Exception in thread "main" java.lang.NullPointerException 7

Question

(main method calling classes)

import java.io.*;

public class bob {
public static void main(String[] args){
    new bert();
  new larry();

(creates a file and copys string to it)

public class larry{
  bert bertObj = new bert();
  public larry(){
      try{
      File file = new File("text.txt");

      if(!file.exists())
          file.createNewFile();
      PrintWriter pw = new PrintWriter(file);
      for(String x: bertObj.string){
      pw.println(x);
      }
      pw.close();
  }catch(IOException e){
      e.printStackTrace();
  }
  }
}

(reads a file and copies it into a string array) (i havent initialised the string, i think that maybe the error, though i dont know how many values i will be storing inside it so i do not wish to do String string[] = new String[100] for example.... what else can i do?)

public class bert {
  String string[];
  public bert(){
      BufferedReader br = null;
      try{
          br = new BufferedReader(new FileReader("C:\\Program Files\\Java\\jdk1.8.0_101\\THIRDPARTYLICENSEREADME.txt"));
          int counter = 0;
          while((string[counter] = br.readLine()) != null)
          {
              counter++;
          }
          for(int x = counter; x < 4000; x++)
              string[x] = "";
      }catch(IOException e){
          e.printStackTrace();
      }finally{
          try {
              br.close();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  }
}

Answer 1

In class bert, your String[] is never initialized before you try to access it in this line:

while((string[counter] = br.readLine()) != null)

Just like you initialized bert in the larry class, you need to initialize the String[] in the bert class.

Turn this line:

String [] string;

Into:

String[] string = new String[5];  // 5 is an arbitrary number I chose, you need to choose how many strings you will be holding in that array

Sorry, did not fully read your comments. Instead of a static array, try using an arraylist. This does not work the same as an array.

To give you a short example:

ArrayList<String> string = new ArrayList();
string.add("hello");     // string now has a string "hello"
string.add("world");     // string now has a string "hello" followed by a string "world"

for(int i = 0; i < string.size(); i++) {
    System.out.println(string.get(i));  // gets position i from the array and prints it.  Will print hello then a new line then world.
}

More on the arraylist here:

ArrayList API