如何重写compareTo（）。 如果它是可能的

Question

public int compareTo(Object obj){
   Books bk = (Books) bk;
   return this.id - obj.id;
}

my code works fine when id is an Integer and when is a positive value. Is it possible for id to be a negative value? How to change the code for that?

Answer 1

The following is perhaps the easiest way to implement it:

public int compareTo(Object obj) {
   Books bk = (Books)obj;
   return Integer.compare(this.id, bk.id);
}

Your current version is almost correct, except that it is susceptible to integer overflow.

Answer 2

When you override compareTo you get to define the answer to these questions. It completely depends on your program whether it's possible for id to be a negative value. The question you have to ask yourself is "what does it mean for one book to be 'larger' (or smaller) than another one?". If the answer is just which ever has the larger id is a larger Book, then your implementation is fine, except for one minor mistake:

public int compareTo(Object obj){
   Books bk = (Books) obj;
   return this.id - bk.id;
}

Answer 3

You must be able to return a negative value. From the Comparable specification, if

a.compareTo(b) > 0

then

b.compareTo(a) < 0

Otherwise you could not use compareTo() to stablish an order

Answer 4

I made it work :D

return (this.id > bk.id ) ? -1: (this.id < bk.id) ? 1:0 ;

this works how I wanted it but thanks for your reply