java - Extracting Excell cell value in a array -

i using apache poi extract data excel sheet , trying save extracted values in array.

i getting java.lang.nullpointerexception error.

i searched it, , apparently exception triggered when try assign value object value null.

i tried many example, example codes print out cell value. want save them in array perform calculation.

package excelltotext; import java.io.*; import java.lang.*; import java.util.*;  import org.apache.poi.hssf.usermodel.hssfcell; import org.apache.poi.hssf.usermodel.hssfsheet; import org.apache.poi.hssf.usermodel.hssfworkbook; import org.apache.poi.ss.usermodel.cell; import org.apache.poi.ss.usermodel.formulaevaluator; import org.apache.poi.ss.usermodel.row; import org.apache.poi.xssf.usermodel.xssfsheet; import org.apache.poi.xssf.usermodel.xssfworkbook; public class convert {      @suppresswarnings("null")     public static void main(string[] args) throws ioexception {         double []  modify = null ;         fileinputstream fs = new fileinputstream(new file ("book1.xlsx"));         xssfworkbook wb = new xssfworkbook(fs);         xssfsheet sheet = wb.getsheetat(0);         formulaevaluator formulaevaluater = wb.getcreationhelper().createformulaevaluator();         (row row:sheet)         {             int  num = 0;             for(cell  cell : row){                  switch (formulaevaluater.evaluate(cell).getcelltype())                 {                 case cell.cell_type_numeric:                  modify [num] = ( cell.getnumericcellvalue());                 num += num;                 }                 system.out.println(modify[num]);            }         }      }   } 

any suggestions appreciated.

your modify array null num += num; give npe. need create array egzample double [] modify = new double[1000]; instead of double [] modify = null ;