将字符串更改为数组中的double

Question

I am trying to make an Arraylist with its [0] element and [1] element a string and the others doubles. I want to use these arrays for my coordinates in my other classes.

I get an NullPointerException, what am i doing wrong?

enter code here

public class ExampleTextInArrayReader
{
    //naam document van ECG-patiént 1
    public static final String FILE_NAME = "ecg1.txt";
    //array waarin de String van ECG-waarden is omgezet in een ArrayMetDoubles
    private Double[] arrayMetDoubles = new Double[722-2];
    private String[] lines, gegevensPatiënt;
    //velden voor patientnummer en de bijbehorende afdeling
    public void main()
    { 
        // Open the file
        TextInArrayReader in = new TextInArrayReader(FILE_NAME);

        // Check for errors during opening file
        if (in.getError() != null) 
        { 
            System.out.println("Error opening file: " + in.getError());
            System.exit(1);
        }

        // Read the file
        String[] lines = in.getLines();  
        if (in.getError() != null) // check for errors during reading file
        { 
            System.out.println("Error reading file: " + in.getError());
            System.exit(1);
        }

        // Print file contents
        for (int i = 0; i < lines.length; i++) System.out.println(lines[i]);
    }

    public String[] drukGegevensPatiëntAf()
    {
        gegevensPatiënt = new String[2];
        for(int i = 0; i < 2; i++)
        {
            gegevensPatiënt[i] = lines[i];
        }
        return gegevensPatiënt;
    }

    public void changeArray()
    {
        // Get the ECG-values from the lines array and change them in doubles and put them in an arrayMetDoubles array
        arrayMetDoubles = new Double[lines.length - 2];
        for(int i = 2; i < arrayMetDoubles.length; i++)
         {        
            arrayMetDoubles[i] = Double.parseDouble(lines[i + 2]);
        }
    }

    public Double [] getLijnen()
{
    changeArray();
    return arrayMetDoubles;
}

}

Answer 1

Becuase the class member varaible lines is not yet assigned.In the Main method you have assingned to the local variable

 String[] lines = in.getLines(); 

Change the above line to

    lines = in.getLines(); 

in Main() method.

And Make sure the Main() method called before changeArray Method .

Answer 2

I like how you mixed Nederlands with English throughout your code! :)

Anyway, in the for loop, loop from 0 to length-2... Or else the code will fill ArraymetDoubles from index 2 to two places outside the array

public void changeArray()
{

    arrayMetDoubles = new Double[lines.length - 2];
    for(int i = 0; i < arrayMetDoubles.length; i++)
    {        
        arrayMetDoubles[i] = Double.parseDouble(lines[i + 2]);
    }
}