also: a processing sketch can't just transferred 1:1 into an eclipse project.

see:  http://processing.org/learning/eclipse/

The for loop limit is off be 1

for ( int  i=0;i< npoints ;i++){

maybe should be

for ( int  i=0;i< npoints-1 ;i++){

--------------------------------------------

npoints is wrong

--------------------------------------

the allocation of  points[] is incorrect.

--------------------------------------

Add 

println("i= " + i);

inside the for loop and see how far you get.

1. Failing at i=0 is an allocation problem

2. Failing when i equals npoints is a bounds problem.

3. Failing at some other value will provide a clue that the allocation does not match npoints.

 /*try

{beginShape();

}

 

 

 

The error is thrown by beginShape();

 

at processing.core.PApplet.beginShape(Unknown Source)

at Voronoi.Polygon.render(Polygon.java:83)

at processing.core.PApplet.handleDraw(Unknown Source)

at processing.core.PApplet.run(Unknown Source)

at java.lang.Thread.run(Unknown Source)

 

 

nope :(

 

Follwing are the three classes, ie three java files trial, polygon, points

 

 

import processing.core.PApplet;
public class trial extends PApplet{
 
 public void setup(){
 }
 public void draw ()
 {  render();
 }
 
 void render(){

 Point []pts=new Point[4];
 if(pts!=null)
 {pts[0]=new Point(30,20,0);
 pts[1]=new Point(85,20,0);
 pts[2]=new Point(85,75,0);
 pts[3]=new Point(20,75,0);
 }
 
 Polygon boundary=new Polygon(pts);
 boundary.render();
  }

}

............................................................................................................................

 

//------ POLYGON ------//

import processing.core.PApplet;

 

public class Polygon extends PApplet{
 
  Point[] points = new Point[1000];
   Polygon(Point[] $points){
    this.points=$points;
}
 
 
  void render(){
   for(int i=0;i<4;i++){
    System.out.println(points[i].x);
   }
 beginShape();
  
    if(points!=null)
    for(int i=0;i<4;i++){
      vertex(points[i].x,points[i].y,points[i].z);
      System.out.println(points[i].x);
    }
    endShape(CLOSE);
   
   
  }
}

................................................................................................................................................

 

 

 

//------ POINT ------//

import processing.core.PApplet;

public class Point {
  int n;
  float x,y,z;
  Point(float $x,float $y,float $z){
   
    x =  $x;
    y =  $y;
    z =  $z;
  }
 
 
 
}

Any ideas?

thank you everyone