compare objects doesnt work

Question

I'm trying to compare the names of objects of my own class Person so I can sort an ArrayList. I followed what my teacher did but can't seem to get why it doesn't work.

import java.util.*;

public class SortName implements Comparable<Person>{
    public int compare(Person p1, Person p2){
        return p1.getName().compareTo(p2.getName());
    }
}

what is the output? any error you got? – Dimuth Tharaka Menikgama Apr 18 '17 at 17:59 — Dimuth Tharaka Menikgama, Apr 18 '17 at 17:59

score 3 · Answer 1 · answered Apr 18 '17 at 18:02

3

It should be Comparator interface. Comparator interface has compare() method not Comparable.

public class SortName implements Comparator<Person>

answered Apr 18 '17 at 18:02

ProgrammerBoy

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score 2 · Accepted Answer · answered Apr 18 '17 at 17:59

The compare() method is correct, BUT you’re using the wrong interface. Implement Comparator, not Comparable. They’re easy to mix up.

import java.util.*;

public class SortName implements Comparator<Person>{
    public int compare(Person p1, Person p2){
        return p1.getName().compareTo(p2.getName());
    }
}

score 1 · Answer 3 · edited Mar 31 '18 at 17:59

1

You can try it with compareTo() method:

import java.util.*;

public class SortName implements Comparable<Person>{
    public int compareTo(Person p2){
        return this.getName().compareTo(p2.getName());
    }
}

edited Mar 31 '18 at 17:59

Karol Dowbecki

43,645
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answered Apr 18 '17 at 18:07

strash

1,291
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2

Its incorrect. compareTo() method of Comparable has does accept two arguments, Its compareTo(Object obj) – ProgrammerBoy Apr 18 '17 at 18:11

score 1 · Answer 4 · edited May 23 '17 at 12:32

Referring to What is the difference between compare() and compareTo()?

Comparator interface let you override its int compare(Object o1, Object o2) method.
Implementing this interface helps you to sort your inbuilt data structure or even a custom defined data data structure.

Comparable interface lets you override its int compareTo(Object o) method.
Example: (x.compareTo(y)==0) == (x.equals(y))

compare objects doesnt work

4 Answers4