类的实例引起nullPointerException
我正在Eclipse中导入一个带poi的Excel 2007文件。 我的问题是一个NullPointerException ，但我不知道如何找出它来自哪里。 可能是类Data的实例有问题。 这是代码：
import java.io.*; import java.io.*; import java.util.ArrayList; import org.apache.poi.openxml4j.exceptions.InvalidFormatException; import org.apache.poi.ss.usermodel.Cell; import org.apache.poi.ss.usermodel.DateUtil; import org.apache.poi.ss.usermodel.Row; import org.apache.poi.ss.usermodel.Sheet; import org.apache.poi.ss.usermodel.WorkbookFactory; import org.apache.poi.ss.usermodel.Workbook; import org.apache.xmlbeans.XmlOptions; class Data{ public Data(){}; public Data(double[] codnt, int ctgr1, int ctgr2) { // super(); this.codnt = codnt; this.ctgr1 = ctgr1; this.ctgr2 = ctgr2; } double codnt[]; int ctgr1; int ctgr2; } class Center{ public Center(int cycle, Data[] c) { // super(); this.cycle = cycle; this.c = c; } int cycle; Data c[]; } public class KmeansCluster { @SuppressWarnings({ "static-access", "null" }) public static void main(String[] args)throws IOException,InvalidFormatException{ InputStream is = new FileInputStream(new File("src//artificial_exp1.xlsx")); Workbook wb = WorkbookFactory.create(is); Sheet sheet = wb.getSheetAt(0); ArrayList<Data> list = new ArrayList<Data>(); int i = 0; try { for (Row row : sheet) { Data dataTemp = new Data(); // int i = 0; int j = 0; for (Cell cell : row) { row.getCell(0).setCellType(cell.CELL_TYPE_NUMERIC); dataTemp.codnt[j] = cell.getNumericCellValue(); j++; System.out.println("cell.getnumericcellvalue() is " + cell.getNumericCellValue() + "datatemp.condt[j] is " + dataTemp.codnt[j]); System.out.println(" test passed !"); } dataTemp.ctgr1 = (int) dataTemp.codnt[j - 2]; dataTemp.ctgr2 = (int) dataTemp.codnt[j - 1]; list.add(dataTemp); i++; } Data data1 = (Data) list.get(0); System.out.println(data1.codnt[0] + " is the content of the first blank."); } catch (Exception e) { System.out.println(e.toString()); } } }
数据的无参数构造函数留下codnt未初始化。 您可以通过在通用exception块中打印堆栈跟踪来find它