JTabbedPane: Scrollable Tabs

Previously with JTabbedPane, if all the tabs did not fit within a single tab run, the JTabbedPane wrapped tabs onto multiple runs. There have been many requests to provide an alternative scheme, where the JTabbedPane would instead display a single, scrollable run of tabs. This document describes the new API for providing such scrollable tab support in JTabbedPane for the 1.4 release. The bugtraq report that corresponds to this change is: 4093898.

The Too-Many-Tabs Dilemma

Wrapping tabs onto multiple lines provides the benefit of always allowing the user to view all possible tab selections at a given time:

Graphic with two rows of tabs. The first row has five, the second row has four.

However, the problem with multiple runs is in handling the case where the user selects a tab in a run which is not adjacent to the panel display area. For the Windows and Motif look and feel implementations, this action will cause the runs to rotate such that the run containing the selected tab is placed adjacent to the panel display area.

Graphic with selected tab adjacent to panel display area

This behavior can be extremely disorienting to the user because it constantly re-arranges the tabs, eliminating predictability in the UI. The Metal look and feel solved this problem by always leaving the runs fixed, even if the selected tab is not adjacent to the panel display area:

Graphic with selected tab is denoted by different color

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 constraining 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:

Graphic with a single row of tabs that does not include all the possible choices

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 now supports it as an option.

New JTabbedPane API

To allow programs to define which tab layout behavior they require, we now provide a "tabLayoutPolicy" bound property on JTabbedPane:

    public void setTabLayoutPolicy(int layoutPolicy)

    public boolean getTabLayoutPolicy()

Additionally, constants for the supported policy values have been added to JTabbedPane:

    public static final int WRAP_TAB_LAYOUT = 0;

    public static final int SCROLL_TAB_LAYOUT = 1;

Compatibility

This feature had no impact on compatibility, as the default value for the tabLayoutPolicy property is WRAP_TAB_LAYOUT which matches the previous layout behavior of the tabbed pane.

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