public class Semaphore {

  public Semaphore (int initialValue) { ; }

  // initialize a sempahore with value zero
  public Semaphore () { 
    this(0);
  }
    
  public void down () {
    // TODO: Implement this!
  }

  public void up () {
    // TODO: Implement this!
  }

  public static void main (String [] args) {
    // Semaphore test functionality

    final Semaphore semaphore = new Semaphore(1);

    for (int i=0;i < 4; i++) {
      final int threadID = i;

      Thread t = new Thread (new Runnable() {
	    public void run() {
	      System.out.println("[Thread " + threadID + 
		"] downing the semaphore");
	      semaphore.down();

	      System.out.println("[Thread " + threadID + 
		"] going to sleep");

	      try {
		Thread.sleep(1000);  // wait for 1 second
	      }
	      catch (InterruptedException iesx) {} // ignored
	      
	      System.out.println("[Thread " + threadID + 
		"] upping the semaphore");

	      semaphore.up();
	    }
	  });
      
      t.start();
    }
  }
}