protected HSSFCellStyle(short index,
    ExtendedFormatRecord rec,
    HSSFWorkbook workbook) 
{
               
    	this(index, rec, workbook.getWorkbook());
}

Creates new HSSFCellStyle why would you want to do this??

 protected HSSFCellStyle(short index,
    ExtendedFormatRecord rec,
    Workbook workbook) 
{
        this.workbook = workbook;
        this.index = index;
        format     = rec;
}

 public boolean equals(Object obj) 
{
		if (this == obj) return true;
		if (obj == null) return false;
		if (obj instanceof HSSFCellStyle) {
			final HSSFCellStyle other = (HSSFCellStyle) obj;
			if (format == null) {
				if (other.format != null)
					return false;
			} else if (!format.equals(other.format))
				return false;
			if (index != other.index)
				return false;
			return true;
		}
		return false;
}

 public short getAlignment() 
{
        return format.getAlignment();
}

get the type of horizontal alignment for the cell

 public short getBorderBottom() 
{
        return format.getBorderBottom();
}

get the type of border to use for the bottom border of the cell

 public short getBorderLeft() 
{
        return format.getBorderLeft();
}

get the type of border to use for the left border of the cell

 public short getBorderRight() 
{
        return format.getBorderRight();
}

get the type of border to use for the right border of the cell

 public short getBorderTop() 
{
        return format.getBorderTop();
}

get the type of border to use for the top border of the cell

 public short getBottomBorderColor() 
{
        return format.getBottomBorderPaletteIdx();
}

get the color to use for the left border

 public short getDataFormat() 
{
        return format.getFormatIndex();
}

get the index of the format

 public String getDataFormatString() 
{
    	HSSFDataFormat format = new HSSFDataFormat(workbook);
        return format.getFormat(getDataFormat());
}

Get the contents of the format string, by looking up the DataFormat against the bound workbook

 public String getDataFormatString(Workbook workbook) 
{
    	HSSFDataFormat format = new HSSFDataFormat(workbook);
        return format.getFormat(getDataFormat());
}

Get the contents of the format string, by looking up the DataFormat against the supplied workbook

 public short getFillBackgroundColor() 
{
    	short result = format.getFillBackground();
    	//JMH: Do this ridiculous conversion, and let HSSFCellStyle
    	//internally migrate back and forth
    	if (result == (HSSFColor.AUTOMATIC.index+1))
    		return HSSFColor.AUTOMATIC.index;
    	else return result;
}

get the background fill color

 public short getFillForegroundColor() 
{
        return format.getFillForeground();
}

get the foreground fill color

 public short getFillPattern() 
{
        return format.getAdtlFillPattern();
}

get the fill pattern (??) - set to 1 to fill with foreground color

 public HSSFFont getFont(HSSFWorkbook parentWorkbook) 
{
    	return ((HSSFWorkbook) parentWorkbook).getFontAt(getFontIndex());
}

gets the font for this style

 public short getFontIndex() 
{
        return format.getFontIndex();
}

gets the index of the font for this style

 public boolean getHidden() 
{
        return format.isHidden();
}

get whether the cell's using this style are to be hidden

 public short getIndention() 
{
        return format.getIndent();
}

get the number of spaces to indent the text in the cell

 public short getIndex() 
{
        return index;
}

get the index within the HSSFWorkbook (sequence within the collection of ExtnededFormat objects)

 public short getLeftBorderColor() 
{
        return format.getLeftBorderPaletteIdx();
}

get the color to use for the left border

 public boolean getLocked() 
{
        return format.isLocked();
}

get whether the cell's using this style are to be locked

 public short getRightBorderColor() 
{
        return format.getRightBorderPaletteIdx();
}

get the color to use for the left border

 public short getRotation() 
{
      short rotation = format.getRotation();
      if (rotation  > 90)
        //This is actually the 4th quadrant
        rotation = (short)(90-rotation);
      return rotation;
}

get the degree of rotation for the text in the cell

 public short getTopBorderColor() 
{
        return format.getTopBorderPaletteIdx();
}

get the color to use for the top border

 public short getVerticalAlignment() 
{
        return format.getVerticalAlignment();
}

get the type of vertical alignment for the cell

 public boolean getWrapText() 
{
        return format.getWrapText();
}

get whether the text should be wrapped

 public int hashCode() 
{
		final int prime = 31;
		int result = 1;
		result = prime * result + ((format == null) ? 0 : format.hashCode());
		result = prime * result + index;
		return result;
}

