Question

I have created JTextpane and inserted components inside textpane (components like Jtextarea). (vertical scrollbar of )Jscrollpane of JTextpane is automatically set to bottom when I insert new components in that JTextpane. I want to keep it to be set to the top position. How can I do this

Thanks
Sunil Kumar Sahoo

Answer 1

Here’s a utility class I use. It can be used to scroll to the top, bottom, left, right or horizonatal / vertical center of a JScrollPane.

public final class ScrollUtil {
    public static final int NONE = 0, TOP = 1, VCENTER = 2, BOTTOM = 4, LEFT = 8, HCENTER = 16, RIGHT = 32;
    private static final int OFFSET = 100; // Required for hack (see below).

    private ScrollUtil() {
    }

    /**
     * Scroll to specified location.  e.g. <tt>scroll(component, BOTTOM);</tt>.
     *
     * @param c JComponent to scroll.
     * @param part Location to scroll to.  Should be a bit-wise OR of one or moe of the values:
     * NONE, TOP, VCENTER, BOTTOM, LEFT, HCENTER, RIGHT.
     */
    public static void scroll(JComponent c, int part) {
        scroll(c, part & (LEFT|HCENTER|RIGHT), part & (TOP|VCENTER|BOTTOM));
    }

    /**
     * Scroll to specified location.  e.g. <tt>scroll(component, LEFT, BOTTOM);</tt>.
     *
     * @param c JComponent to scroll.
     * @param horizontal Horizontal location.  Should take the value: LEFT, HCENTER or RIGHT.
     * @param vertical Vertical location.  Should take the value: TOP, VCENTER or BOTTOM.
     */
    public static void scroll(JComponent c, int horizontal, int vertical) {
        Rectangle visible = c.getVisibleRect();
        Rectangle bounds = c.getBounds();

        switch (vertical) {
            case TOP:     visible.y = 0; break;
            case VCENTER: visible.y = (bounds.height - visible.height) / 2; break;
            case BOTTOM:  visible.y = bounds.height - visible.height + OFFSET; break;
        }

        switch (horizontal) {
            case LEFT:    visible.x = 0; break;
            case HCENTER: visible.x = (bounds.width - visible.width) / 2; break;
            case RIGHT:   visible.x = bounds.width - visible.width + OFFSET; break;
        }

        // When scrolling to bottom or right of viewport, add an OFFSET value.
        // This is because without this certain components (e.g. JTable) would
        // not scroll right to the bottom (presumably the bounds calculation
        // doesn't take the table header into account.  It doesn't matter if
        // OFFSET is a huge value (e.g. 10000) - the scrollRectToVisible method
        // still works correctly.

        c.scrollRectToVisible(visible);
    }
}