How can Apache POI be used to deactivate a cell based on the selected value of another dropdown cell?

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Apache POI is a Java library that enables users to work with Microsoft Office documents, including Excel spreadsheets. To deactivate a cell based on the selected value of another dropdown cell using Apache POI, you can follow these steps:

1. Get the workbook object and the worksheet object where the dropdown cell and the cell to be deactivated are located.

Workbook workbook = WorkbookFactory.create(new File("sample.xlsx"));
Sheet worksheet = workbook.getSheetAt(0);

1. Get the dropdown cell and the cell to be deactivated using row and column indices.

Cell dropdownCell = worksheet.getRow(2).getCell(1);
Cell cellToDeactivate = worksheet.getRow(3).getCell(1);

1. Add a data validation rule for the dropdown cell to check for the allowed values.

DataValidationHelper dataValidationHelper = worksheet.getDataValidationHelper();
DataValidationConstraint constraint = dataValidationHelper.createExplicitListConstraint(
    new String[]{"OptionA", "OptionB", "OptionC"});
CellRangeAddressList addressList = new CellRangeAddressList(2, 2, 1, 1);
DataValidation validation = dataValidationHelper.createValidation(constraint, addressList);

worksheet.addValidationData(validation);

1. Add a conditional formatting rule for the cell to be deactivated based on the selected value of the dropdown cell.

ConditionalFormattingRule rule = sheet.getConditionalFormattingRules().createRule();
rule.createConditionalFormattingRule(ComparisonOperator.EQUAL, "OptionC");

CellRangeAddress[] cellRangeAddresses = { CellRangeAddress.valueOf("B4:B4") };
byte[] color = new byte[]{0, 0, 0};
PatternFormatting fill = rule.createPatternFormatting();
fill.setFillBackgroundColor(new XSSFColor(color));

sheet.getConditionalFormattingRules().addRule(rule);

In the example code above, the dropdown cell is located in cell B3 and the cell to be deactivated is located in cell B4. The dropdown cell allows values "OptionA", "OptionB", and "OptionC". If "OptionC" is selected, the cell B4 will be deactivated, which is achieved by adding a conditional formatting rule.

Note that this code is just an example and may need to be adjusted depending on your specific use case.