public Class<?> getColumnClass(int n) {
		if (columnClasses == null)
			throw new IllegalStateException("columnClasses not set");
		int max = columnClasses.length;
		if (n>=max)
			throw new ArrayIndexOutOfBoundsException(
			"columnClasses has " + max + " elements; you asked for " + max);
		return columnClasses[n];
	}