为什么我不能使用 java.awt.geom.Point2D 中的距离方法？

Question

I can't use distance() from Point2D. Please help me fix my code, thank you!

import java.util.Scanner;

import java.awt.geom.Point2D.Double;

public class TestPoint2D {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        System.out.print("Enter point 1");
        double x1 = input.nextDouble();
        double y1 = input.nextDouble();
        
        System.out.print("Enter point 2");
        double x2 = input.nextDouble();
        double y2 = input.nextDouble();
        
        Point2D p1 = new Point2D(x1, y1);
        Point2D p2 = new Point2D(x2, y2);
        System.out.println(p1.distance(p2));
    }
}

Answer 1

As Point2D docs say:

This class is only the abstract superclass for all objects that store a 2D coordinate. The actual storage representation of the coordinates is left to the subclass.

So you need to use Point2D.Double or Point2D.Float to initialize the object.

So this code to initialize Point2D works:

Point2D p1 = new Point2D.Double(x1, y1);
Point2D p2 = new Point2D.Double(x2, y2);

This "problem" is because Point2D is an abtract class. You can check here how works if you have doubts. But, to associate it with the "Point2D problem", check the first paragraphs and you will understand better.

Abstract class : is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class).

That's exactly the problem (cannot create objects) and the solution (inherit from another class)