java - 从不同的构造函数访问和添加数据

Question

我有名为 Item、Store、Customer 的类。

我正在使用LinkedList 来移动类。我没有使用 LinkedList 的经验。几天前才开始。

元素类别

public class Item{
   public Item(Store store, String code, String name){
      this.code = code;
      this.name = name;
   }
   @Override
   public String toString(){
      return name + " : " + code ;
}

商店类

public class Store{
    private LinkedList<Item> items = new LinkedList<Item>();
    public Store(String name, String number){
        this.name = name;
        this.number = number;
    }
   public void addItem(String code, String name){
      items.add(new Item(code, name);
   }
   public void viewItem(){
     for(Item item: items) 
       System.out.println(item);
   }
}

当我只被允许将商品添加到商店时，我不太确定这部分。然后我会将商店添加到客户中。因此，客户可以从商店中进行选择。

Customer

    public class Customer{
        private LinkedList<Store> stores = new LinkedList<Store>();
        public Customer(){
            stores.add(new Store("Game" , "1"));
            stores.add(new Store("Grocery" , "2"));
            // I struggle to add item with addItem method
            stores.get(0).addItem("001A" , "GTA");
            //I don't think it's actually way of adding
           //Anyway I think get(0). will add item to '0' index.So I would be the 'Game' store.
           stores.get(0).addItem("001B", "GOD OF WARS");
           stores.get(0).addItem("001C", "THE LAST OF US");

           stores.get(1).addItem("002A", "Sandwich");
           stores.get(1).addItem("002B", "Cup Noodle");
           stores.get(1).addItem("002C", "Ice Cream");
        }
        public static void main(String args[]){
          new Customer().viewItem();
        }
        private void viewItem(){
           for(Store store: stores)
               store.viewItem();
        }
    }

我试图仅使用 Store 类中的 LinkedList 将项目添加到 Customer 类。我试试这个方法。

但是当我在 store 类下尝试这个以查看是否有任何数据时，

for(Item item: items)
    System.out.println(item)

我认为输出会是这样的

   GTA : 001A
   GOD OF WARS : 001B
   THE LAST OF US: 001C

   Sandwich: 002A
   Cup Noodle: 002B
   Ice Cream: 002C

但它什么也没打印出来。

谁能给我解释一下吗？我认为添加或访问数据是错误的。

此外，出于测试目的。你能告诉我如何检查吗？

谢谢。

Answer 1

您需要相应地覆盖 Store 和 Customer 中的 toString，例如如下所示:

import java.util.LinkedList;

class Item {
    private String code, name;

    public Item(String code, String name) {
        this.code = code;
        this.name = name;
    }

    @Override
    public String toString() {
        return name + " : " + code;
    }
}

class Store {
    private LinkedList<Item> items = new LinkedList<Item>();
    private String name, number;

    public Store(String name, String number) {
        this.name = name;
        this.number = number;
    }

    public void addItem(String code, String name) {
        items.add(new Item(code, name));
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Item item : items) {
            sb.append(item.toString()).append(System.lineSeparator());
        }
        return sb.toString();
    }
}

class Customer {
    private LinkedList<Store> stores = new LinkedList<Store>();

    public Customer() {
        stores.add(new Store("Game", "1"));
        stores.add(new Store("Grocery", "2"));

        stores.get(0).addItem("001A", "GTA");
        stores.get(0).addItem("001B", "GOD OF WARS");
        stores.get(0).addItem("001C", "THE LAST OF US");

        stores.get(1).addItem("002A", "Sandwich");
        stores.get(1).addItem("002B", "Cup Noodle");
        stores.get(1).addItem("002C", "Ice Cream");
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Store store : stores) {
            sb.append("Store: ").append(store.getName()).append(System.lineSeparator()).append(store.toString())
                    .append(System.lineSeparator());
        }
        return sb.toString();
    }
}

public class Main {
    public static void main(String[] args) {
        Customer customer = new Customer();
        System.out.println(customer);
    }
}

输出:

Store: Game
GTA : 001A
GOD OF WARS : 001B
THE LAST OF US : 001C

Store: Grocery
Sandwich : 002A
Cup Noodle : 002B
Ice Cream : 002C