compareTo：如何返回布尔值？

Question

I am told that compareTo has to return an int...not Boolean.
For example:

Returns

0 if a equal b
-1 if a < b
+1 if a > b

I am slightly confused by that. Any help would be greatly appreciated.

public int compareTo(Cheese anotherCheese)
   throws ClassCastException
   {
       if (!(anotherCheese instanceof Cheese))
            throw new ClassCastException("A Cheese object expected.");

       if(getCheeseType().compareTo(anotherCheese.getCheeseType()))
            return -1;
       else if (getCheeseType().compareTo(anotherCheese.getCheeseType()))
            return 1;
       else
            return cheesePrice > anotherCheese.getCheesePrice();
   }   

When I compile, I get the error messages saying:

incompatible types
if(getCheeseType().compareTo(anotherCheese.getCheeseType()))
incompatible types
else if (getCheeseType().compareTo(anotherCheese.getCheeseType()))
incompatible types
return cheesePrice > anotherCheese.getCheesePrice();

Answer 1

compareTo does indeed return an int , not a boolean . You get those compile errors because of that. Inside an if statement, you must put a boolean .

So instead of

if(getCheeseType().compareTo(anotherCheese.getCheeseType()))

write

if(getCheeseType().compareTo(anotherCheese.getCheeseType()) < 0)

Answer 2

just do

return getCheeseType().compareTo(anotherCheese.getCheeseType());

if you want to also compare by price then do

if(getCheeseType().compareTo(anotherCheese.getCheeseType())!=0)
    return getCheeseType().compareTo(anotherCheese.getCheeseType());
//cheeseTypes are equal
if(cheesePrice < anotherCheese.getCheesePrice())
    return -1;
else if (cheesePrice > anotherCheese.getCheesePrice())
    return 1;
else
    return 0;

Answer 3

   // Order by type.
   int delta = getCheeseType().compareTo(anotherCheese.getCheeseType());
   if (delta != 0) { return delta; }
   // If of the same type, order by price.
   if (cheesePrice < anotherCheese.getCheesePrice()) { return -1; }
   if (cheesePrice > anotherCheese.getCheesePrice()) { return 1; }
   return 0;

Answer 4

Yes compareTo method will return int type, not a boolean . But you are using getCheeseType().compareTo(anotherCheese.getCheeseType()) in if loop, which will leads to compile time errors. change like this.

public int compareTo(Cheese anotherCheese)
   throws ClassCastException
   {
       if (!(anotherCheese instanceof Cheese))
            throw new ClassCastException("A Cheese object expected.");

       else return getCheeseType().compareTo(anotherCheese.getCheeseType()))

   }