@Override
   public boolean equals(Object obj) {
 	 if (this == obj) {
		return true;
 	 }
	 if (obj == null) {
		return false;
	 }
	 if (getClass() != obj.getClass()) {
		return false;
	 }
	 BigramModel<T,K> other = (BigramModel<T,K>) obj;
	 if (key == null) {
		if (other.key != null) {
			return false;
		}
	 } 
	 else if (!key.equals(other.key)) {
		return false;
	 }
	 if (value == null) {
		if (other.value != null) {
			return false;
		}
	 } 
	 else if (!value.equals(other.value)) {
		return false;
	 }
	 return true;
  }