Two Parts to Recursion

I can't allow a chapter to go by without reminding you of this: A recursive definition has two parts:

1. If the problem is easy, solve it immediately.
2. If the problem can't be solved immediately, divide it into smaller problems, then:
   • Solve the smaller problems by applying this procedure to each of them.

Our seriously wrong drawStar() method does not test for a base case. Look at it again:

 
  // Grievously Awful Method
  //
  private void drawStar( int x, int y, int size )
  {
    int endX, endY ;
     
    // Six lines radiating from (x,y)
    for ( int i = 0; i<6; i++ )
    {
      endX = x + (int)(size*Math.cos( (2*Math.PI/6)*i ));
      endY = y - (int)(size*Math.sin( (2*Math.PI/6)*i ));
      graph.drawLine( x, y, endX, endY );
      drawStar( endX, endY, size/3 ) ;
    }
  }