private void validateHeight() {
        
        boolean error = false;
        heightError.setText("");
                
        String heightInput = height.getText();
        if("".equals(heightInput))
        {
            error = true;
            heightError.setText("*the input cannot be empty!");
        }
        else
        {
            try {
            boxHeight = Double.parseDouble(heightInput);
            }
            catch (Exception e) 
            {
             //System.err.println(e);
             error = true;
             heightError.setText("*the height must be a float number!");
            }
        }
        if(error == false)
        {
            if(boxHeight < minHeight)
            {
                heightError.setText("*the height value must be greater than or equal with "+minHeight+" "+unitMeasure);
            }
            else
            if(boxHeight > maxHeight)
            {
                heightError.setText("*the height value must be less than or equal with "+maxHeight+" "+unitMeasure);
            }
        }
    }