private void checkIndex(int idx) throws SQLException {
        if (idx < 1 || idx > RowSetMD.getColumnCount()) {
            throw new SQLException(resBundle.handleGetObject("cachedrowsetimpl.invalidcol").toString());
        }
    }
Checks to see whether the given index is a valid column number
in this <code>CachedRowSetImpl</code> object and throws
an <code>SQLException</code> if it is not. The index is out of bounds
if it is less than <code>1</code> or greater than the number of
columns in this rowset.
<P>
This method is called internally by the <code>getXXX</code> and
<code>updateXXX</code> methods.

@param idx the number of a column in this <code>CachedRowSetImpl</code>
           object; must be between <code>1</code> and the number of
           rows in this rowset
@throws SQLException if the given index is out of bounds
src/main/java/org/replicadb/rowset/sun/rowset/CachedRowSetImpl.java