magicalland.java

import java.util.HashSet;
import java.util.Set;

public class MagicalLand {
  public static void main(String[] args) {
    for (int i = 0; i < (Math.random() * 500) + 2; i++) {
      if (Unicorn.pat()) {
        System.out.println("UNICORN #1: PAT THIS UNICORN ONCE");
      }
    }

    for (int i = 0; i < (Math.random() * 500) + 2; i++) {
      if (Unicorn.pat()) {
        System.out.println("UNICORN #2: PAT THIS UNICORN ONCE");
      }
    }
    System.out.println("END OF PROGRAM");
  }
}

class Unicorn {
  private static final Set<StackTraceElement> set = new HashSet<StackTraceElement>();

  public static boolean pat() {
    return set.add(Thread.currentThread().getStackTrace()[2]);
  }
}