JTabbedPane: Scrollable Tabs

• The Too-Many-Tabs Dilemma
• New JTabbedPane API
• Compatibility

The Too-Many-Tabs Dilemma

Unfortunately the downside of the Metal solution is that it visually departs from the 'tabbed folder' metaphor (the selected tab is not 'attached' to its content). In fact, Chapter 7 of the Java Look and Feel Guidelines recommends against creating tabbed panes with multiple runs:

"If your tabbed pane requires multiple rows of tabs, consider dividing the content among several dialog boxes or components. Multiple rows of tabs can be confusing."

While contraining tabs in a tabbed pane to a number which will fit within a single run is an important UI guideline, there are circumstances where a proliferation of tabs cannot be avoided. This is often the case if the tabs are created dynamically by the application at runtime (perhaps driven off the content of a database).

An alternate solution for handling the tab proliferation case is to constrain the tabbed pane to a single, scrollable run of tabs:

Naturally, this solution has its own set of usability problems, the most obvious of which is that the user can no longer view all possible selections at one time. However, this scrollable-tab behavior is becoming increasingly common in user interfaces and therefore Swing should support it as an option.

New JTabbedPane API

    /**
     * Sets the policy which the tabbedpane will use in laying out the tabs
     * when all the tabs will not fit within a single run.       
     * Possible values are:
     * o JTabbedPane.WRAP_TAB_LAYOUT
     * o JTabbedPane.SCROLL_TAB_LAYOUT
     * 
     * The default value, if not set, is JTabbedPane.WRAP_TAB_LAYOUT.
     *
     * @param layoutPolicy the policy used to layout the tabs
     * @exception IllegalArgumentException if layoutPolicy value isn't one
     *				of the above valid values
     * @see #getTabLayoutPolicy
     * @since 1.4
     *
     * @beaninfo
     *    preferred: true
     *        bound: true
     *    attribute: visualUpdate true
     *         enum: WRAP_TAB_LAYOUT JTabbedPane.WRAP_TAB_LAYOUT
     *               SCROLL_TAB_LAYOUT JTabbedPane.SCROLL_TAB_LAYOUT
     *  description: The tabbedpane's policy for laying out the tabs
     *
     */
    public void setTabLayoutPolicy(int layoutPolicy)

    /**
     * Returns the policy used to layout tabs for this tabbedpane.
     * @see #setTabLayoutPolicy
     * @since 1.4
     */
    public boolean getTabLayoutPolicy()

Additionally, constants for the supported policy values will be added to JTabbedPane:

   /**
    * The tab layout policy for wrapping tabs in multiple runs when all
    * tabs will not fit within a single run.
    */
    public static final int WRAP_TAB_LAYOUT = 0;

   /**
    * The tab layout policy for providing a scrollable region of tabs
    * when all the tabs will not fit within a single run.  A pair of
    * scroll buttons are provided for the user to control the scrolling.
    * The placement of the scroll buttons is determined by the look&feel.
    */
    public static final int SCROLL_TAB_LAYOUT = 1;

Compatibility