为什么我无法在 Java 中访问 Point2D 的数据字段？

Question

I want to create an array of 100 random points using Point2D. But why can't I access its data field while the data field of Point2D is public? It said "x cannot be resolved or not a field."

public static void main(String[] args) {
            
    Point2D[] points = new Point2D.Double[100];
    for (int i = 0; i < points.length; i++) {
        points[i] = new Point2D.Double();
        points[i].x = Math.random() * 100;
        points[i].y = Math.random() * 100;
    }
}

Answer 1

You might want to use setLocation . The error-message just says that the compiler doesn't know what .x is supposed to mean on an object of type Point2D.

Answer 2

In your code, points has type Point2D[] , therefore points[i] has type Point2D . Point2D does not have members named x or y . The fact that at runtime the class of points[i] happens to be Point2D.Double , which does have such members, is irrelevant to the compiler's analysis.

You could instead declare points as

    Point2D.Double[] points = new Point2D.Double[100];

, or you could use Point2D.setLocation() instead of assigning to member variables, as your other answer already suggests.