如何通过for循环访问子类的静态变量。 [英] How do I access a static variable of a subclass through a for loop.

问题描述

嗨！



我有一个名为product的超类和3个子类，叫做Laptop，Web和Microphone。在每个子类中，创建了一个静态变量，用于计算每个类的产品数量。我创建了一个数组列表，显示每个产品，但我的问题是，不知道如何调用分配给每个对象的静态变量。



我尝试过：



子类笔记本电脑的页面：

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:

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;
    }
    }

创建对象的数组列表的类：

The class of the Array List that creates the objects:

<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));

所以，如果我打电话给web.getStock，一切正常，我可以访问股票。但是，如果我想使用for循环显示列表，我真的不知道如何访问每个产品的库存。

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.

<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);

推荐答案

为什么不为每种产品类型使用单独的列表，因此您只需使用 ArrayList.size（） [ ^ ]获取计数？

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

在 Product 类中定义一个抽象方法，并在派生的方法中覆盖它。例如

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

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() );

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