Hi all.I am started to learn game physics and I am trying to move ball with an angle.But it does not change its angle .Java coordinate sydstem is a little different and i think my problem is there.Here my codes

this is for calculating x and y speed

 scale_X= Math.sin(angle);
 scale_Y=Math.cos(angle);
     velosity_X=(speed*scale_X);
 velosity_Y=(speed*scale_Y);

This is for moving ball in run() function

  ball.posX =ball.posX+(int)velosity_X;
  ball.posY=ball.posY+(int)velosity_Y;

I used (int)velosity_X and (int)velosity_Y because in ball class I draw object

g.drawOval(posX, posX, width, height);

and here g.drawOval requares int.I dont know is it problem or not. Also if I use angle 30 it goes +X and +Y but if I use angle 35 it goes -X and -Y. I didnot figure out how work coordinate system on java.