为什么我会收到 OutOfBoundsException

这是因为默认lineCount值初始化为零，然后您创建一个长度为零的数组：

Point[] points = new Point[lineCount];

创建数组后，输入值lineCount。

试试这样：

public class Point {
    private int lineCount;
    private final int x;
    private final int y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    Point[] points;

    public void pointsCreator() {
        Scanner scanner = new Scanner(System.in);
        lineCount = scanner.nextInt();

        points = new Point[lineCount];

        System.out.println("----------------------");
        System.out.println("enter points for first line: ");
        points[0] = pointFiller(scanner);

        for (int i = 1; i < lineCount; i++){
            System.out.println("----------------------");
            System.out.println("enter points for next line:");
            points[i] = pointFiller(scanner);
        }

        System.out.println("----------------------");
        System.out.println(Arrays.toString(points));
    }

    public static Point pointFiller(Scanner scanner) {
        System.out.print("     - enter x: ");
        int x = scanner.nextInt();

        System.out.print("     - enter y: ");
        int y = scanner.nextInt();

        return new Point(x, y);
    }

    @Override
    public String toString() {
        return "Points for line {x = " + x + ", y = " + y + '}';
    }
}

Point[] points = new Point[lineCount];

执行此行时，lineCount == 0. 在那之后，你在逻辑上离开了数组，因为 该数组的长度为零。

lineCount从控制台获取值后初始化数组。