Matrix:
[ 9 27 38  ]
  23 9 30  ]
  35 12 15  ]
Enter the file name with extension : file.txt
3
3
9 27 38 
23 9 30 
35 12 15 
Exception in thread "main" java.lang.NullPointerException
	at matrix.Main.main(Main.java:27)
C:\Users\nastya\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1
СБОРКА ЗАВЕРШЕНА СО СБОЕМ (общее время: 16 секунды)

package matrix;

import java.io.IOException;
import java.util.LinkedList;
import java.util.List;

public class Main {

    public static void main(String[] args) throws MatrixIndexException, IOException {
        Matrix m1 = new Matrix1D(3, 3);
        //Matrix m2 = new Matrix1D(100, 100);
        
        MatrixUtils.fillByRandom(m1);
        //MatrixUtils.fillByRandom(m2);
        
        //Matrix m = MatrixUtils.matrixMultiple(m1, m2);
        
        System.out.println(m1.toString());
        MatrixUtils.writeMatrixToFile(m1, "file.txt");
        
        Matrix m3 = MatrixUtils.loadMatrixFromFile("file.txt");
        System.out.println(m3.toString()); ---------------------------вот здесь говорят ошибка
    }

 public static void writeMatrixToFile(Matrix m, String filename) {

        try (FileWriter writer = new FileWriter(filename, false)) {
            String strForWrite = "";

            writer.write(String.valueOf(m.getRowCount()));
            writer.write("\n");
            writer.write(String.valueOf(m.getColCount()));
            writer.write("\n");

            for (int i = 1; i <= m.getRowCount(); i++) {
                for (int j = 1; j <= m.getColCount(); j++) {

                    strForWrite += m.get(i, j) + " ";
                }
                strForWrite += "\n";
            }

            writer.write(strForWrite);
            writer.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (MatrixIndexException e) {
            e.printStackTrace();
        }
    }

    public static Matrix loadMatrixFromFile(String filename) throws FileNotFoundException, IOException {

        try{
            System.out.print("Enter the file name with extension : ");

            Scanner input = new Scanner(System.in);

            File file = new File(input.nextLine());

            input = new Scanner(file);


            while (input.hasNextLine()) {
                String line = input.nextLine();
                System.out.println(line);
            }
            input.close();

        } catch (Exception ex) {
            ex.printStackTrace();
        }
        return null;
    

    }
}