java - 无法创建抽象父类(super class)的非抽象子类？

Question

我有一个子类，它声明了我的抽象父类(super class)中的所有方法，但它仍然给我一个错误，指出我的类不是抽象的。我不明白为什么会抛出这个错误。

我收到的具体错误是

PhoneBookEntry.java:1: error: PhoneBookEntry is not abstract and does not override abstract method compareTo(Object) in Comparable

我的问题代码:

public abstract class PhoneNumber implements Comparable
{
   protected String firstName, lastName;
   protected int number;

   public PhoneNumber(String firstName, String lastName, int number)
   {
      this.firstName = firstName;
      this.lastName = lastName;
      this.number = number;
   }

   public abstract String getLastName();
   public abstract String getFirstName();
   public abstract int getNumber();

   public int compareTo(PhoneNumber other)
   {
      int last = other.lastName.compareTo(lastName);
      int first = other.firstName.compareTo(firstName);
      int num = other.number - number;
      if(last > 0)
         return 1;
      else if(last < 0)
         return -1;
      else
         if(first > 0)
            return 1;
         else if(first < 0)
            return -1;
         else
            if(num > 0)
               return 1;
            else if(num < 0)
               return -1;
            else 
               return 0;
   }
}

还有我的子类:

public class PhoneBookEntry extends PhoneNumber
{
   public PhoneBookEntry(String firstName, String lastName, int number)
   {
      super(firstName, lastName, number);
   }

    public String getLastName()
   {
      return lastName;
   }
   public String getFirstName()
   {
      return firstName;
   }
   public int getNumber()
   {
      return number;
   }

   public int compareTo(PhoneNumber other)
   {
      super.compareTo(other);
   }

}

Answer 1

这就是问题:

public int compareTo(PhoneNumber other)
{
   super.compareTo(other);
}

您已指定您只是实现原始类型 Comparable，该类型的方法签名为:

int compareTo(Object)

最干净的解决方法是将 PhoneNumber 的声明更改为:

public abstract class PhoneNumber implements Comparable<PhoneNumber>

您可以实现compareTo(Object)，但是您真的希望能够将电话号码与任何其他对象进行比较吗？仅仅声称能够将电话号码与其他电话号码进行比较更有意义(IMO)。