 public  void setAlignment(short align) 
{
        format.setIndentNotParentAlignment(true);
        format.setAlignment(align);
}

set the type of horizontal alignment for the cell

 public  void setBorderBottom(short border) 
{
        format.setIndentNotParentBorder(true);
        format.setBorderBottom(border);
}

set the type of border to use for the bottom border of the cell

 public  void setBorderLeft(short border) 
{
        format.setIndentNotParentBorder(true);
        format.setBorderLeft(border);
}

set the type of border to use for the left border of the cell

 public  void setBorderRight(short border) 
{
        format.setIndentNotParentBorder(true);
        format.setBorderRight(border);
}

set the type of border to use for the right border of the cell

 public  void setBorderTop(short border) 
{
        format.setIndentNotParentBorder(true);
        format.setBorderTop(border);
}

set the type of border to use for the top border of the cell

 public  void setBottomBorderColor(short color) 
{
        format.setBottomBorderPaletteIdx(color);
}

set the color to use for the bottom border

 public  void setDataFormat(short fmt) 
{
        format.setFormatIndex(fmt);
}

set the data format (must be a valid format)

 public  void setFillBackgroundColor(short bg) 
{
    	
        format.setFillBackground(bg);
        checkDefaultBackgroundFills();
}

set the background fill color.

For example:

cs.setFillPattern(HSSFCellStyle.FINE_DOTS );
cs.setFillBackgroundColor(new HSSFColor.RED().getIndex());

optionally a Foreground and background fill can be applied: Note: Ensure Foreground color is set prior to background

cs.setFillPattern(HSSFCellStyle.FINE_DOTS );
cs.setFillForegroundColor(new HSSFColor.BLUE().getIndex());
cs.setFillBackgroundColor(new HSSFColor.RED().getIndex());

or, for the special case of SOLID_FILL:

cs.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND );
cs.setFillForegroundColor(new HSSFColor.RED().getIndex());

It is necessary to set the fill style in order for the color to be shown in the cell.

 public  void setFillForegroundColor(short bg) 
{
        format.setFillForeground(bg);
        checkDefaultBackgroundFills();
}

set the foreground fill color Note: Ensure Foreground color is set prior to background color.

 public  void setFillPattern(short fp) 
{
        format.setAdtlFillPattern(fp);
}

setting to one fills the cell with the foreground color... No idea about other values

 public  void setFont(HSSFFont font) 
{
        format.setIndentNotParentFont(true);
        short fontindex = ((HSSFFont) font).getIndex();
        format.setFontIndex(fontindex);
}

set the font for this style

 public  void setHidden(boolean hidden) 
{
        format.setIndentNotParentCellOptions(true);
        format.setHidden(hidden);
}

set the cell's using this style to be hidden

 public  void setIndention(short indent) 
{
        format.setIndent(indent);
}

set the number of spaces to indent the text in the cell

 public  void setLeftBorderColor(short color) 
{
        format.setLeftBorderPaletteIdx(color);
}

set the color to use for the left border

 public  void setLocked(boolean locked) 
{
        format.setIndentNotParentCellOptions(true);
        format.setLocked(locked);
}

set the cell's using this style to be locked

 public  void setRightBorderColor(short color) 
{
        format.setRightBorderPaletteIdx(color);
}

set the color to use for the right border

 public  void setRotation(short rotation) 
{
      if ((rotation <  0)&&(rotation  >= -90)) {
        //Take care of the funny 4th quadrant issue
        //The 4th quadrant (-1 to -90) is stored as (91 to 180)
        rotation = (short)(90 - rotation);
      }
      else if ((rotation <  -90)  ||(rotation  > 90))
        //Do not allow an incorrect rotation to be set
        throw new IllegalArgumentException("The rotation must be between -90 and 90 degrees");
        format.setRotation(rotation);
}

set the degree of rotation for the text in the cell

 public  void setTopBorderColor(short color) 
{
        format.setTopBorderPaletteIdx(color);
}

set the color to use for the top border

 public  void setVerticalAlignment(short align) 
{
        format.setVerticalAlignment(align);
}

set the type of vertical alignment for the cell

 public  void setWrapText(boolean wrapped) 
{
        format.setIndentNotParentAlignment(true);
        format.setWrapText(wrapped);
}

set whether the text should be wrapped