Arraylist errors with private fields

[DJRome]

Hi, I'm doing an assignment, and I noticed I keep getting the same error and I don't know how to fix it. I have a set of code that scans in text. I create an object based on said text. But when I try to add these objects to an arraylist of objects that is a private field of that class, it doesn't work.

put it in below. the errors always occur where i try to add to the arraylist field during the while loop. Thanks

public class NameDatabase
{
    // constants
    public static final int MAX_RANK = 1000;
    public static final NameRecord NONE = new NameRecord("Not_Found");

    // name data
    private ArrayList<NameRecord> myNames;


    /**
     * Construct database from file of formatted data.
     */
    public NameDatabase (String filename) throws FileNotFoundException
    {
        // TODO: create myNames and fill it up with data from a file   
    	FileReader reader = new FileReader(filename);
		Scanner in = new Scanner(reader);
		NameRecord nmrd=new NameRecord(in.nextLine());
		System.out.println(nmrd.getName());
		while (in.hasNext()){
			nmrd= new NameRecord(in.nextLine());
			this.myNames.add(nmrd);
			
		}
        
        
    }


    /** 
     * Find a given name within the databasae
     *
     * @param name to find
     * @return data record of matching name or empty record if not found
     */
    public NameRecord match (String name)
    {
        NameRecord result = NONE;
        for (int i=0; i<myNames.size();i++){
        	if (myNames.get(i).getName().equalsIgnoreCase(name)){
        		result=myNames.get(i);
        	}
        }
        

        return result;
    }
}

[RamyaSivakanth]

what error are you getting?

[DJRome]

sorry, the error is
Exception in thread "main" java.lang.NullPointerException
at NameDatabase.<init>(NameDatabase.java:37)
at Main.main(Main.java:26)

here is the main:

public class Main
{
    // constants
    public static final Dimension SIZE = new Dimension(800, 600);
    public static final String TITLE = "Popular Name Surfer";
    public static final String INPUT_PROMPT = "Enter Name to find  ";
    public static final String DATA_FILE = "names-data.txt";
    


    // main --- where the program starts
    public static void main (String args[]) throws FileNotFoundException
    {
        NameDatabase db = new NameDatabase(DATA_FILE);

        // create container to display animations
        Canvas display = new Canvas(SIZE);

        // create user interface controls
        LabelledInput input = new LabelledInput(INPUT_PROMPT, db, display);

        // create container that will work with Window manager
        JFrame frame = new JFrame(TITLE);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        // add our user interface components to Frame and show it
        frame.getContentPane().add(display, BorderLayout.CENTER);
        frame.getContentPane().add(input, BorderLayout.NORTH);
        frame.pack();
        frame.setVisible(true);
    }
}

[JosAH]

You didn't initialize your variabe myNames yet so you probably got a NullPointerException thrown at you.

kind regards,

Jos

[DJRome]

thanks, i got it. but should it be initialized in the fields or in the constructor? im curious to this thanks.

[JosAH]

thanks, i got it. but should it be initialized in the fields or in the constructor? im curious to this thanks.

Well, you should give it a value before you try to use it; you're trying to use it in your constructor so why not define and initialize it in one step? Declare it as follows:

private List<NameRecord> myNames= new ArrayList<NameRecord>();

kind regards,

Jos