java - 实现 java Comparable 类的问题

Question

下图显示了在尝试实现位于我的 Tool 中的 compareTo() 方法时涉及 if-else 条件的编译错误类(class)。我不确定这个问题，因为该方法似乎是 public 并且在我的 Tool 类中(从中构造被比较的两个对象)。

public interface Product {
    public abstract String getName();
    public abstract double getCost();
}

public abstract class Vehicle implements Product {
    private String name;
    private double cost;

    public Vehicle(String name, double cost) {
        this.name = name;
        this.cost = cost;
    }

    public String getName() {
        return name;
    }

    public double getCost() {
        return cost;
    }
}

public class Car extends Vehicle {
    public Car(String s, double d) {
        super(s, d);
    }
}

public class Truck extends Vehicle {
    public Truck(String s, double d) {
        super(s, d);
    }
}

public class Tool implements Product, Comparable<Product> {
    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(Product obj) {
        if (getCost() < obj.getCost()) {
            return -1;
        } else if (getCost() == obj.getCost()) {
            return 0;
        } else {
            return 1;
        }
    }
}

import java.util.*;
public class InventoryDemo
{
    public static void main(String [] args) {
        ArrayList<Product> list = new ArrayList<Product>();
        list.add(new Car("Jagur", 1000000));
        list.add(new Car("Neon", 17000));
        list.add(new Tool("JigSaw", 149.18));
        list.add(new Car("Jaguar", 110000));
        list.add(new Car("Neon", 17500));
        list.add(new Car("Neon", 17875.32));
        list.add(new Truck("RAM", 35700));
        list.add(new Tool("CircularSaw", 200));
        list.add(new Tool("CircularSaw", 150));
        list.add(new Tool("saw1", 200));
        list.add(new Tool("saw2", 150));

        if(list.get(9).compareTo(list.get(10)) == 0) {
            System.out.println("\nThey are the same size using compareTo().");
        } else {
            System.out.println("\nThey are not the same size using compareTo().");
        }
    }
}

Answer 1

问题是您的列表类型为List<Product> ，但产品未实现Comparable接口(interface)，因此该类型不实现该方法。

制作

public interface Product extends Comparable<Product> {
    public abstract String getName();
    public abstract double getCost();
}