The problem with compareTo method

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Hi! I have a problem with compareTo method. "Be sure that compareTo method returns different values for different objects". I've already checked in main method it - and I see that compareTo method returns different values for different objects. So what does codegym wants from me? Thanks in advance!

Implement the Comparable<Beach> interface in the Beach class. Beaches will be used by threads, so you need to ensure that all the methods are synchronized.
Implement the compareTo method so that when two beaches are compared the method returns a positive number if the first beach is better
or a negative number if the second beach is better. The magnitude of the number indicates how much better the beach is.

Requirements:

The Beach class must have three fields: String name, float distance, int quality.
The Beach class should implement the Comparable<Beach> interface.
The Beach class's compareTo method should at least account for beach quality and distance.
All of the Beach class's methods, except for the main method, must be synchronized.

package com.codegym.task.task17.task1714; /* Comparable */ import java.util.ArrayList; import java.util.Comparator; public class Beach implements Comparable<Beach> { private String name; private float distance; private int quality; public Beach(String name, float distance, int quality) { this.name = name; this.distance = distance; this.quality = quality; } public synchronized String getName() { return name; } public synchronized void setName(String name) { this.name = name; } public synchronized float getDistance() { return distance; } public synchronized void setDistance(float distance) { this.distance = distance; } public synchronized int getQuality() { return quality; } public synchronized void setQuality(int quality) { this.quality = quality; } public static void main(String[] args) { Beach beach1 = new Beach("Ocean", 2.5536f, 5); Beach beach2 = new Beach("Mary", 5.43f, 3); Beach beach3 = new Beach("Nice", 3.56f, 2); int who = beach1.compareTo(beach2); int who2 = beach2.compareTo(beach1); int who3 = beach1.compareTo(beach1); System.out.println(who); System.out.println(who2); System.out.println(who3); System.out.println(beach3.compareTo(beach1)); System.out.println(beach2.compareTo(beach3)); } @Override public synchronized int compareTo(Beach beach) { // if (this.quality == beach.quality) { // return 0; // } else if (this.quality > beach.quality) { // return 1; // } else { // return -1; // } return Comparator.comparing(Beach::getDistance) .thenComparing(Beach::getQuality) .compare(this, beach); } } //Implement the Comparable<Beach> interface in the Beach class. Beaches will be used by threads, so you need to ensure that all the methods are synchronized. //Implement the compareTo method so that when two beaches are compared the method returns a positive number if the first beach is better //or a negative number if the second beach is better. The magnitude of the number indicates how much better the beach is. // // //Requirements: //1. The Beach class must have three fields: String name, float distance, int quality. //2. The Beach class should implement the Comparable<Beach> interface. //3. The Beach class's compareTo method should at least account for beach quality and distance. //4. All of the Beach class's methods, except for the main method, must be synchronized.

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Lisa

Level 41

7 September 2021, 08:57

Hiho, I am not sure if my interpretation of the task is correct but at least it worked for me. The compareTo method must evaluate both, distance and quality. Your code evaluates quality only in one single case, when distance of the two objects is equal. But that is not a big problem, just don't use method references but a lambda and combine quality and distance using basic arithmetic (of course you won't need thenComparing anymore). Or just use Float.compare... then you save same typing. Yeah, yeah... that's a good attempt and you can use that knowledge later for sure 🤪😜

Vitalina

Level 20 , Poland

7 September 2021, 14:52

Hi! Thank you very much for helop. i understood what you meant. but I don't know how to write it in code. I'v tried the code below. But it didn't accept it. float f1 = this.quality; float f2 = this.distance; int f3 = Float.compare(f1, f2); float s1 = beach.quality; float s2 = beach.distance; int s3 = Float.compare(s1, s2); if (f3 == s3) { return 0; } else if (f3 > s3){ return 1; } else { return -1; }

Lisa

Level 41

7 September 2021, 15:49

solution

That's to fix your first attempt. Is that some copy/ paste solution you tried? Then you should follow your second attempt

// I've split it into Comparator declaration and the final comparing, that's necessary to be able to define the type (as there is no more method that specifies it - you of course could write one instead)
// I think you can use any basic arithmetic you want but + or - should be best suited as there's no rounding involved
Comparator<Beach> byDistAndQuality = Comparator.comparing(o -> o.getDistance() + o.getQuality());
return byDistAndQuality.compare(this, beach);

compareTo returns an int that reflects if this is bigger or smaller (better or worse) than the passed beach variable. So it is helpful to declare a int rating = 0; variable to hold intermediate results. First you check if this.quality is > beach.quality and add or subtract 1 from rating. Then you do the same for distance and return rating. That's all... I'd go with that way to get used to the compareTo method You also could use Float.compare(o1, o2). That compares two floats. Just use this.distance + (or) - this.quality as the first float and beach.distance +- beach.quality as the other. But as said... try the middle approach first. With using either + or - you can weight distance and quality. Yeah, yeah... good luck 😜🤪

Vitalina

Level 20 , Poland

7 September 2021, 16:42

This code below codegym didn't accept. Comparator<Beach> byDistAndQuality = Comparator.comparing(o -> o.getDistance() + o.getQuality()); return byDistAndQuality.compare(this, beach); I wrote the new code according to your instructions but I think it doesn't work well. int rating = 0; if (this.quality == beach.quality) { rating = rating + 0; } else if (this.quality > beach.quality) { rating = rating + 1; } else { rating = rating - 1; } if (this.distance == beach.distance) { rating = rating + 0; } else if (this.distance > beach.distance) { rating = rating + 1; } else { rating = rating - 1; } return rating;

Lisa

Level 41

7 September 2021, 17:19

It didn't validate or you just don't like it cause it looks a bit messy? If it's the latter you could beautify it (but that's just a matter of taste).

int rating = 0;
if ( this.distance > beach.distance ) rating++;
else if ( this.distance < beach.distance ) rating--;

And I don't know why the comparing approach won't validate and unfortunately I can not test it anymore.

Vitalina

Level 20 , Poland

7 September 2021, 17:53

Yes, your code is more beautiful. I'v tried it but it still won't validate the 3rd requirement. Thank you very much for help and for your time!

Lisa

Level 41

7 September 2021, 18:00

crazy, crazy... I'm sure this has to work... maybe try to reset the task and retry. And if that does not help you could try to flip > < in if and else if (but I doubt that is the problem). Unfortunately I validated using Float.compare so I'm not 100% sure about that solution (but at least to 99.99% 🤪😜)

Vitalina

Level 20 , Poland

7 September 2021, 18:25

I've finally passed this task!!!!🙌 I've tried Float.compare.. float f1 = Float.compare(this.distance, beach.distance); float f2 = Float.compare(this.quality, beach.quality); return Float.compare(f1, f2); Thank you very much! I really don't know why it was so difficult. But I know a lot about compareTo() method and Float.compare(p1, p2) method now.😏😁

Angel Stefan

Level 23 , Sibiu, Romania

30 January 2022, 15:00

Nice solution! So, when we need to compare two primitive var. we can use the wrapper Class.compareTo();