private void beInitialized(DataContainer<E[]> container) {
if (rows == null) { // initialize on the first invocation
rows = new ArrayList<E[]>();
while (source.next(container) != null) rows.add(container.getData());
columnIndex = 0;
}
}
@Override
public DataContainer<E[]> next(DataContainer<E[]> container) {
beInitialized(container);
if (rows.size() == 0 || columnIndex >= rows.get(0).length) return null;
@SuppressWarnings("unchecked")
E[] column = ArrayUtil.newInstance((Class<E>) source.getType().getComponentType(), rows.size());
for (int rowIndex = 0; rowIndex < rows.size(); rowIndex++) {
E[] row = rows.get(rowIndex);
column[rowIndex] = (columnIndex < row.length ? row[columnIndex] : null);
}
columnIndex++;
return container.setData(column);
}