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POChecking for and Removing elements in Java HashMap
 

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  1. POChecking for and Removing elements in Java HashMap
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    <p>I am trying to check for and remove elements, using a HashMap in Java. Its keys are a type I created called ClusterKey, and its values are a type I created called ClusterValue.</p> <p>Here is the code that is causing issues:</p> <pre><code>ClusterKey ck = new ClusterKey(Long.parseLong(split[0].split("=")[1]), Integer.parseInt(split[1].split("ey")[1])); if (arg == 0) keys.put(ck, new ClusterValue(index, false)); if (arg == 1) { if (keys.containsKey(ck)) { index = keys.get(ck).messageNo; keys.remove(ck); } keys.put(ck, new ClusterValue(index, true)); } </code></pre> <p>The problem is that even when the ClusterKey is the same as an existing ClusterKey, containsKey() and remove() do not seem to recognize it as equal. I have implemented equals() in class ClusterKey to override Java's equals() method, as follows:</p> <pre><code>class ClusterKey { long firstKey; int secondKey; public ClusterKey(long firstKey, int secondKey) { this.firstKey = firstKey; this.secondKey = secondKey; } public boolean equals(Object otherKey) { return this.firstKey == ((ClusterKey) otherKey).firstKey &amp;&amp; this.secondKey == ((ClusterKey) otherKey).secondKey; } } </code></pre> <p>So, I'm quite confused. Thanks so much for your help.</p> <p>Regards, Rebecca</p> <p>UPDATE: Thank you for your advice and feedback on my code. I was able to solve the problem by adding hashCode() to ClusterKey, as follows:</p> <pre><code> } public boolean equals(Object otherKey) { return this.firstKey == ((ClusterKey) otherKey).firstKey &amp;&amp; this.secondKey == ((ClusterKey) otherKey).secondKey; } public int hashCode() { return (int) firstKey + secondKey; } </code></pre>
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    1. USLa-comadreja
    1. USLa-comadreja
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    1. CODid you implement `hashCode`? That `hash` part is important.
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      1. USDave Newton
    2. CORight, _always_ implement `equals()` and `hashCode()` together.
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      1. USGriffeyDog
    3. COYou should be able to just call `put()`, without removing the key first (it'll overwrite, once you deal with `hashCode()`). Beyond that, I'm a little suspicious about the use of `arg`, as it looks like you're using it as a boolean argument, which isn't good practice.
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      1. USClockwork-Muse
 

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