java - Painting balloons on Graphics2D -

i want make bubble shooter game , have problem generate bubbles @ start. when trying compile program, have error: exception in thread "awt-eventqueue-0" java.lang.nullpointerexception.

public class mypanel extends jpanel {     init init;      public mypanel(){         super();         init = new init();           }      public void paint(graphics g){         dimension size = getsize();         graphics2d g2d = (graphics2d) g;         g2d.setcolor(color.gray);         g2d.fillrect(0, 0, size.width, size.height - 70);         for(int j = 0; j < 10; j++)             for(int = 0; < 20; i++){                 init.fields[i][j].b.paint(g);       //here compiler shows error             }     } }   public class field {     private int x;     private int y;     private int r = 30;     public baloon b;       public field(int x, int y){         this.x = x*r;         this.y = y*r;     }      public void addbaloon(int n){         b = new baloon(this.x, this.y, r, n);         } }  public class init {      parser pr = new parser();     private int r = pr.getradius();     private int x = pr.getxdimension();     private int y = pr.getydimension();     private int ni = pr.getcolorrange();      field[][] fields = new field[x][y];      private int startx = 20;     private int starty = 10;      public init(){         for(int yi = 1; yi<y; yi++){             (int xi = 1; xi<x; xi++){                 fields[xi][yi] = new field(xi*r, yi*r);                      }         }          for(int yi = 1; yi < starty; yi ++){             for(int xi = 1 ; xi < startx; xi++){                 random rand = new random();                 int n = rand.nextint(ni);                 fields[xi][yi].addbaloon(n);                 }         }            } } 

you initializing array index 1:

for(int yi = 1; yi<y; yi++){     (int xi = 1; xi<x; xi++){         fields[xi][yi] = new field(xi*r, yi*r);              } } 

while accessing 0 like:

for(int j = 0; j < 10; j++)     for(int = 0; < 20; i++){         init.fields[i][j].b.paint(g);       //here compiler shows error     } 

array index starts 0 , goes upto n-1. need initialize like:

for(int yi = 0; yi<y; yi++){     (int xi = 0; xi<x; xi++){         fields[xi][yi] = new field(xi*r, yi*r);              } }