TableSlice extends Relation { @Override public List<Column<?>> columns() { List<Column<?>> columns = new ArrayList<>(); for (int i = 0; i < columnCount(); i++) { columns.add(column(i)); } return columns; } TableSlice(Table table, Selection rowSelection);  TableSlice(Table table); @Override Column<?> column(int columnIndex); @Override Column<?> column(String columnName); @Override int columnCount(); @Override int rowCount(); @Override List<Column<?>> columns(); @Override int columnIndex(Column<?> column); @Override Object get(int r, int c); @Override String name(); Table getTable(); @Override void clear(); void removeSort(); void removeSelection(); @Override List<String> columnNames(); @Override TableSlice addColumns(Column<?>... column); @Override TableSlice removeColumns(Column<?>... columns); @Override Table first(int nRows); @Override TableSlice setName(String name); Table asTable(); double reduce(String numberColumnName, NumericAggregateFunction function); @Override Iterator<Row> iterator(); int mappedRowNumber(int rowNumber); void sortOn(Sort key);  }
@Test public void columns() { TableSlice slice = new TableSlice(source, Selection.withRange(0, source.rowCount())); assertEquals(source.columns().get(0).size(), slice.columns().get(0).size()); }