// equalshashcode/SubtypeEquality.java

// (c)2017 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

import java.util.*;

enum Size { SMALL, MEDIUM, LARGE }

class Animal {

private static int counter = 0;

private final int id = counter++;

private final String name;

private final Size size;

Animal(String name, Size size) {

this.name = name;

this.size = size;

}

@Override

public boolean equals(Object rval) {

return rval instanceof Animal &&

// Objects.equals(id, ((Animal)rval).id) && // [1]

Objects.equals(name, ((Animal)rval).name) &&

Objects.equals(size, ((Animal)rval).size);

}

@Override

public int hashCode() {

return Objects.hash(name, size);

// return Objects.hash(name, size, id); // [2]

}

@Override

public String toString() {

return String.format("%s[%d]: %s %s %x",

getClass().getSimpleName(), id,

name, size, hashCode());

}

}

class Dog extends Animal {

Dog(String name, Size size) {

super(name, size);

}

}

class Pig extends Animal {

Pig(String name, Size size) {

super(name, size);

}

}

public class SubtypeEquality {

public static void main(String[] args) {

Set<Animal> pets = new HashSet<>();

pets.add(new Dog("Ralph", Size.MEDIUM));

pets.add(new Pig("Ralph", Size.MEDIUM));

pets.forEach(System.out::println);

}

}

/* Output:

Dog[0]: Ralph MEDIUM a752aeee

*/