Can I use compareTo to sort integer and double values?

Question

Can I use compareTo to sort integer and double values? My system gives me an error that I Cannot invoke compareTo(int) on the primitive type int. any ideas?

Code:

public int compare(Object o1, Object o2) {  
Record o1C = (Record)o1;
Record o2C = (Record)o2;                
return o1C.getPrice().compareTo(o2C.getPrice());
}

class Record
    public class Record {
    String name;
    int price;    

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public int getPrice() {
        return price;
    }
    public void setPrice(int price) {
        this.price = price;
    }
}

As per the error message: `int` is a primitive, and therefore not an object. The `compareTo` method only works on objects. — , Jan 06 '13 at 02:03
Does this answer your question? [compareTo with primitives -> Integer / int](https://stackoverflow.com/questions/9150446/compareto-with-primitives-integer-int) — user202729, Feb 19 '22 at 13:19

score 25 · Answer 1 · answered Jan 06 '13 at 02:03

25

Well, the compiler's right :) You can't call compareTo directly. However, depending on the version of Java you're using, you can use Integer.compare (introduced in 1.7) and Double.compare (introduced in 1.4).

For example:

return Integer.compare(o1C.getPrice(), o2C.getPrice());

If you're not on 1.7 and still want to use built-in methods, you could use:

Integer price1 = o1C.getPrice();
Integer price2 = o2C.getPrice();
return price1.compareTo(price2);

... but this will use unnecessary boxing. Given that sorting a large collection can perform really quite a lot of comparisons, that's not ideal. It may be worth rewriting compare yourself, until you're ready to use 1.7. It's dead simple:

public static int compare(int x, int y) {
    return x < y ? -1
         : x > y ? 1
         : 0;
}

answered Jan 06 '13 at 02:03

Jon Skeet

1,421,763
867
9,128
9,194

public static int compare(int x, int y) { return x - y; } – Deepak Singhal Jan 06 '13 at 03:07
3

@Deepak: Absolutely not. That would be a broken implementation when `y` is a very large positive number and `x` is a very large negative number, due to overflow. – Jon Skeet Jan 06 '13 at 08:45
How do I use the static method? Can you add code to support that using price1 & price2? – Zen Apr 16 '16 at 09:31
@summers: You call the static method with the two prices, and the return value is the comparison... what problems have you had trying it? – Jon Skeet Apr 16 '16 at 10:04
Like; 'Integer price1 = o1C.getPrice(); Integer price2 = o2C.getPrice(); return compare(price1, price2);' – Zen Apr 16 '16 at 16:59
@summers: Right - so what went wrong when you tried that? – Jon Skeet Apr 16 '16 at 17:00
Works now. I'd made a typo back then. – Zen Apr 16 '16 at 17:05

score 14 · Answer 2 · edited Oct 22 '13 at 03:37

14

Change the code

int price;

to

Integer price;

because primitive types such as int will not support any methods, like compareTo().

edited Oct 22 '13 at 03:37

Michael Petrotta

59,888
27
145
179

answered Jan 06 '13 at 06:03

score 2 · Answer 3 · answered Jan 06 '13 at 03:06

In your current code; easier solution would be to just change this line and all will be good:

return o1C.getPrice() - o2C.getPrice() ;

This would work fine and good performance too because method compare() has only following requirement viz. return zero if both values are equal; else a positive/negative number.

Chiranjib Patra · Answer 4 · 2018-12-14T07:31:39.390

Step 1: Sort list by last name (for String values)

Collections.sort(peopleList, (p1, p2) -> 
                     p1.getLastName().compareTo(p2.getLastName()));

Step 2: Print all elements in the list

for (People ppl : peopleList) {
    System.out.print(ppl.getFirstName()+" - "+ppl.getLastName());
}

Step 1: Sort list by Age (for int values)

Collections.sort(peopleList, (p1, p2) -> p1.getAge() - (p2.getAge()));

Step 2: Print all elements in the list

for (People ppl : peopleList) {
    System.out.println(ppl.getAge());
}

Can I use compareTo to sort integer and double values?

4 Answers4

Linked

Related