Why is my compareTo method giving errors?

Question

I'm using Eclipse and it's giving me an error saying "Cannot invoke compareTo(int) on the primitive type int". Here is my code:

    namespace Laser_Control2
    {
    public partial class LaserControlForm : Form
    {
        public LaserControlForm()
        {
            InitializeComponent();
        }

        // Manipulate a bitmap image
        // Extract the pixel map data
        // To run this example, paste it into a form and handle the form's Paint event
        //  by calling the LockUnlockBitsExample method, passing e as PaintEventArgs.
        private void LockUnlockBitsExample(PaintEventArgs e)
        {

            // Create a new bitmap.
            Bitmap bmp = new Bitmap("c:\\fakePhoto.jpg");

            // Lock the bitmap's bits.  
            Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
            System.Drawing.Imaging.BitmapData bmpData =
                bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,
                bmp.PixelFormat);

            // Get the address of the first line.
            IntPtr ptr = bmpData.Scan0;

            // Declare an array to hold the bytes of the bitmap.
            int bytes = Math.Abs(bmpData.Stride) * bmp.Height;
            byte[] rgbValues = new byte[bytes];

            // Copy the RGB values into the array.
            System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes);

            // Set every third value to 255. A 24bpp bitmap will look red.  
            for (int counter = 2; counter < rgbValues.Length; counter += 3)
                rgbValues[counter] = 255;

            // Copy the RGB values back to the bitmap
            System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes);

            // Unlock the bits.
            bmp.UnlockBits(bmpData);

            // Draw the modified image.
            e.Graphics.DrawImage(bmp, 0, 150);

        }
        private void loadPdfButton_Click(object sender, EventArgs e)
        {
            if(openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                PdfDocument doc = new PdfDocument();                                                // Create Spire object - a new document
                doc.LoadFromFile(@"E:/Test/test2.pdf");                                             // Load test2.pdf into new document
                Image bmp = doc.SaveAsImage(0, 0, 32, 32);                                          // Save the .pdf doc as a .bmp

                pictureBox1.Image = bmp;
                bmp.Save("convertToBmp.bmp", System.Drawing.Imaging.ImageFormat.Bmp);
                System.Diagnostics.Process.Start("convertToBmp.bmp");

            }
        }

        private void clearButton_Click(object sender, EventArgs e)
        {
            this.Close();
        }

    }
}

---

The example we were given in class does a similar thing except it is using a double value, so I'm not sure why the file from class works, but mine doesn't. I'd appreciate any help.

Example from class:

public class ReadingMaterial implements Comparable<ReadingMaterial> {

    private int pages;
    private String title;
    private String author;


    public ReadingMaterial(int pages, String title, String author) 
    {
        super();
        this.title = title;
        this.pages = pages;
        this.author = author;

    }

    public int getPages() 
    {
        return pages;
    }

    public void setPages(int pages) 
    {
        this.pages = pages;
    }


    public String getAuthor() 
    {
        return author;
    }

    public void setAuthor(String author) 
    {
        this.author = author;
    }

    public String getTitle() 
    {
        return title;
    }

    public void setTitle(String title) 
    {
        this.title = title;
    }

    @Override
    public int compareTo(ReadingMaterial o) {

        if(pages.compareTo(o.getPages()) > 0)
            return -1;
        else if(pages.compareTo(o.getPages()) < 0)
            return 1;
        else
        {
            return 0;
        }
    }

    @Override
    public String toString() 
    {
        return "The reading material you selected is titled " + title + " with" + pages + "pages. It is written by " + author + ".";

    }

}