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POJava: how to write proper equals method for classes that really do not have any state?
 

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    <p>Consider this interface:</p> <pre><code>public interface Listenable { void listen(); } </code></pre> <p>Consider this implementation:</p> <pre><code>public class Listener implements Listenable { public void listen() { System.out.println("I am listening"); } } </code></pre> <p>Now I am doing remoting via RMI and I am passing instances of such classes to server (maybe some black-magic proxies are spawn there, not sure).</p> <p>The only solution I was able to invent so far, <strong>and I have to say it's pretty idiotic</strong>, is to add this code to Listener class:</p> <pre><code>public class Listener implements Listenable { private double id; private Random rand = new Random(); public Listener() { this.id = rand.nextDouble(); } public void listen() { System.out.println("I am listening"); } public int hashCode() { ... } // calculate from id // same for equals - compare by id } </code></pre> <p>This <em>usually</em> works, but we all know how evil this is :/ How should one deal with such a situation?</p> <p><strong>UPDATE:</strong></p> <p>Stanard equals did not work for me, because instances are over different VMs (I mentioned remoting), so it couldn't work. I will need some state variable after all, or suggest something good for comparing such classes on remote VMs. I am very sorry for confusion. </p>
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    1. COWhy do you override `hashCode`?
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    2. COIf they don't have any meaningful state why are you trying to make an equals() method at all? This built-in can test for identity.
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    3. CO@Khackik if you override hashcode() you must override equals, thats part of the contract.
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