如何从另一个类读取数组与数组的副本？ [正在加载文件]

Question

I want to create a game and I need to read file from the notepad when I use my loadfile.java alone, it work very well. Then, I would like to copy my data into datafile.java as it will be easier for me to do the fighting scene. However, I can't copy the array in my loadfile.java to the datafile.java and I don't understand why.

import javax.swing.*;
import java.io.*;
import java.util.Scanner;

public class loadfile 
{
   static String filename = "Save.txt";
   static int size = 4;
   static int s;
   static int[] number;
   static String[] line;

   private static void load() throws IOException
   {
      BufferedReader reader = new BufferedReader(new FileReader(filename));
      while (reader.readLine()!= null)
      {
         size++;
      }
      size -= 4;
      reader.close();

      line = new String[size];
      number = new int[size];
      BufferedReader reader2 = new BufferedReader(new FileReader(filename));

      for (int i = 0; i < size; i++)
      {
         line[i] = reader2.readLine();
      }

      reader2.close();

      for (int i = 4; i < size; i++)
      {
         number[i] = Integer.parseInt(line[i]);
      }

   }

   public static String[] getData()
   {
      return line;
   }   

   public static int[] getNumber()
   {
      s = size - 4;
      int[] num = new int[s];
      for (int i = 0; i < s; i++)
      {
         num[i] = number[i+4];
      }
      return num;
   }

   public static int getDataSize()
   {
      return size;
   }

   public static int getNumberSize()
   {
      return size - 4;
   }

This is my loadfile.java I use the file with 4 names and 9 * n int in the notepad as I want to check whether I have the character first before I read the file. However, before I can handle this problem, I got another problem that I can't copy the array into my datafile.java

The datafile.java is separate with two constructor. One is for Starting the game and one is for loading the data. The constructor with the (int num) is the problem I have. First, I would like to show the java first:

import java.util.Arrays;
import java.io.*;
public class datafile
{
   private static String[] data;
   private static int[] number;
   private static String[] name;
   private static int[] a, d, s;
   private static int[] hp, maxhp;
   private static int[] mp, maxmp;
   private static int[] lv, exp;

   public datafile()
   {
      initialization();
      name[0] = "Pet";
      a[0] = 100;
      d[0] = 100;
      s[0] = 100;
      hp[0] = 500;
      mp[0] = 500;
      maxhp[0] = 500;
      maxmp[0] = 500;
      exp[0] = 100;
      lv[0] = 1;    
   }

   public datafile(int num) throws IOException
   {
      initialization();
      loadfile l = new loadfile();
      for (int i = 0; i < l.getNumberSize(); i++)
      {
         number[i] = l.getNumber()[i];
      }
      for (int i = 0; i < l.getDataSize(); i++)
      {
         data[i] = l.getData()[i];
      }
      for(int i = 0; i < 4; i++)
      {
         name[i] = data[i];
      }

      for(int i = 0; i < 4; i++)
      {
         a[i] = number[1+(i*9)];
         d[i] = number[2+(i*9)];
         s[i] = number[3+(i*9)];
         hp[i] = number[4+(i*9)];
         mp[i] = number[5+(i*9)];
         maxhp[i] = number[6+(i*9)];
         maxmp[i] = number[7+(i*9)];
         lv[i] = number[8+(i*9)];
         exp[i] = number[9+(i*9)];
      }

   }   

   public static String getName(int n)
   {
      return name[n];
   }

   public static int getAttack(int n)
   {
      return a[n];
   }

   public static int getDefense(int n)
   {
      return d[n];
   }

   public void initialization()
   {
      name = new String[3];
      a = new int[3];
      d = new int[3];
      s = new int[3];
      hp = new int[3];
      mp = new int[3];
      maxhp = new int[3];   
      maxmp = new int[3];
      lv = new int[3];
      exp = new int[3];   
   }

   public static void main (String[] args) throws IOException

   {
      new datafile(1);
   }
}

When I run the program, the debugging state this line

data[i] = l.getData()[i];

as an error

I don't know what wrong with this line and I tried so many different ways to change the way the copy the method. However, it didn't work

The error says this:

Exception in thread "main" java.lang.NullPointerException
    at datafile.<init>(datafile.java:38)
    at datafile.main(datafile.java:92)

I hope you guys can help me with this problem because I don't want to fail with my first work

Answer 1

in your datafile(int num) you call

loadfile l = new loadfile();

but you never call the load() method on you loadfile

l.load();

Answer 2

Edit: my bad, I didn't see your initialization method, but regardless, I'm going to stick with my recommendation that you radically change your program design. Your code consists of a kludge -- you've got many strangely named static array variables as some kind of data repository, and this suggests that injecting a little object-oriented design could go a long way towards creating classes that are much easier to debug, maintain and enhance:

First I recommend that you get rid of all of the parallel arrays and instead create a class, or likely classes, to hold the fields that need to be bound together and create an ArrayList of items of this class.

For example

public class Creature {
   private String name;
   private int attack;
   private int defense; 

   // constructors here

   // getters and setters...
}

And elsewhere:

private List<Creature> creatureList = new ArrayList<>();

Note that the Creature class, the repository for some of your data, should not be calling or even have knowledge of the code that loads the data, but rather it should be the other way around. The class that loads data should create MyData objects that can then be placed within the myDataList ArrayList via its add(...) method.

As a side recommendation, to help us now and to help yourself in the future, please edit your code and change your variable names to conform with Java naming conventions: class names all start with an upper-case letter and method/variable names with a lower-case letter.