java - 不兼容的类型 : Cannont be converted

Question

所以我创建了三个类； PetStore、宠物和鸟类。 PetStore 类是主类，pet 扩展 PetStore，然后 Bird 扩展自 Pet

现在我使用以下代码创建了一个驱动程序类。

public class Main{
     public static void main(String[] args){
         //create a pet objects
         Bird macaw = new Bird("hyacinth macaw", 300.99, 48.0);

         //create a pet store
         PetStore happyPetsInc = new PetStore();

         //add the pets to the pet store
         happyPetsInc.addPet(macaw);

我正在尝试将鸟对象添加到 PetStore 中的数组列表中。

我收到错误:“不兼容的类型:Bird 无法转换为 java.lang.String”

有人标记了这一点并说要发布 PetStore 和 Bird 类，所以这里是:

public class PetStore
{
    //varibles
    String pet;

    //ArrayList
    ArrayList<String> Pets = new ArrayList<String>();

    //constructor
    public PetStore(){

    }

    /**
     * add the paramameter to the ArrayList
     * @param pet
     * @return void
     */
    public void addPet(String pet){
        Pets.add(pet);
    }

    /**
     * removes the paramater to the ArrayList
     * @param pet
     * @return true(success) false(failure)
     */
    public boolean sellPet(String pet){
        this.pet = pet;
        if (Pets.contains(pet)){
            Pets.remove(pet);
            return true;
        }else{
            return false;
        }
    }

    /**
     * counts the number of elements in the ArrayList
     * @param none
     * @return int, the number of the elements in Pets
     */
    public int getInventoryCount(){
        return Pets.size();
    }

    /**
     * displays information about the pets in the ArrayList
     * @param none
     * @return void
     */
    public String toString(){
        for (int i = 0; i < Pets.size(); i++){
            System.out.println("Pet #" + (i + 1));
            String index = Pets.get(i);
            return index.toString();
        }
        return "\n";
    }
}
public class Bird extends Pet
{
    //varibale
    double wingspan;
    //constuctor
    public Bird(String species, double cost, double wingspan){
        super(species, cost);
        this.wingspan = wingspan;
    }

    /**
     * Sets the wingspan of the bird
     * @param wingspan
     * @return none
     */
    public void setWingspan(double wingspan){
        this.wingspan = wingspan;
    }

    /**
     * Gets the wingspan of the bird
     * @param none
     * @return double
     */
    public double getWingspan(){
        return this.wingspan;
    }

    /**
     * Displays strings describing the bird
     * @param none
     * @return String
     */
    public String toString(){
        return "Species: " + species + "\nCost: $" + cost + "\nBird (Wingspan: " + wingspan + " inches)";
    }
}

Answer 1

面向对象编程的思想是，用类和类的实例(对象)来表示现实生活中的对象。因此，PetStore 是关于宠物的，而不是字符串。所以这样做:

在 PetStore 中替换

ArrayList<String> Pets ...
addPet(String pet)...
sellPet(String pet)...

与

ArrayList<Pet> Pets
addPet(Pet pet)
sellPet(Pet pet)

另外，在 PetStore.toString() 中替换

String index = Pets.get(i);

与

Pet index = Pets.get(i);