Exception in thread main javalangIllegalStateException Cannot get a NUMERIC value from a STRING cell at orgapachepoixssfusermodelXSSFCelltypeMismatchXSSFCelljava987 at orgapachepoixssfusermodelXSSFCel

This exception is thrown when you are trying to retrieve a numeric value from a cell that contains a string value.

In your specific case, the exception is thrown at line 30 of the "ExcelToLineChart.java" file, where you are trying to call the getNumericCellValue() method on a cell that contains a string value.

To fix this issue, you need to make sure that you are retrieving the correct type of value from the cell. If the cell contains a string value, you should use the getStringCellValue() method instead of getNumericCellValue().

Here is an example of how to handle this situation:

Cell cell = row.getCell(columnIndex);
if (cell.getCellType() == CellType.STRING) {
    String cellValue = cell.getStringCellValue();
    // handle the string value
} else if (cell.getCellType() == CellType.NUMERIC) {
    double cellValue = cell.getNumericCellValue();
    // handle the numeric value
} else {
    // handle other cell types if necessary
}

By checking the cell type before retrieving the value, you can avoid the IllegalStateException and handle different types of cell values appropriately