code: public E get(int x, int y) {
  		if (columns.size() < x) {
  			columns.set(x, new ArrayList<>());
  		}
  		ArrayList<E> columnList = columns.get(x);
  		if (columnList.size() < y) {
  			columnList.set(y, this.defaultElement);
  		}
  		return columnList.get(y);
  	}
docs: Returns the element in column {@code x} and y {@code y}
  
  @param x The column of the element
  @param y The row of the element
  @return the element at (x, y)