Exception in thread "main" java.lang.NullPointerException 5

Question

        java.io.FileNotFoundException: votes.txt (The system cannot find the file specified)

        Exception in thread "main" java.lang.NullPointerException



    I was unable to fix this , please help me

       Exception in thread


    package MayorRace;




                public class MayorRace {

                   public static void main(String[] args)
                   {
                       int[][] Matrix1 = load("votes.txt");
                       int[][] Matrix2 = load("votes1.txt");
                    AT THIS LINE
                       printAll(Matrix1);
                       printAll(Matrix2);
                   }

                   @SuppressWarnings("resource")
                private static int[][] load(String filename)
                   {
                       ArrayList<ArrayList<Integer>> data = new ArrayList<ArrayList<Integer>>();
                       BufferedReader in = null;
                       // For now, we are assuming the text file is in the correct format
                       try
                       {
                           in = new BufferedReader(new FileReader(new File(filename)));
                           String dataLine;

                           while ((dataLine = in.readLine()) != null)
                           {
                               StringTokenizer tokenizer = new StringTokenizer(dataLine);
                               ArrayList<Integer> temp = new ArrayList<Integer>();
                               while (tokenizer.hasMoreTokens())
                               {
                                   temp.add(Integer.parseInt(tokenizer.nextToken()));
                               }
                               data.add(temp);
                           }
                       }  catch (FileNotFoundException ex )
                       {
                           System.out.println(ex);
                           return null;
                       } catch (IOException ex)
                       {
                           return null;
                       }
                       return convertmatrix(data);

                   }

// TODO Auto-generated method stub

                   private static int[][] convertmatrix(ArrayList<ArrayList<Integer>> integers)
                   {
                       int coloumns = integers.size();
                       if (coloumns == 0)
                       {
                           return null;
                       }
                       int rows = integers.get(0).size();
                       if (rows== 0)
                       {
                           return null;
                       }
                       int[][] output = new int[coloumns][rows];
                       for (int i = 0; i < coloumns; i++)
                       {
                           for (int j = 0; j < rows; j++)
                           {
                               output[i][j] = integers.get(i).get(j);
                           }
                       }
                       return output;
                   }

// TODO Auto-generated method stub GETSUM METHOD private static int[] getsum(int[][] matrix) { AT THIS LINE int[] sum = new int[matrix[0].length];

                       for (int i = 0; i < matrix[0].length; i++)
                       {
                           for (int[] matrixColumn : matrix)
                           {
                               sum[i] += matrixColumn[i];
                           }
                       }
                            return sum;
                   }



                   private static float[] getPer(int[] sum)
                   {
                       float total = 0;
                       for (int i = 0; i < sum.length; i++)
                       {
                           total += sum[i];
                       }
                       float[] per = new float[sum.length];
                       for (int i = 0; i < sum.length; i++)
                       {
                           per[i] = (sum[i] / total) * 100.0f;
                       }
                       return per;
                   }


     GETTOPTWO METHOD
                   private static int[] getTopTwo(float[] totals)
                   {
                       float max = 0.0f;
                       int value1 = 0;
                       int value2 = 0;
                       for (int i = 0; i < totals.length; i++)
                       {
                           if (max < totals[i])
                           {
                               max = totals[i];
                               value2 = value1;
                               value1 = i;
                           }
                       }
                       int[] output =
                       {
                           value1, value2
                       };
                       return output;
                   }
     PRINTMATRIX METHOD
                   private static void printMatrix(int[][] matrix)
                   {
                       if (matrix != null)
                       {
                           System.out.print("\t");
                           for (int i = -2; i < matrix.length; i++)
                           {
                               if (i == -1)
                               {
                                   System.out.print("Precinct");
                               }
                               else if (i >= 0)
                               {
                                   System.out.print(i + 1);
                               }
                               for (int j = 0; j < matrix[0].length; j++)
                               {
                                   if (i == -2)
                                   {
                                       System.out.print("Candidate\t");
                                   }
                                   else if (i == -1)
                                   {
                                       System.out.print("    " + (char) (65 + j) + "\t\t");
                                   }
                                   else
                                   {
                                       System.out.print("\t   " + matrix[i][j] + "\t");
                                   }
                               }
                               System.out.println();
                           }
                       }
                   }
     //METHOD 
                   private static void printTotal(int[] totals)
                                TODO Auto-generated method stub
                   {
                       System.out.print("sum ");
                       for (int i = 0; i < totals.length; i++)
                       {
                           System.out.print("\t   " + totals[i] + "\t");
                       }
                       System.out.println();
                   }

                   private static void printPercentages(float[] per)
                   {
                       System.out.print("\nPercentage");
                       for (int i = 0; i < per.length; i++)
                       {
                           System.out.print(String.format(" %.1f           ", per[i]));
                       }
                       System.out.println();
                   }

                   private static void printWinner(float[] per)
                   {
                       int champ = -1;
                       for (int i = 0; i < per.length; i++)
                       {
                           if (per[i] > 50)
                           {
                               champ = i;
                           }
                       }
                       if (champ != -1)
                       {
                           System.out.println("Candidate "+(char)(65+champ)+ " is the winner");
                       }
                       else
                       {
                           int[] topTwo = getTopTwo(per);
                           System.out.println("\nThere is a run-off between candidate "
                                   + (char) (65 + topTwo[0]) + " and " + (char) (65 + topTwo[1]));
                       }
                   }

                   private static void printAll(int[][] matrix)
                   {
//EXCEPTION // TODO Auto-generated method stub
                     AT THIS LINE
                       int[] sum = getsum(matrix);
                       float[] per = getPer(sum);
                       printMatrix(matrix);
                       printTotal(sum);
                       printPercentages(per);
                       printWinner(per);
                       System.out.println();
                   }

                            private static void printTable(int[][] matrix) {

                                      // TODO Auto-generated method stub
                                      // TODO Auto-generated method stub

                            }
                }

PLEASE HELP ME TO FIX THIS

Answer 1

"java.io.FileNotFoundException: votes.txt (The system cannot find the file specified)

You catch this error and set the matrix to null

  catch (FileNotFoundException ex )
  {
     System.out.println(ex);
     return null;
  }

And then when you want to use your matrix in the printAll method you get the NPE on

matrix[0].length

Answer 2

Your program load method has FileNotFoundException, and because of it, method load returns null . You need to check if load method has passed successfully, before printing matrix:

               int[][] matrix1= load("votes.txt");
               if(matrix1 != null){ // in this case an exception has occured during read
                  printAll(matrix1);
               }else{
                 System.out.println("Could not load file into matrix");
               }

Without it, you will got an NPE during

int[] sum = new int[matrix[0].length];

because matrix is null

UPDATE :

For me it is working fine, if I replace main body with:

public static void main(String[] args) {
    int[][] matrix1 = load("c://Downloads//votes.txt");
    if (matrix1 != null) {
        printAll(matrix1);
    }
}

votes.txt content:

1 1 1 1 1 1

Tips: Lists of lists is created by:

List<List<Integer>> data = new ArrayList<List<Integer>>();

or in jdk7++

List<List<Integer>> data = new ArrayList<>();

Name you variables, starting by lowerCase, so matrix1 , matrix2 , NOT: Matrix1,Matrix2.