", 100, "SSD", 2.5, 750, 0);
    Monitor item6 = new Monitor("D42", 2006, "LG", 200, "LED", 17.5, "1920x1080", "HDMI", 0);
    Keyboard item7 = new Keyboard("F16", 2010, "Microsoft", 25.70, "Wireless", 0);
    Mouse item8 = new Mouse("JERRY", 2010, "Microsoft", 30.50, "Laser", "Wireless", 0);
    Printer item9 = new Printer("PRNTR", 1995, "Lexmark", 40.50, "Laser", "Colored", 0);

    cat1.add(item1);    
    cat1.add(item2);   
    cat1.add(item3);   
    cat1.add(item4);
    cat1.add(item5);
    cat1.add(item6);   
    cat1.add(item7);   
    cat1.add(item8);
    cat1.add(item9);

}

public String toString(List cat1) {
    int flag = 0;
    for(int i=0; i<cat1.size(); i++) {
        if(cat1.get(i).getQuantity() != 0) {
            System.out.println(cat1.get(i).toString());
        }
        else {
            flag ++;
        }
    }
    if(flag == 9) {
        System.out.println("No products");
    }
    return "-------------------------------------------------------------------------";
}

}

As you can see, i'm trying to use the getQuantity() method in the AvailablesCatalog class. The problem is that when i try to compile i get a cannot find symbol error for the getQuantity method. Does that mean that i actually need to define the method in the catalog's class as well? In which case, how do i make it return each different product's quantity? Thanks in advance.

EDIT: since i didn't make that clear, all the product objects have a common Product superclass. Then, should i change toString(List cat1)

to

toString(List<Product> cat1)

?

EDIT 2: That was indeed the case after all, the only prblem was being that i was defining getQuantity() in all of my products, instead of the base class (Product) Once again, thanks everyone.

Answer 1

You are not using a genericized List, so when you call get(i) on it, it returns an Object, and there is no getQuantity() method on Object. Try declaring your List as a List<Category> or whatever your base class for RAM, Motherboard, Keyboard etc is.

Answer 2

because compiler doesn't know that your objects in List would be of type Catalog

change

List cat1

to

List<Catalog> cat1

in toString()

Assumming Catalog is your class containing this method and you have strictly all objects of this type in list

Answer 3

First of all, we do not understand what items you're adding to the list. What are the superclass of Motherboard, Graphics, CPU, Monitor, Keyboard, Mouse, etc.?

Since you're using a generic List without specifying a type, it is seen as a raw type and thus, the items in the list are implicitly an Object and Object doesn't have a getQuantity() method.

A solution will be to create an Item abstract, Serialized class that all the relevant subclass must inherit, i.e., Keyboard, Mouse, Motherboard, etc., and a List of these Items, i.e., List<Item> cat1.

Then your toString will have the following method signature:

public String toString(List<? extends Item> cat1)

I hope this helps.

Answer 4

You could use Product as a generic wildcard argument

public String toString(List<? extends Product> categoryList) {