I made a SimpleGeometricObject class, a Point class that finds the distance betw

Question

I made a SimpleGeometricObject class, a Point class that finds the distance between two points, and a TriangleFromSimpleGeometricObject class that is a subclass to find the area and perimeter of a triangle given three points. However, my test program isn't working. I'm getting this response after running it: Exception in thread "main" java.lang.NullPointerException
at TriangleFromSimpleGeometricObject.<init>(TriangleFromSimpleGeometricObject.java:42)
at TestTriangle.main(TestTriangle.java:18).

Here is Point:

public class Point {

private double x;
private double y;


public Point ()
{
  
}

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

public double getX()
{
  return x;
}

public double getY()
{
  return y;
}

public double getDistance(Point PointB)
{
  double x2 = PointB.getX();
  double y2 = PointB.getY();
  
  double part1 = (x2 - x)*(x2 - x);
  double part2 = (y2 - y)*(y2 - y);
  
  return Math.sqrt((part1) + (part2));
  
  
}
// Point Point1 = new Point(1,1);
// Point Point2 = new Point(0,0);
// System.out.println(Point1.getDistance(Point2));

}

Here is TriangleFromSimpleGeometricObject:

public class TriangleFromSimpleGeometricObject
  extends SimpleGeometricObject {
  
private Point A;
private Point B;
private Point C;

public TriangleFromSimpleGeometricObject()
{
  
}

public TriangleFromSimpleGeometricObject(Point a, Point b, Point c)
{
  this.A = a;
  this.B = b;
  this.C = c;
}

//* Return point A
public Point getA()
{
  return A;
}

//* Return point B
public Point getB()
{
  return B;
}
//* Return point C
public Point getC()
{
  return C;
}

//* Get side lengths
   public double getDistance(Point a, Point b)
   {
  
   }

double LengthA = A.getDistance(B);
double LengthB = B.getDistance(C);
double LengthC = C.getDistance(A);


  
//*getArea

public double getArea()
{
  double Semi = (LengthA + LengthB + LengthC)/2;
  double Area = Math.sqrt((Semi)*(Semi - LengthA)*(Semi - LengthB)*(Semi - LengthC));
  return Area;
}

//*Get Perimeter
public double getPerimeter()
{
  double Perimeter = LengthA + LengthB + LengthC;
  return Perimeter;
}

  public String toString()
{
  return "The triangle was created on " + getDateCreated() + " with the points " + A + " " + B + " "+ C;
}
}

Here is TestTriangle:

public class TestTriangle
{
public static void main(String[] args)
{
  
  //*(1,3), (-2,-2), (3,-1)
  double x1 = 1;
  double y1 = 3;
  double x2 = -2;
  double y2 = -2;
  double x3 = 3;
  double y3 = -1;
  Point A = new Point(x1, y1);
  Point B = new Point(x2, y2);
  Point C = new Point(x3, y3);
  TriangleFromSimpleGeometricObject triangle = new TriangleFromSimpleGeometricObject(A, B, C);
  
  System.out.println(triangle.toString());
  System.out.println("The area is " + triangle.getArea() + ".");
  System.out.println("The perimeter is " + triangle.getPerimeter() + ".");
  
  
}
}

Thanks!

.

Explanation / Answer

You are getting errors because

1) TriangleFromSimpleGeometricObject.<init>(TriangleFromSimpleGeometricObject.java:42)

//* Get side lengths
public double getDistance(Point a, Point b)
{

}

This is the code present at the line 42. Here the method is returing double but there is no return statement of double variable or value.

Solution:

Do all the required calculations required using the two objects a and b. Then return some double value will resolves this problem.

2. TestTriangle.main(TestTriangle.java:18).

System.out.println(triangle.toString());

This is line present on line 10. Here you are trying to invoke the toString method.

Solution:

To execute the toString code just include only the object name. So the statement should be like

System.out.println(triangle);

**Again in the toString method of TriangleFromSimpleGeometricObject class you have included a method called getDateCreated which is not implemented in any class. Make sure that you implement this method.

**Comment for any furthur queries

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