Java, using an array of points

Question

I am writing a program in Java, in which I define a class

class Point
{
    double x;
    double y;
}

Then in a method, I define an array of points, as follows:

Point[]     line = new Point[6];

In the same method, I have the line

line[SampleSize - i + 1].x = i;

The first time this statement is hit, the value of its array index is 1; but the program throws a null pointer exception at this point.

This would seem like the correct way to index the field of an object within an array of objects. What am I doing wrong?

Thanks in advance for any suggestions.

John Doner

Answer 1

You have to initialize the value before accessing it:

line[SampleSize - i + 1] = new Point();

Answer 2

That's because you have not created the points to put in the array

for (int index = 0; index < line.length; index++)
{
    line[index] = new Point();
}