Horizontally fill tabs of a JTabbedPane

• download example.jar
• download src.zip
• repository

Code

//horizontal filling, same width tabs
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++) {
      JLabel l = (JLabel)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);
  }
}

References

• Horizontally fill tabs of a JTabbedPane(Japanese)