How do I access a static variable of a subclass through a for loop.

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Hi!

I have a superclass called product and 3 subclasses called Laptop, Web and Microphone. In each subclass a created a static variable that counts the number of products from each class. I created an Array list that shows the products from each but my problem is that a don't know how to call the static variable assigned to each object.

What I have tried:

The page of subclass laptop:

Java

public class laptop extends Products {
     static int stock=0;
    public laptop(String name, String color, Double price, Double discount) {
        super(name, color, price, discount);
        stock++;

 public static int getStock() {
        return stock;
    }
    }

The class of the Array List that creates the objects:

Java

<pre>ArrayList <Products> catalog = new ArrayList<>();
        catalog.add( new web("web", "red", 145.0, 1.0));
        catalog.add( new microphone("microphone", "red", 145.0, 1.0));
        catalog.add( new laptop("laptop", "red", 145.0, 1.0));

So, If I would call web.getStock everything works fine and I can access the stock. But if I want to display the list using a for loop I don't really know how to access the stock of each product.

Java

<pre>   for(int i=0; i<catalog.size(); i++){
           System.out.println(catalog.get(i).name + " " + (Here! I don't know how to acces the static variable of each catalog.get(i).name);

Posted 5-Jun-18 21:52pm

Member 11018842

Updated 6-Jun-18 10:43am

v2

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2 solutions

Solution 1

Why not use separate lists for each product type, so you can just use ArrayList.size()[^] to get the count?

Posted 6-Jun-18 0:55am

Richard MacCutchan

Comments

Member 11018842 6-Jun-18 16:28pm

Because I want to create a database for a lot of products, so my code would be very complicated if I would create lists for let's say 100 different products.

Richard MacCutchan 6-Jun-18 17:07pm

That does not make sense. If you are using a database then you are unlikely to need such a list.

Member 11018842 6-Jun-18 17:22pm

I expressed myself wrong. I just want to say that if I would have 100 of different products the code will be very complicated.

Richard MacCutchan 7-Jun-18 3:40am

Not if you do it right.

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CPallini · Accepted Answer · 2018-06-06T10:44:00

Solution 3

Define an abstract method in the Product class and override it in the derived ones. For instance

Java

abstract class Product
{
  String name;
  public Product(String name)
  {
    this.name = name;
  }
  public abstract int getStock();
}

class Laptop extends Product
{
  static int stock = 0;
  public Laptop(String name)
  {
    super(name);
    ++stock;
  }
  @Override
  public int getStock()
  {
    return stock;
  }
}
 //...
 // in main method
    ArrayList <Product> catalog = new ArrayList<Product>();
    catalog.add( new Laptop("foo") );
    catalog.add( new Laptop("goo"));
    System.out.println( catalog.get(1).getStock() );

Posted 6-Jun-18 10:44am

CPallini

Comments

Member 11018842 6-Jun-18 19:56pm

It worked. Thank you very much.

CPallini 7-Jun-18 4:20am

Did you doubt about? :-D
You are welcome.

Member 11018842 7-Jun-18 4:58am

If I would have, let's say 5 types of laptops, how can I keep the evidence of the stocks for each of them? Should I create public classes for each kind of laptop or just to create static variables(for each kind of laptop) in the class Laptop? How is used in practice?

CPallini 7-Jun-18 5:29am

You should make different classes if you need them (e.g. different states or behaviours). Don't make different classes just to differentiate their instances counts.