JTabbedPaneで直前に選択されていたタブのフォーカスBorderを履歴として表示する

class LineFocusTabbedPane extends JTabbedPane {
  private transient ChangeListener listener;

  protected LineFocusTabbedPane() {
    super();
  }

  @Override public void updateUI() {
    removeChangeListener(listener);
    UIManager.put("TabbedPane.tabInsets", new InsetsUIResource(1, 4, 0, 4));
    UIManager.put("TabbedPane.selectedTabPadInsets", new InsetsUIResource(1, 1, 1, 1));
    UIManager.put("TabbedPane.tabAreaInsets", new InsetsUIResource(3, 2, 0, 2));
    UIManager.put("TabbedPane.selectedLabelShift", 0);
    UIManager.put("TabbedPane.labelShift", 0);
    UIManager.put("TabbedPane.focus", new ColorUIResource(new Color(0x0, true)));
    super.updateUI();
    listener = new TabSelectionListener();
    addChangeListener(listener);
    setTabLayoutPolicy(JTabbedPane.SCROLL_TAB_LAYOUT);
  }

  @Override public void insertTab(String title, Icon icon, Component c, String tip, int index) {
    super.insertTab(title, icon, c, tip, index);
    JLabel label = new JLabel(title, icon, SwingConstants.CENTER);
    setTabComponentAt(index, label);
  }
}

class TabSelectionListener implements ChangeListener {
  private static final Color ALPHA_ZERO = new Color(0x0, true);
  private static final Color SELECTION_COLOR = new Color(0x00_AA_FF);
  private static final Color PREV_COLOR = new Color(0x48_00_AA_FF, true);
  private int prev = -1;

  @Override public void stateChanged(ChangeEvent e) {
    JTabbedPane tabbedPane = (JTabbedPane) e.getSource();
    if (tabbedPane.getTabCount() <= 0) {
      return;
    }
    int idx = tabbedPane.getSelectedIndex();
    for (int i = 0; i < tabbedPane.getTabCount(); i++) {
      Component tab = tabbedPane.getTabComponentAt(i);
      if (tab instanceof JComponent) {
        Color color;
        if (i == idx) {
          color = SELECTION_COLOR;
        } else if (i == prev) {
          color = PREV_COLOR;
        } else {
          color = ALPHA_ZERO;
        }
        ((JComponent) tab).setBorder(BorderFactory.createMatteBorder(3, 0, 0, 0, color));
      }
    }
    prev = idx;
  }
}