JTabbedPane風のタブ配置をレイアウトマネージャーで変更

class TabLayout implements LayoutManager, Serializable {
  private static final long serialVersionUID = 1L;
  private static final int TAB_WIDTH = 100;
  @Override public void addLayoutComponent(String name, Component comp) {
    /* not needed */
  }

  @Override public void removeLayoutComponent(Component comp) {
    /* not needed */
  }

  @Override public Dimension preferredLayoutSize(Container parent) {
    synchronized (parent.getTreeLock()) {
      Insets insets = parent.getInsets();
      int last = parent.getComponentCount() - 1;
      int w = 0;
      int h = 0;
      if (last >= 0) {
        Component comp = parent.getComponent(last);
        Dimension d = comp.getPreferredSize();
        w = d.width;
        h = d.height;
      }
      return new Dimension(insets.left + insets.right + w,
                           insets.top + insets.bottom + h);
    }
  }

  @Override public Dimension minimumLayoutSize(Container parent) {
    synchronized (parent.getTreeLock()) {
      return new Dimension(100, 24);
    }
  }

  @Override public void layoutContainer(Container parent) {
    synchronized (parent.getTreeLock()) {
      int ncomponents = parent.getComponentCount();
      if (ncomponents == 0) {
        return;
      }
      // int nrows = 1;
      // boolean ltr = parent.getComponentOrientation().isLeftToRight();
      Insets insets = parent.getInsets();
      int ncols = ncomponents - 1;
      int lastw = parent.getComponent(ncomponents - 1).getPreferredSize().width;
      int width = parent.getWidth() - insets.left - insets.right - lastw;
      int h = parent.getHeight() - insets.top - insets.bottom;
      int w = width > TAB_WIDTH * ncols ? TAB_WIDTH : width / ncols;
      int gap = width - w * ncols;
      int x = insets.left;
      int y = insets.top;
      for (int i = 0; i < ncomponents; i++) {
        int cw = i == ncols ? lastw : w + (gap-- > 0 ? 1 : 0);
        parent.getComponent(i).setBounds(x, y, cw, h);
        x += cw;
      }
    }
  }

  @Override public String toString() {
    return getClass().getName();
  }
}