ArrayList x，y坐标距离计算

Question

Can anyone help me figure out how to make this calculation work? I keep working myself in circles and I honestly don't know what to do. This is my current file that I'm working on:

import java.util.*;
import java.io.*;

public class Assignment_12 {

   public static void main (String[] args) {
      Scanner input = new Scanner(System.in);    

      System.out.println("name goes here");
      System.out.println("You may quit at any time by typing \"Q\".");
      ArrayList<Double> numbers = new ArrayList<Double>();
      ArrayList<Double> numbers2 = new ArrayList<Double>();
      System.out.println("Please enter an X coordinate: ");
      //Point pnt = new Point();

      while (input.hasNextDouble()) {
         numbers.add(input.nextDouble());
         System.out.println("Please enter a Y coordinate: ");
         numbers2.add(input.nextDouble());

         double x = (double) numbers.get(0);
         double y = (double) numbers2.get(0);

         Point pnt = new Point(x, y);
         System.out.println(pnt.getX()); // just to make sure the "object created"?
         System.out.println(pnt.getY()); // same as before, I think
         System.out.println(pnt.distance(pnt.getX(), pnt.getY())); // how to calculate??
      }

      if (input.equals("Q")){
         System.exit(0);
      }
   }
}

And this is the class that I'm just trying to figure out how to make the actual actual calculation work:

public class Point {

   private double x;
   private double y;

   public Point(){
      this.x = 0.0;
      this.y = 0.0;
   }

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

   public double distance(Point pt){
      return Math.sqrt((x - pt.x)*(x - pt.x) + (y - pt.y)*(y - pt.y));
   }

   public double getX(){
      return x;
   }

   public double getY(){
      return y;
   }
}

I'm truly struggling on what exactly to do. I seemingly created the pnt object with x and y , but I don't necessarily understand how to make the calculated distance be available to print. I have tried System.out.println(pnt.distance(pnt.getX(), pnt.getY())); and other similar things, but I'm just stumped. Any advice would be greatly appreciated!

Answer 1

Take a careful look at the signature of your method:

double distance(Point pt)
//              ⬑ single parameter of type Point

This method is called on a Point , which you did correctly with point.distance(... . But it takes one parameter, which also is of type Point . You didn't pass a Point though. Let me rephrase your code a little:

double someX = pnt.getX();
double someY = pnt.getY();
pnt.distance(someX, someY)

This can't work, as you pass two double , instead of one Point . So what you can do is:

pnt.distance(pnt)
//           ⬑ single parameter of type Point

Compare this to what you did:

pnt.distance(pnt.getX(), pnt.getY())
//           ⬑          ⬑ two parameters of type double

But let me point out that this will return 0 , as you just calculated a Point s distance to itself. Try:

Point otherPnt = new Point(13, 8.5);
System.out.println(pnt.distance(otherPnt));

Which will return at least a somewhat more interesting result.