fisher-yates-knuth-shuffle.java

public class Main {
  public static void main ( String args [] ) {
    int size = 392000000;
    int sampleSize = 20000;
    System.err.println("Start: allocation");
    int [] array = new int[size];
    System.err.println("Done: allocation");
    java.util.Random rnd = new java.util.Random();

    System.err.println("Start: population w/line numbers");
    for ( int ii = 0; ii < size; ++ii ) {
      array[ii] = ii+1;
    }
    System.err.println("Done: population w/line numbers");
    
    System.err.println("Start: shuffle");
    for ( int ii = 0; ii < size; ++ii ) {
      int newPos = rnd.nextInt(size);
      int tmp = array[ii];
      array[ii] = array[newPos];
      array[newPos] = tmp;
    }
    System.err.println("Done: shuffle");

    for ( int ii = 0; ii < sampleSize; ++ii ){
      System.out.println("" + array[ii]);
    }
  }
}

// javac Main.java
// time java -Xmx4096M Main > results.txt