JFrameの縦横比を一定にする

private static final int MW = 320;
private static final int MH = 200;
// ...
frame.addComponentListener(new ComponentAdapter() {
  @Override public void componentResized(ComponentEvent e) {
    int fw = frame.getSize().width;
    int fh = MH * fw / MW;
    frame.setSize(MW > fw ? MW : fw, MH > fh ? MH : fh);
  }
});