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Thread: reading files

  1. #26
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    Default Re: 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.

  2. #27
    Super Moderator Norm's Avatar
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    Default Re: reading files

    No I do not know what value has the NULL value.
    Then you need to find it.
    How many variables are on line 37?
    Add a println() statement just before line 37 that prints out the values of ALL the variables used on line 37 so you can see which variable is null.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #28
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    Default Re: reading files

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

  4. #29
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    Default Re: reading files

    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

  5. #30
    Super Moderator Norm's Avatar
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    Default Re: reading files

    Glad you got it working.
    If you don't understand my answer, don't ignore it, ask a question.

  6. #31
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    Default Re: reading files

    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.

  7. #32
    Super Moderator Norm's Avatar
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    Default Re: reading files

    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)
    The String: "PETER" can not be converted to an int (using a normal radix).

    I am trying to convert a string to a int.
    It will work better if the String only contains numeric digits: 0 to 9

    use the [] operator
    That operator is for arrays, not ArrayLists.
    Use a method like get() to access the contents of an object like an ArrayList
    If you don't understand my answer, don't ignore it, ask a question.

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