cannot understand the exception in my code,please help

[liu hao]

the null Point exception occurs at the at

 MyRectangle.setBottomLeftPoint.

but I think my constructor has initialized the point2D objects.
please point out my mistake. tons of thanks.

import java.util.*;
import java.awt.geom.Point2D;

public class MyRectangle {

   // Data members: the two corner points
   private Point2D.Double bottomLeftPoint;
   private Point2D.Double topRightPoint;
   
   // Constructor
   public MyRectangle(Point2D.Double pt1, Point2D.Double pt2) {
      setBottomLeftPoint(pt1);
      setTopRightPoint(pt2);
   }
   
//---------------------------------------------------------------
// Methods:
//  (Each method should be preceded by a line of description.)
//  (You may create additional methods of your own.)
//---------------------------------------------------------------
   //to set the bottom point of the rectangle
   public void setBottomLeftPoint (Point2D.Double pt) {
     bottomLeftPoint.setLocation(pt.getX(),pt.getY());
   }
 
   //to set the top point 
   public void setTopRightPoint (Point2D.Double pt) {
     topRightPoint.setLocation(pt.getX(),pt.getY());
   }

   //to get the bottom point
   public Point2D.Double getBottomLeftPoint () {
     return this.bottomLeftPoint;
   }

   //to get the top point
   public Point2D.Double getTopRightPoint () {
      return this.topRightPoint;
   }
  
   //to print the rectangle literally 
   public String toString() {
     return "("+topRightPoint.toString()+"; "+bottomLeftPoint+" )";
   }

   public static int isOverlap(MyRectangle recA,MyRectangle recB){
     final int DISJOINT=0,ADJACENT=1,OVERLAP=2;
     double _1y1=recA.topRightPoint.getY();
     double _1y2=recA.bottomLeftPoint.getY();
     double _2y1=recB.topRightPoint.getY();
     double _2y2=recB.bottomLeftPoint.getY();
     if((Math.abs((_1y1+_1y2)/2-(_2y1+_2y2)/2)>Math.abs(_1y1-_1y2)/2+Math.abs(_2y1-_2y2)/2))
     return DISJOINT;
     if((Math.abs((_1y1+_1y2)/2-(_2y1+_2y2)/2)==Math.abs(_1y1-_1y2)/2+Math.abs(_2y1-_2y2)/2)) 
     return ADJACENT;  
     else
     return OVERLAP;  
   }
     public static double select(double a,double b,double c,double d ){
     double[] list={a,b,c,d};
     Arrays.sort(list);
     return list[2]-list[1];
}
   public static double commonArea(MyRectangle recA,MyRectangle recB){
     double deltaX=select(recA.topRightPoint.getX(),recA.bottomLeftPoint.getX(),recB.topRightPoint.getX(),recB.bottomLeftPoint.getX());
     double deltaY=select(recA.topRightPoint.getY(),recA.bottomLeftPoint.getY(),recB.topRightPoint.getY(),recB.bottomLeftPoint.getY());
     return deltaX*deltaY;
   }
   //    /-----------------------------------------------------
   // main method to test the MyRectangle class
   //-----------------------------------------------------
   public static void main (String[] args)  {

      Scanner scanner = new Scanner(System.in);
      Point2D.Double pt1,pt2;
      pt1=new Point2D.Double(scanner.nextDouble(),scanner.nextDouble());
      pt2=new Point2D.Double(scanner.nextDouble(),scanner.nextDouble());
      System.out.println(pt1);
       System.out.println(pt1);
      MyRectangle rectangleA= new MyRectangle(pt1,pt2);
      pt1=new Point2D.Double(scanner.nextDouble(),scanner.nextDouble());
      pt2=new Point2D.Double(scanner.nextDouble(),scanner.nextDouble());
      MyRectangle rectangleB= new MyRectangle(pt1,pt2); 
      System.out.println(rectangleA);
      System.out.println(rectangleB);                                        
      int i=isOverlap(rectangleA,rectangleB);
      switch(i){
        case 0 :System.out.println("rectangle A and B are disjoint");
                break;
        case 1: System.out.println("rectangle A and B touch each other");
                break;
        case 2: System.out.println("rectangle A and B overlap each other");
                System.out.println("overlaped area = "+commonArea(rectangleA,rectangleB));
      }
   }
}
    

[Seetharaman Venkatasamy]

liu hao wrote:the null Point exception occurs at the at

 MyRectangle.setBottomLeftPoint.

in which line you invoking this ? instead please tell the line number

[D. Ogranos]

You are never initialising the Point2D objects in your MyRectangle class. In your constructor (or in the declaration) you need to create new objects for these. For example, your method setBottomLeftPoint attempts to do something like null.setLocation(...).

OR, simply assign the Point2D objects that you are passing to your constructor to your instance variables.

[liu hao]

a lot of thanks.It seems I didn't understand that staff thoroughly.

[Campbell Ritchie]

And welcome to JavaRanch