Image Scroller-scrollbar-LINE_UP,LINE_DOWN-PAGE-UP-PAGE-DOWN

import java.awt.*;
import java.applet.*;
import java.net.URL;

class PanelWithScrollable extends Canvas {
    Image imgObj;
    int paddingX = 0;
    int paddingY = 0;
    Dimension dimObj;

    PanelWithScrollable(Image img, Dimension prefSize) {
        imgObj = img;
        dimObj = prefSize;
    }

    public Dimension minimumSize() {
        return new Dimension(10, 10);
    }

    public Dimension dimObj() {
        return dimObj;
    }

    public void paint(Graphics g) {
        g.translate(-paddingX, -paddingY);
        g.drawImage(imgObj, 0, 0, getBackground(), this);
    }
}

public class ImageScroller extends Applet {
    Scrollbar verticalScroll;
    Scrollbar horziontalScroll;
    PanelWithScrollable canvas;
    boolean startApplet = true;
    String imgObjFile = "../src/image.gif";
    Dimension imgObjSize = new Dimension(720, 420);
    Dimension preferredImageSize = new Dimension(400, 200);

    //This method assumes this Applet is visible.
    public void init() {
        Image img;

        if (startApplet) {
            img = getImage(getCodeBase(), imgObjFile);
        } else {
            img = Toolkit.getDefaultToolkit().getImage(imgObjFile);
        }
        canvas = new PanelWithScrollable(img, preferredImageSize);

        //Create horizontal scrollbar.
        horziontalScroll = new Scrollbar(Scrollbar.HORIZONTAL);

        //Create vertical scrollbar.
        verticalScroll = new Scrollbar(Scrollbar.VERTICAL);

        //Add Components to the Applet.
        setLayout(new BorderLayout());
        add("Center", canvas);
        add("East", verticalScroll);
        add("South", horziontalScroll);

        validate();

        //Now that we've validated, then assuming this Applet is
        //visible, the canvas size is valid and we can adjust the
        //scrollbars to match the image area. [CHECK]
        changeSizeX();
        changeSizeY();
    }

    public boolean handleEvent(Event evt) {
        switch (evt.id) {
          case Event.SCROLL_LINE_UP:
          case Event.SCROLL_LINE_DOWN:
          case Event.SCROLL_PAGE_UP:
          case Event.SCROLL_PAGE_DOWN:
          case Event.SCROLL_ABSOLUTE:
            if (evt.target == verticalScroll) {
                canvas.paddingY = ((Integer)evt.arg).intValue();
                canvas.repaint();
            }
            if (evt.target == horziontalScroll) {
                canvas.paddingX = ((Integer)evt.arg).intValue();
                canvas.repaint();
            }
        }
        return super.handleEvent(evt);
    }

    //Don't call this until the canvas size is valid.
    void changeSizeX() {
        int canvasWidth = canvas.size().width;

        if (canvasWidth <= 0) {
            System.out.println("Canvas has no width; can't resize scrollbar");
            return;
        }

        //Shift everything to the right if we're displaying empty space
        //on the right side.
        if ((canvas.paddingX + canvasWidth) > imgObjSize.width) {
            int newpaddingX = imgObjSize.width - canvasWidth;
            if (newpaddingX < 0) {
                newpaddingX = 0;
            }
            canvas.paddingX = newpaddingX;
        }

        horziontalScroll.setValues(//draw the part of the image that starts at this x:
                       canvas.paddingX, 
                       //amount to scroll for a "page":
                       (int)(canvasWidth * 0.9), 
                       //minimum image x to specify:
                       0,
                       //maximum image x to specify:
                       imgObjSize.width - canvasWidth);
        //"visible" arg to setValues() has no effect after scrollbar is visible.
        horziontalScroll.setPageIncrement((int)(canvasWidth * 0.9));
        return;
    }

    //Don't call this until the canvas size is valid.
    void changeSizeY() {
        int canvasHeight = canvas.size().height;

        if (canvasHeight <= 0) {
            System.out.println("Canvas has no height; can't resize scrollbar");
            return;
        }

        //Shift everything downward if we're displaying empty space
        //on the bottom.
        if ((canvas.paddingY + canvasHeight) > imgObjSize.height) {
            int newpaddingY = imgObjSize.height - canvasHeight;
            if (newpaddingY < 0) {
                newpaddingY = 0;
            }
            canvas.paddingY = newpaddingY;
        }

        verticalScroll.setValues(//initially draw part of image starting at this y:
                       canvas.paddingY, 
                       //visible arg--amount to scroll for a "page":
                       (int)(canvasHeight * 0.9), 
                       //minimum image y to specify:
                       0,
                       //maximum image y to specify:
                       imgObjSize.height - canvasHeight);

        //"visible" arg to setValues() has no effect after scrollbar is visible.
        verticalScroll.setPageIncrement((int)(canvasHeight * 0.9));
        return;
    }

    public void paint(Graphics g) {
        //This method probably was called due to applet being resized.
        changeSizeX();
        changeSizeY();

        return;
    }
}