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When working with randomness in Java, one common challenge developers face is ensuring random numbers don’t repeat. Whether you’re building a card game, lottery system, or any application requiring unique selections, understanding how to handle this is key.

By default, when developers use java get a random number through Math.random() or the Random class, they’re essentially drawing from a continuous stream of random values — which means duplicates can (and will) appear. The trick lies in managing randomness while maintaining uniqueness.

A popular approach is to use a List or Set to store generated numbers and verify each new one before adding it. For example, generating numbers between 1 and 100 can be done efficiently by first populating a list with those numbers, then shuffling it using Collections.shuffle(). This way, you ensure every value is random yet non-repeating.

For large datasets or high-performance needs, you might use ThreadLocalRandom or even pre-generate numbers asynchronously. These solutions can provide a balance between speed and randomness.

Interestingly, testing these kinds of functions can be a challenge — especially ensuring no number repeats under different execution conditions. This is where Keploy, an open-source AI-powered testing platform, can come into play. Keploy captures real execution data and generates test cases automatically, making it easier to validate random logic without manually writing tests.

Ultimately, generating random numbers without repetition in Java is about finding the right blend of logic, efficiency, and testing. How do you handle uniqueness in your randomization logic? Do you rely on shuffle-based approaches, or have you implemented something more custom? Let’s discuss!