@Override
    public boolean equals(Object obj) {
    	if (this == obj)
    		return true;
    	if (obj == null)
    		return false;
    	if (getClass() != obj.getClass())
    		return false;
    	Occurrence other = (Occurrence) obj;
    	if (word == null) {
    		if (other.word != null)
    			return false;
    	} else if (!word.equals(other.word))
    		return false;
    	return true;
    }