java - 我不断收到“无法找到符号方法compareTo”错误

Question

我希望我的程序比较两个对象，但我不断收到错误消息“找不到符号方法compareTo(Product)”。但我已经检查过，并且确实在 Tool 类中定义了 CompareTo 方法，如下所示。

public class InventoryDemo
{
   public static List<Product> products = new ArrayList<Product>();
   public static void main(String [] args)
   {

    products.add(new Car("Jaguar", 1000000.00));
    products.add(new Car("Neon", 17000.00));
    products.add(new Tool("JigSaw", 149.18));
    products.add(new Car("Jaguar", 110000.00));
    products.add(new Car("Neon", 17500.00));
    products.add(new Car("Neon", 17875.32));
    products.add(new Truck("RAM",  35700.00));
    products.add(new Tool("CircularSaw", 200.00));
    products.add(new Tool("CircularSaw", 150.00));


    InventoryDemo.takeInventory("CircularSaw");
    if(products.get(7).compareTo(products.get(8)) == 0)
    {
        System.out.println("The price of Saw1 and the price of Saw2 are the same.");

    }
    else if(products.get(7).compareTo(products.get(8)) == 1)
    {
       System.out.println("Saw1 is more expensive tham Saw2.");
    }
    else
    {
        System.out.println("Saw2 is more expensive tham Saw1.");
    }


}

public class Tool implements Product, Comparable<Tool>
{

private String name;
private double cost;

public Tool(String name, double cost)
{
    this.name = name;
    this.cost = cost;
}
public String getName()
{
    return name;
}
public double getCost()
{
    return cost;
}
public int compareTo(Tool t)
{
    if(cost > t.cost)
    {
        return 1;
    }
    else if(cost == t.cost)
    {
        return 0;
    }
    else 
    {
        return -1;
    }
}
}

Answer 1

这可能是因为您将实例保存在接口(interface)支架中，而接口(interface)没有任何有关它的信息。