Understanding object references and method call in Java

import java.util.Scanner;
 
public class Characteristic {
 
private String description;
private int rating;
 
public Characteristic(String desc) {
 description = desc;
 rating = 0;
}
 
public static void main(String[] args) {
 
 
 Characteristic likesSports = new Characteristic("likes sports");
 Characteristic likesBeaches = new Characteristic("likes beaches");
 
 likesSports.setRating();
 
 System.out.println("Displaying the rating we got: " +  likesSports );
System.out.println();
 
  likesBeaches.setRating();
System.out.println("Displaying the rating we got: " + likesBeaches );
 System.out.println();
 
 
 Characteristic sueLikesFishing = new Characteristic("likes fishing");
 sueLikesFishing.setRating(6);
 
 Characteristic bobLikesFishing = new Characteristic("likes fishing");
 bobLikesFishing.setRating(6);
 
 System.out.println("Compatibility measure should be 1");
 System.out.println("\t" + sueLikesFishing.getCompatibility(bobLikesFishing));
 
 System.out.println("Compatibility measure should be 0");
 System.out.println("\t" + sueLikesFishing.getCompatibility(likesSports));
 
 sueLikesFishing.setRating(1);
 bobLikesFishing.setRating(9);
 
 System.out.println("Compatibility measure should be 0.209");
 System.out.println("\t" +
sueLikesFishing.getCompatibility(bobLikesFishing));
 
 sueLikesFishing.setRating(2);
 bobLikesFishing.setRating(9);
 System.out.println("Compatibility measure should b e about 0.395");
System.out.println("\t" +
sueLikesFishing.getCompatibility(bobLikesFishing));
 
}
 
private boolean isValid(int aRating){
 return(aRating>=1 && aRating<=10);
}
 
/*(5) Enter comments here */
public void setRating(int aRating){
  if(isValid(aRating))
   rating = aRating;
}
 
public void setRating(){
 System.out.println("What is your rating for " + description + "?");
System.out.println("Please enter an integer from 1 to 10");
 
 Scanner reader = new Scanner(System.in);
 int data = -1;
 boolean needTheRating = true;
 
 while(needTheRating){
   data = reader.nextInt();
   if(isValid(data)){
   needTheRating = false;
  } else {
  System.out.println("Sorry, that rating is out of range.");
  System.out.println("Please enter an integer from 1 to 10");
 }
}
 
setRating(data);
}
 
public String toString(){
 return description + " is rated as " + rating;
}
 
public String getDescription() {
 return description;
}
 
public int getRating(){
 return rating;
}
 
public double getCompatibility(Characteristic otherRating){
 if(!isMatch(otherRating))
   return 0.0;
 else
   return getCompatibilityMeasure(otherRating);
}
 
private boolean isMatch(Characteristic otherRating){
 return
description.equals(otherRating.getDescription());
}
 
private double getCompatibilityMeasure(Characteristic otherRating){
 int r1 = rating;
 int r2 = otherRating.getRating();
 
 if(r1==0 || r2==0){
   return 0.0;
 } else {
   return (1.0 - (r1 - r2)*(r1 - r2)/81.0);
}
}
 
}

                                  

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