public GridLayout (int rows, int cols, int hgap, int vgap)
public GridLayout ()
  public GridLayout (int rows, int cols, int hgap, int vgap)  {    if (rows < 0)      throw new IllegalArgumentException ("number of rows cannot be negative");    if (cols < 0)      throw new IllegalArgumentException ("number of columns cannot be negative");    if (rows == 0 && cols == 0)      throw new IllegalArgumentException ("both rows and columns cannot be 0");    if (hgap < 0)      throw new IllegalArgumentException ("horizontal gap must be nonnegative");    if (vgap < 0)      throw new IllegalArgumentException ("vertical gap must be nonnegative");    this.rows = rows;    this.cols = cols;    this.hgap = hgap;    this.vgap = vgap;  }