java - Could not create an object using constructor -

there interface

public interface rtriangle {     int getapexx1();     int getapexy1();     int getapexx2();     int getapexy2();     int getapexx3();     int getapexy3(); } 

and class implement interface

public class righttriangle implements rtriangle{     private point a;     private point b;      private point c;      public righttriangle (int x1, int y1, int x2, int y2, int x3, int y3){         this.a.x=x1;         this.a.y=y1;         this.b.x=x1;         this.b.y=y1;         this.c.x=x1;         this.c.y=y1; }       public int getapexx1(){         return a.x;         }     public int getapexy1(){         return a.y;     }     public int getapexx2() {         return b.x;     }     public int getapexy2(){         return b.y;     }     public int getapexx3(){         return c.x;     }     public int getapexy3(){         return c.y;     } } 

also there class uses class:

public class rtriangleprovider {     public static rtriangle getrtriangle(){         try{             rtriangle tr = new righttriangle(0, 0, 0, 2, 2, 0);             return tr;         }         catch(exception e){             system.out.print(e.tostring());             return null;         }     } } 

and when try use getrtriangle() method i'm getting nullpointerexception exception on line:

 rtriangle tr = new righttriangle(0, 0, 0, 2, 2, 0); 

on righttriangle creation.

public class testtriangle {     @test     public void testright(){         rtriangle tr =rtriangleprovider.getrtriangle();     } } 

i can't understand problem constructor.i appreciate advice.

look @ part:

private point a; ...  public righttriangle (int x1, int y1, int x2, int y2, int x3, int y3){     this.a.x=x1;      ... } 

what expect value of a here? hasn't been set else, null. dereferencing causes exception. suspect want:

public righttriangle (int x1, int y1, int x2, int y2, int x3, int y3){     = new point(x1, y1);     b = new point(x2, y2);     c = new point(x3, y3); } 

also note code uses 6 parameters, whereas original code only uses x1 , y1.

i'd encourage think more in terms of points - rewrite both interface , constructor use point values rather individual x , y values.