LayoutManagerを使ってパネルの展開アニメーションを行う

private Timer animator;
private boolean isHidden = true;
private final JPanel controls = new JPanel(new BorderLayout(5, 5) {
  private int controlsHeight;
  private int controlsPreferredHeight;
  @Override public Dimension preferredLayoutSize(Container target) {
    // synchronized (target.getTreeLock()) {
    Dimension ps = super.preferredLayoutSize(target);
    controlsPreferredHeight = ps.height;
    if (animator != null) {
      if (isHidden) {
        if (controls.getHeight() < controlsPreferredHeight) {
          controlsHeight += 5;
        }
      } else {
        if (controls.getHeight() > 0) {
          controlsHeight -= 5;
        }
      }
      if (controlsHeight <= 0) {
        controlsHeight = 0;
        animator.stop();
      } else if (controlsHeight >= controlsPreferredHeight) {
        controlsHeight = controlsPreferredHeight;
        animator.stop();
      }
    }
    ps.height = controlsHeight;
    return ps;
  }
});

private Action makeShowHideAction() {
  return new AbstractAction("Show/Hide Search Box") {
    @Override public void actionPerformed(ActionEvent e) {
      if (animator != null && animator.isRunning()) {
        return;
      }
      isHidden = controls.getHeight() == 0;
      animator = new Timer(5, new ActionListener() {
        @Override public void actionPerformed(ActionEvent e) {
          controls.revalidate();
        }
      });
      animator.start();
    }
  };
}