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POJava: Get random line from a big file
 

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    <p>I've seen <a href="https://stackoverflow.com/questions/2218005/how-to-get-a-random-line-of-a-text-file-in-java">how to get a random line from a text file</a>, but the method stated there (the accepted answer) is running horrendously slow. It runs very slowly on my 598KB text file, and still slow on my a version of that text file which has only one out of every 20 lines, at 20KB. I never get past the "a" section (it's a wordlist).</p> <p>The original file has 64141 lines; the shortened one has 2138 lines. To generate these files, I took the Linux Mint 11 <code>/usr/share/dict/american-english</code> wordlist and used <code>grep</code> to remove anything with uppercase or an apostrophe (<code>grep -v [[:upper:]] | grep -v \'</code>). </p> <p>The code I'm using is</p> <pre><code>String result = null; final Random rand = new Random(); int n = 0; for (final Scanner sc = new Scanner(wordList); sc.hasNext();) { n++; if (rand.nextInt(n) == 0) { final String line = sc.nextLine(); boolean isOK = true; for (final char c : line.toCharArray()) { if (!(constraints.isAllowed(c))) { isOK = false; break; } } if (isOK) { result = line; } System.out.println(result); } } return result; </code></pre> <p>which is slightly adapted from <a href="https://stackoverflow.com/questions/2218005/how-to-get-a-random-line-of-a-text-file-in-java/2218067#2218067">Itay's answer</a>.</p> <p>The object <code>constraints</code> is a <code>KeyboardConstraints</code>, which basically has the one method <code>isAllowed(char)</code>:</p> <pre><code>public boolean isAllowed(final char key) { if (allAllowed) { return true; } else { return allowedKeys.contains(key); } } </code></pre> <p>where <code>allowedKeys</code> and <code>allAllowed</code> are provided in the constructor. The <code>constraints</code> variable used here has <code>"aeouhtns".toCharArray()</code> as its <code>allowedKeys</code> with <code>allAllowed</code> off.</p> <p>Essentially, what I want the method to do is to pick a random word <em>that satisfies the constraints</em> (e.g. for these constraints, "outvote" would work, but not "worker", because "w" is not in <code>"aeouhtns".toCharArray()</code>).</p> <p>How can I do this?</p>
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