Illegal Argument Exception

Question

I am working on a really simple point class but I am getting an error and I can't pinpoint where the String/double problem is happening or how to fix it.

public String getDistance (double x1,double x2,double y1,double y2) {

            double X= Math.pow((x2-x1),2); 
            double Y= Math.pow((y2-y1),2); 

            double distance = Math.sqrt(X + Y); 
            DecimalFormat df = new DecimalFormat("#.#####");

            String pointsDistance = (""+ distance);

             pointsDistance= df.format(pointsDistance);

            return pointsDistance;
        }

and the test code

double x1=p1.getX(),
                       x2=p2.getX(), 
                       y1=p1.getY(),
                       y2=p2.getY(); 

           pointsDistance= p1.getDistance(x1,x2,y1,y2);

EDIT

I forgot to add the error I'm receiving:

Exception in thread "main" java.lang.IllegalArgumentException: Cannot format given Object as a Number
at java.text.DecimalFormat.format(Unknown Source)
at java.text.Format.format(Unknown Source)
at Point.getDistance(Point.java:41)
at PointTest.main(PointTest.java:35)

Answer 1

You passed a String, but the format method expects a double and returns a String. Change from

String pointsDistance = (""+ distance);
pointsDistance= df.format(pointsDistance);

to

String pointsDistance = df.format(distance);

Answer 2

Replace this:

String pointsDistance = (""+ distance);

pointsDistance= df.format(pointsDistance);

with:

String pointsDistance = df.format(distance);

The problem is that your number format doesn't accept a string.