save mouse clicks in java

I am trying to save the location of the mouse position-on a click.Then i need to analyze its motion to do a specific task.I used the mouseListener interface and when the user clicks the mouse i add the point of clicking to a point array.Then when a user clicks on a button,i tried loop through the array to analyze the motion but i g开发者_运维问答et a null pointer exception at if(points[i].x<points[i+1].x) Here is the code

Point points[] = new Point[2000];
int numPoints = 0;
void eventOutput(String eventDescription, MouseEvent e) {
  System.out.println(eventDescription+" X= "+e.getX()+" Y= "+e.getY());
  //xList.add(new Integer(e.getX()));
  //yList.add(new Integer(e.getY()));
  points[numPoints] = new Point(e.getX(), e.getY());
  ++numPoints;        
}
for(int i=0;i<points.length;i++)
{
  System.out.println("In MOO "+points[i].x);
  if(points[i].x<points[i+1].x)
  {
    xInc=true;
    if(points[i].y<points[i+1].y)
    {
      yInc=true;
    }
    else if(points[i].y>points[i+1].y)
    {
      yDec=true;
    }
  }
  else if(points[i].x>points[i+1].x)
  {
    xDec=true;
    if(points[i].y<points[i+1].y)
    {
      yInc=true;
    }
    else if(points[i].y>points[i+1].y)
    {
      yDec=true;
    }}}}

Could anyone please help me about that.Thanks in advance

You don't want to loop over all of the array -- you only want to loop up to numPoints, since later entries are null, right? In fact, if you're going to compare an element with the next element, then you actually only want to loop up to i < numPoints-1, so that you have one more at the end to compare with.

Consider using a List like an ArrayList rather than an array -- it would be easier to avoid problems like this.

you must iterate up to numPoints instead of points.length at

for(int i=0;i<points.length;i++)

points.length is total size of array, not the number of elements that contains.