change text of slide in java using aspose api ppt

Question

public void save()
{ Presentation pres = new Presentation(filename);

ISlide slide = pres.getSlides().get_Item(0);

IShape shape= null;


for (int i = 0 ; i < slide.getShapes().size() ; i++)
{    shape = slide.getShapes().get_Item(i);
if (shape.getPlaceholder() != null)
{
((IAutoShape)shape).getTextFrame().setText(txtArea.getText());
}
}


pres.save(filename,SaveFormat.Ppt);

}

This code is for changing the text but it's not working. I have used two APIs at a time, display code is below:

public void Display(int currentPage, String source)
    {
        try {
        // Create a slideshow object; this creates an underlying POIFSFileSystem object for us
        SlideShow ppt = new SlideShow(new HSLFSlideShow(source));
        current=currentPage;
        // Get all of the slides from the PPT file
        Slide[] slides = ppt.getSlides();
        Dimension pgsize = ppt.getPageSize();
        all = slides.length;
        String temp="";
        lblPage.setText(currentPage+" / "+all);

            BufferedImage img = new BufferedImage(pgsize.width, pgsize.height, BufferedImage.TYPE_INT_RGB);
            Graphics2D graphics = img.createGraphics();
graphics.setPaint(Color.white);
graphics.fill(new Rectangle2D.Float(0, 0, pgsize.width, pgsize.height));

//render
slides[currentPage-1].draw(graphics);
//save the output
            /*FileOutputStream out = new FileOutputStream("slide-" + (i + 1) + ".png");
            javax.imageio.ImageIO.write(img, "png", out);
            out.close();
            //ImageIcon icon = new ImageIcon("slide-" + (i + 1) + ".png");*/
            ImageIcon icon = new ImageIcon(img);
            lblPresentasi.setIcon(icon);
// Obtain metrics about the slide: its number and name
            int number = slides[currentPage-1].getSlideNumber();
            String title = slides[currentPage-1].getTitle();
            // Obtain the embedded text in the slide
            TextRun[] textRuns = slides[currentPage-1].getTextRuns();
            System.out.println("Slide " + number + ": " + title);
            System.out.println("\tText Runs");
            txtArea.setText("Slide : " + number + " Title : " + title + "\n");
            for (int j = 0; j < textRuns.length; j++) {
                // Display each of the text runs present on the slide
                System.out.println("\t\t" + j + ": " + textRuns[j].getText());
                temp=txtArea.getText();
                txtArea.setText(temp+"\t\t" + textRuns[j].getText() + "\n");
            }

            // Obtain the notes for this slide
            System.out.println("\tNotes: ");
            Notes notes = slides[currentPage-1].getNotesSheet();
            if (notes != null) {
                // Notes are comprised of an array of text runs
                TextRun[] notesTextRuns = notes.getTextRuns();
                for (int j = 0; j < notesTextRuns.length; j++) {
                    System.out.println("\t\t" + notesTextRuns[j].getText());
                }
            }


    } catch (Exception e) {
        e.printStackTrace();
    }
    }

Can anyone please help, I am trying to make a simple powerpoint editor in Java. I want to change text in textarea press save button so text has to change and call display function.