--- title: How can you generate predictable Random numbers?... description: Explains that Java's Random class always produces a repeatable sequence of numbers determined by its seed, which is useful for writing deterministic tests.... canonical: https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How can you generate predictable Random numbers? #javalanguage #javacoding #javatips | daily.dev og:description: Explains that Java's Random class always produces a repeatable sequence of numbers determined by its seed, which is useful for writing deterministic tests.... og:url: https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey og:image: https://api.daily.dev/og/posts/xWfw0gGEY.png og:image:alt: How can you generate predictable Random numbers? #javalanguage #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 can you generate predictable Random numbers? #javalanguage #javacoding #javatips **[Java \(Official Oracle\)](https://daily.dev/sources/java-oracle)** · 1 min read · 0 upvotes · 0 comments ## Summary Explains that Java's Random class always produces a repeatable sequence of numbers determined by its seed, which is useful for writing deterministic tests. Without a supplied seed, the seed is derived from System.nanoTime. Notes that predictability differs from repeatability, and that SecureRandom should be used instead of Random for cryptographic or security-sensitive applications since it is harder to predict. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I generate the same sequence of random numbers every time in Java for testing? Create a Random instance with an explicit seed value; given the same seed, the Random class always produces the same sequence of numbers from methods like nextInt or nextDouble. Without a specified seed, Java derives one from System.nanoTime, making the sequence effectively unpredictable across runs. This repeatability is useful for writing deterministic unit tests. _Developers writing deterministic unit tests can find more Java API tips like this through daily.dev._ ### What's the difference between Random and SecureRandom in Java? Random produces a repeatable sequence based on a seed, which is predictable and unsuitable for security purposes even though it's fine for testing. SecureRandom is the preferred generator for cryptographic and security applications because, while its output still depends on a seed, that output is much harder to predict than standard Random. _Choosing between Random and SecureRandom comes up often when securing Java code, a topic daily.dev covers regularly._ ## Similar posts on daily.dev - [Ruby Random Numbers: How to Generate Them With Examples](https://daily.dev/posts/ruby-random-numbers-how-to-generate-them-with-examples-flyostzyh) · RUBYLAND · 0 upvotes · 0 comments - [Generate Valid and Unique Identifiers](https://daily.dev/posts/generate-valid-and-unique-identifiers-pebrzd1tw) · Baeldung · 3 upvotes · 0 comments - [The Random Numbers in Your Simulation Are Not Random. So Why Does Monte Carlo Work?](https://daily.dev/posts/the-random-numbers-in-your-simulation-are-not-random-so-why-does-monte-carlo-work--gd3fy0xyq) · Medium · 0 upvotes · 0 comments - [The little Random that could](https://daily.dev/posts/the-little-random-that-could-a4hxu0o5m) · RUBYLAND · 0 upvotes · 0 comments --- Tags: [#testing](https://daily.dev/tags/testing), [#java](https://daily.dev/tags/java) [View this post on daily.dev](https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"How can you generate predictable Random numbers? #javalanguage #javacoding #javatips","url":"https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey"},"datePublished":"2026-09-25T10:03:25.267Z","dateModified":"2026-09-25T10:03:40.767Z","description":"Explains that Java's Random class always produces a repeatable sequence of numbers determined by its seed, which is useful for writing deterministic tests....","image":"https://i.ytimg.com/vi/mhd_T3bQEeQ/sddefault.jpg","thumbnailUrl":"https://i.ytimg.com/vi/mhd_T3bQEeQ/sddefault.jpg","isAccessibleForFree":true,"articleSection":"Java (Official Oracle)","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Java (Official Oracle)","logo":"https://media.daily.dev/image/upload/s--SM9hIYUY--/f_auto,q_auto/v1773648791/logos/java-oracle?_a=BAMAMiiu0","url":"https://daily.dev/sources/java-oracle"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"testing,java","timeRequired":"PT1M","video":{"@type":"VideoObject","name":"How can you generate predictable Random numbers? #javalanguage #javacoding #javatips","description":"Explains that Java's Random class always produces a repeatable sequence of numbers determined by its seed, which is useful for writing deterministic tests....","thumbnailUrl":"https://i.ytimg.com/vi/mhd_T3bQEeQ/sddefault.jpg","uploadDate":"2026-09-25T10:03:25.267Z","duration":"PT1M","url":"https://api.daily.dev/r/xWfw0gGEY","embedUrl":"https://www.youtube.com/embed/mhd_T3bQEeQ"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Java (Official Oracle)","item":"https://daily.dev/sources/java-oracle"},{"@type":"ListItem","position":3,"name":"How can you generate predictable Random numbers? #javalanguage #javacoding #javatips"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/how-can-you-generate-predictable-random-numbers-javalanguage-javacoding-javatips-xwfw0ggey#faq","mainEntity":[{"@type":"Question","name":"How do I generate the same sequence of random numbers every time in Java for testing?","acceptedAnswer":{"@type":"Answer","text":"Create a Random instance with an explicit seed value; given the same seed, the Random class always produces the same sequence of numbers from methods like nextInt or nextDouble. 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