Swing/ClippedTabLabel のバックアップ(No.18)

class ClippedTitleTabbedPane extends JTabbedPane {
  public ClippedTitleTabbedPane() {
    super();
  }
  public ClippedTitleTabbedPane(int tabPlacement) {
    super(tabPlacement);
  }
  private Insets getTabInsets() {
    Insets i = UIManager.getInsets("TabbedPane.tabInsets");
    if (i != null) {
      return i;
    } else {
      SynthStyle style = SynthLookAndFeel.getStyle(this, Region.TABBED_PANE_TAB);
      SynthContext context = new SynthContext(
        this, Region.TABBED_PANE_TAB, style, SynthConstants.ENABLED);
      return style.getInsets(context, null);
    }
  }
  private Insets getTabAreaInsets() {
    Insets i = UIManager.getInsets("TabbedPane.tabAreaInsets");
    if (i != null) {
      return i;
    } else {
      SynthStyle style = SynthLookAndFeel.getStyle(this, Region.TABBED_PANE_TAB_AREA);
      SynthContext context = new SynthContext(
        this, Region.TABBED_PANE_TAB_AREA, style, SynthConstants.ENABLED);
      return style.getInsets(context, null);
    }
  }
  @Override public void doLayout() {
    int tabCount  = getTabCount();
    if (tabCount == 0) return;
    Insets tabInsets   = getTabInsets();
    Insets tabAreaInsets = getTabAreaInsets();
    Insets insets = getInsets();
    int areaWidth = getWidth() - tabAreaInsets.left - tabAreaInsets.right
                    - insets.left        - insets.right;
    int tabWidth  = 0; // = tabInsets.left + tabInsets.right + 3;
    int gap     = 0;

    switch (getTabPlacement()) {
    case LEFT:
    case RIGHT:
      tabWidth = areaWidth / 4;
      gap = 0;
      break;
    case BOTTOM:
    case TOP:
    default:
      tabWidth = areaWidth / tabCount;
      gap = areaWidth - (tabWidth * tabCount);
    }
    // "3" is magic number @see BasicTabbedPaneUI#calculateTabWidth
    tabWidth = tabWidth - tabInsets.left - tabInsets.right - 3;
    for (int i = 0; i < tabCount; i++) {
      JComponent l = (JComponent)getTabComponentAt(i);
      if (l == null) break;
      l.setPreferredSize(new Dimension(tabWidth + (i < gap ? 1 : 0), l.getPreferredSize().height));
    }
    super.doLayout();
  }
  @Override public void insertTab(
      String title, Icon icon, Component component, String tip, int index) {
    super.insertTab(title, icon, component, tip == null ? title : tip, index);
    JLabel label = new JLabel(title, JLabel.CENTER);
    Dimension dim = label.getPreferredSize();
    Insets tabInsets = getTabInsets();
    label.setPreferredSize(new Dimension(0, dim.height + tabInsets.top + tabInsets.bottom));
    setTabComponentAt(index, label);
  }
}