How and Where to Use Iterators

How to use Iterators

Cells Iterator

There are various ways to access the cells' iterator, and one can use any of these methods based on the application requirements. Here are the methods that return the cells' iterator.

  1. Cells.iterator
  2. Row.iterator
  3. Range.iterator

All of the above mentioned methods return the iterator that allows to traverse the collection of cells which have been initialized.

The following code example demonstrates the implementation of the Iterator class for a cells collection.

// For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-Java
String dataDir = Utils.getDataDir(CellsIterator.class);
// Load a file in an instance of Workbook
Workbook book = new Workbook(dataDir + "sample.xlsx");
// Get the iterator from Cells collection
Iterator cellIterator = book.getWorksheets().get(0).getCells().iterator();
// Traverse cells in the collection
while (cellIterator.hasNext()) {
Cell cell = (Cell) cellIterator.next();
;
System.out.println(cell.getName() + " " + cell.getValue());
}
// Get iterator from an object of Row
Iterator rowIterator = book.getWorksheets().get(0).getCells().getRows().get(0).iterator();
// Traverse cells in the given row
while (rowIterator.hasNext()) {
Cell cell = (Cell) rowIterator.next();
System.out.println(cell.getName() + " " + cell.getValue());
}
// Get iterator from an object of Range
Iterator rangeIterator = book.getWorksheets().get(0).getCells().createRange("A1:B10").iterator();
// Traverse cells in the range
while (rangeIterator.hasNext()) {
Cell cell = (Cell) rangeIterator.next();
System.out.println(cell.getName() + " " + cell.getValue());
}
Rows Iterator

The Rows Iterator can be accessed while using the RowCollection.iterator method. The following code example demonstrates the implementation of the Iterator for RowCollection class.

// For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-Java
String dataDir = Utils.getDataDir(RowsIterator.class);
// Load a file in an instance of Workbook
Workbook book = new Workbook(dataDir + "sample.xlsx");
// Get the iterator for RowCollection
Iterator rowsIterator = book.getWorksheets().get(0).getCells().getRows().iterator();
// Traverse rows in the collection
while (rowsIterator.hasNext()) {
Row row = (Row) rowsIterator.next();
System.out.println(row.getIndex());
}
Columns Iterator

The Columns Iterator can be accessed while using the ColumnCollection.iterator method. The following code example demonstrates the implementation of the Iterator for ColumnCollection class.

// For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-Java
String dataDir = Utils.getDataDir(ColumnsIterator.class);
// Load a file in an instance of Workbook
Workbook book = new Workbook(dataDir + "sample.xlsx");
// Get the iterator for ColumnsCollection
Iterator colsIterator = book.getWorksheets().get(0).getCells().getColumns().iterator();
// Traverse columns in the collection
while (colsIterator.hasNext()) {
Column col = (Column) colsIterator.next();
System.out.println(col.getIndex());
}

Where to use Iterators

In order to discuss the advantages of using iterators, lets take a real time example.

Scenario

An application requirement is to traverse all cells in a given Worksheet to read their values. There could be several ways to implement this goal. A few are demonstrated below.

Using Display Range
// For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-Java
String dataDir = Utils.getDataDir(UsingDisplayRange.class);
// Load a file in an instance of Workbook
Workbook book = new Workbook(dataDir + "sample.xlsx");
// Get Cells collection of first worksheet
Cells cells = book.getWorksheets().get(0).getCells();
// Get the MaxDisplayRange
Range displayRange = cells.getMaxDisplayRange();
// Loop over all cells in the MaxDisplayRange
for (int row = displayRange.getFirstRow(); row < displayRange.getRowCount(); row++) {
for (int col = displayRange.getFirstColumn(); col < displayRange.getColumnCount(); col++) {
// Read the Cell value
System.out.println(displayRange.get(row, col).getStringValue());
}
}
Using MaxDataRow & MaxDataColumn
// For complete examples and data files, please go to https://github.com/aspose-cells/Aspose.Cells-for-Java
String dataDir = Utils.getDataDir(UsingMaxDataRowAndMaxDataColumn.class);
// Load a file in an instance of Workbook
Workbook book = new Workbook(dataDir + "sample.xlsx");
// Get Cells collection of first worksheet
Cells cells = book.getWorksheets().get(0).getCells();
// Loop over all cells
for (int row = 0; row < cells.getMaxDataRow(); row++) {
for (int col = 0; col < cells.getMaxDataColumn(); col++) {
// Read the Cell value
System.out.println(cells.get(row, col).getStringValue());
}
}

As you can observe that both of the above mentioned approaches use more or less similar logic, that is; loop over all cells in the collection to read the cell values. This could be problematic for a number of reasons as discussed below.

  1. The APIs such as MaxRow, MaxDataRow, MaxColumn, MaxDataColumn & MaxDisplayRange require extra time to gather the corresponding statistics. In case the data matrix (rows x columns) is large, using these APIs could impose performance penalty.
  2. In most of the cases, not all cells in a given range are instantiated. In such situations to check every cell in the matrix is not so efficient as compared to check only the initialized cells.
  3. Accessing a cell in a loop as Cells.get(rowIndex, columnIndex) will cause all cell objects in a range to be instantiated, which may eventually cause OutOfMemoryError.
Conclusion

Based on above mentioned facts, following are the possible scenarios where iterators should be used.

  1. Readonly access of the cell collection is required, that is; requirement is to only inspect the cells.
  2. Large number of cells are to be traversed.
  3. Only initialized cells/rows/columns are to be traversed.