58 lines
1.5 KiB
Java
58 lines
1.5 KiB
Java
// equalshashcode/SubtypeEquality.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.*;
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enum Size { SMALL, MEDIUM, LARGE }
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class Animal {
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private static int counter = 0;
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private final int id = counter++;
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private final String name;
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private final Size size;
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Animal(String name, Size size) {
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this.name = name;
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this.size = size;
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}
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@Override public boolean equals(Object rval) {
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return rval instanceof Animal &&
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// Objects.equals(id, ((Animal)rval).id) && // [1]
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Objects.equals(name, ((Animal)rval).name) &&
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Objects.equals(size, ((Animal)rval).size);
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}
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@Override public int hashCode() {
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return Objects.hash(name, size);
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// return Objects.hash(name, size, id); // [2]
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}
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@Override public String toString() {
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return String.format("%s[%d]: %s %s %x",
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getClass().getSimpleName(), id,
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name, size, hashCode());
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}
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}
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class Dog extends Animal {
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Dog(String name, Size size) {
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super(name, size);
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}
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}
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class Pig extends Animal {
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Pig(String name, Size size) {
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super(name, size);
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}
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}
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public class SubtypeEquality {
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public static void main(String[] args) {
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Set<Animal> pets = new HashSet<>();
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pets.add(new Dog("Ralph", Size.MEDIUM));
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pets.add(new Pig("Ralph", Size.MEDIUM));
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pets.forEach(System.out::println);
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}
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}
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/* Output:
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Dog[0]: Ralph MEDIUM 931523a9
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*/
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