Thread: reading files

No I do not know what value has the NULL value. I created a ArrayList twice, an int and string, set them a private. Later I used them on line 38 or 37. I took in the value from the scanner and that is where the error is.

Just on a sidenote, you never create any ArrayList objects in your code. So I guess the NPE probably has to do with that.

import java.io.*;
import java.util.ArrayList;
import java.util.Formatter;
import java.util.Scanner;
 
 
public class read_file 
{
	private Formatter make_file;
	private ArrayList<String>names;
	private int counter;
	private ArrayList<Integer>age;
 
	// error saysjava.lang.NullPointerException, java.lang.NullPointerException
	//at read_file.FileInput(read_file.java:37)
	//at read_file.main(read_file.java:56)
 
	//tried to make a constructor and create new string objects but this doesn't work either.
	public read_file(){ } 
 
	void FileInput()
	{
		File input = new File("example.txt");
 
		if(!input.exists())
		{
			try{make_file = new Formatter("example.txt");System.out.println("A file had to be made, named "+input);}
			catch(IOException e){System.out.println("File was unable to be made");}
		}
		else
		{
			try 
			{
			Scanner reader = new Scanner(new FileInputStream(input));
			names = new ArrayList<String>();
			age = new ArrayList<Integer>();
 
			while(reader.hasNextLine())
			{
				names.add(reader.next());
				age.add(reader.nextInt());
				counter++;	
			}
			reader.close();
			}catch(Exception e){System.out.println("The file could not be read "+e);e.printStackTrace();}
		}
	}
 
	void PrintFile()
	{
 
		for(int i=0;i<counter;i++){System.out.println(names.get(i)+" "+age.get(i));}
	}
 
	public static void main(String[] args)
	{
		read_file r = new read_file();
 
		r.FileInput();
		r.PrintFile();
	}
}

Thanks for putting up with me Norm

I am picking up what you were putting down, it works

void PrintFile()
	{
 
		for(int i=0;i<counter;i++)
		{
			System.out.println(names.get(i)+" "+age.get(i));
		}
 
		for(int j=0; j<counter; j++)
		{
			int value = Integer.parseInt(names.get(j));
 
			System.out.println("The integer value of this string is: "+value);
		}
	}

I am continuing to try new things and just experiment and I am getting the following errors:

Exception in thread "main" java.lang.NumberFormatException: For input string: "PETER"
at java.lang.NumberFormatException.forInputString(Num berFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:449)
at java.lang.Integer.parseInt(Integer.java:499)
at read_file.PrintFile(read_file.java:58)
at read_file.main(read_file.java:69)

I am trying to convert a string to a int.

At first I wanted to simply use the [] operator in a loop for each char while taking the (int) value of it and adding it (+=) to a variable.
I guess ArrayList does not quite work that way.