https://aamernabi.github.io/tags/collections/ Recent content in Collections on Aamer Paul Hugo en-us Sun, 26 Jul 2020 23:03:02 +0530 https://aamernabi.github.io/posts/java-hashcode/ Sun, 26 Jul 2020 23:03:02 +0530 https://aamernabi.github.io/posts/java-hashcode/ <p>In Java, the <code>hashCode()</code> method, inherited from the <code>Object</code> class, plays a crucial role in the efficient functioning of hash-based collections like <code>HashMap</code>, <code>HashSet</code>, and <code>Hashtable</code>. It generates an integer hash code value for an object, which is used to determine the &ldquo;bucket&rdquo; where the object should be stored.</p> <h2 id="the-hashcode-and-equals-contract">The <code>hashCode()</code> and <code>equals()</code> Contract</h2> <p>The most important concept to understand is the contract between <code>hashCode()</code> and <code>equals()</code>:</p> <blockquote> <ol> <li>If two objects are equal according to the <code>equals(Object)</code> method, then calling the <code>hashCode()</code> method on each of the two objects must produce the same integer result.</li> <li>It is <em>not</em> required that if two objects are unequal according to the <code>equals(Object)</code> method, then calling the <code>hashCode()</code> method on each of the two objects must produce distinct integer results. However, producing distinct hash codes for unequal objects may improve the performance of hash tables.</li> </ol></blockquote> <p>In simple terms: <strong>equal objects must have equal hash codes.</strong></p>