simple about Semaphore usage

BoundedHashSet.java

public class BoundedHashSet<T> {
  private final Set<T> set;
  private final Semaphore sem;

  public BoundedHashSet(int bound) {
    set = Collections.synchronizedSet(new HashSet<T>());
    sem = new Semphore(bound);
  }

  public boolean add(T o) throw InterruptedException {
    sem.acauire();
    boolean wasAdded = false;
    try {
      wasAdded = set.add(o);
      return wasAdded;
    } finally {
      if(!wasAdded)
        sem.release();
    }
  }

  public boolean remove(Object o) {
    boolean wasRemoved = set.remove(o);
    if(wasRemoved)
      sem.release();
    return wasRemoved;
  }
}