Randomizing File Lines With Java

  • 21/7/2014
  • One-minute read

When building trivia quizzes or smoke tests, you may need to shuffle text lines before processing them. The snippet below uses the NIO Files API and Collections.shuffle for clarity.

Sample Code

public static void main(String[] args) throws IOException {
    List<String> lines = Files.readAllLines(Paths.get("test.txt"));
    Collections.shuffle(lines);
    lines.forEach(System.out::println);
}

Notes

  • This approach loads the entire file into memory; for very large files, use a streaming algorithm with reservoir sampling.
  • Seed Collections.shuffle(lines, new Random(seed)) to reproduce the same order in tests.
  • Close resources or use try-with-resources when reading from channels or buffered readers directly.

References

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