--- title: How is String hash code calculated? - Cracking the Java... description: Java's String hashCode is computed as a polynomial hash of the string's characters using the prime number 31 as the base. The choice of 31 is intentional: it's... canonical: https://daily.dev/posts/how-is-string-hash-code-calculated---cracking-the-java-coding-interview-javacoding-javatips-ydobzmevm twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How is String hash code calculated? - Cracking the Java Coding Interview #javacoding #javatips | daily.dev og:description: Java's String hashCode is computed as a polynomial hash of the string's characters using the prime number 31 as the base. The choice of 31 is intentional: it's... og:url: https://daily.dev/posts/how-is-string-hash-code-calculated---cracking-the-java-coding-interview-javacoding-javatips-ydobzmevm og:image: https://api.daily.dev/og/posts/YdObZmEVm.png og:image:alt: How is String hash code calculated? - Cracking the Java Coding Interview #javacoding #javatips og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # How is String hash code calculated? - Cracking the Java Coding Interview #javacoding #javatips **[Java \(Official Oracle\)](https://daily.dev/sources/java-oracle)** · 1 min read · 0 upvotes · 0 comments ## Summary Java's String hashCode is computed as a polynomial hash of the string's characters using the prime number 31 as the base. The choice of 31 is intentional: it's prime, and 31-1=30... actually 31 is chosen because it and 29 (31-2) are both primes. For long strings, the JVM can leverage CPU SIMD instructions. Since String is immutable, the hash is computed lazily on first access and cached in a field. However, this caching technically makes String mutable (it modifies `hash` and `hashIsZero` fields), which prevents String from being a Java value class. ## Full article daily.dev links to this article rather than hosting it. 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