Compare objects of other class

Question

I'm having trouble comparing objects of another class, how should I proceed?
I made a tasty example, hopefully the code should be self-explanatory.

cake.java:

public class Cake implements Comparable<Cake> {

  private final int tastyness;

  public Cake(tastyness) {
    this.tastyness = tastyness;
  }

  public int compareTo(Cake other) {
    return this.tastyness - other.tastyness;
  }
}

makeBestDinner.java:

public class makeBestDinner {

  List<Cake> cakes = new ArrayList<cake>();
  // Make a whole lot of cakes here
  if (cakes[0] > cakes[1]) {
    System.out.println("The first cake tastes better than the second");
  }

  // Do the same for beverages
}

Why didn't you use `compareTo` method when you have already overridden it? — Rohit Jain, Apr 10 '13 at 09:42
Duplicate: http://stackoverflow.com/questions/8946071/java-compareto-and-operators — halex, Apr 10 '13 at 09:42

score 2 · Accepted Answer · answered Apr 10 '13 at 09:43

Java does not support operator overloading hence following will not work.

  if (cakes[0] > cakes[1]) {

instead, you should

if (cakes.get(0).compareTo(cakes.get(1)) > 0) {

Also to get elements from list we need to call list.get(index) not

list[index]

So following code will not work.

List<Cake> cakes = new ArrayList<cake>();
// Make a whole lot of cakes here
if (cakes[0] > cakes[1]) {

freddy.smith · Answer 2 · 2013-04-10T10:06:58.960

1

if(cakes.get(0).compareTo(cakes.get(1)) > 0) {
    System.out.println("The first cake tastes better than the second");
}

edited Apr 10 '13 at 10:06

answered Apr 10 '13 at 09:42

freddy.smith

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score 0 · Answer 3 · answered Apr 10 '13 at 09:41

0

You shoud use if (cakes[0].compareTo( cakes[1]))>0) instead

answered Apr 10 '13 at 09:41

BlackJoker

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Thank you, this solution worked! However, I was under the impression that the '<' operator should work when a compareTo method is defined? When trying to use '<', I get: **The operator < is undefined for the argument type(s) oving9.SokobanResult, oving9.SokobanResult** even though Comparable is implemented in oving9.SokobanResult. – user1803704 Apr 10 '13 at 09:45

Simulant · Answer 4 · 2013-04-10T10:20:35.130

0

use the following:

if (cakes.get(0).compareTo(cakes.get(1)) > 0) {
    System.out.println("The first cake tastes better than the second");
}

and read the Comparable documentation

edited Apr 10 '13 at 10:20

answered Apr 10 '13 at 09:42

Simulant

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The Ice Mage · Answer 5 · 2013-04-10T10:46:52.830

0

if (cakes[0] > cakes[1])...

Is there not a problem here? As people have said, you should use if(cakes[0].compareTo(cakes[1]) > 0) Well I would say that BUT you're using an ArrayList. Can you really get elements by typing listname[elementnumber]? I thought you have to use listname.get(elementnumber).

edited Apr 10 '13 at 10:46

answered Apr 10 '13 at 09:47

The Ice Mage

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Compare objects of other class

5 Answers5