Swing/DividerSplitRatio のバックアップ(No.10)

class SplitPaneWrapper extends JPanel {
  private int prevState = Frame.NORMAL;
  private final JSplitPane splitPane;

  protected SplitPaneWrapper(JSplitPane splitPane) {
    super(new BorderLayout());
    this.splitPane = splitPane;
    add(splitPane);
    EventQueue.invokeLater(() -> splitPane.setDividerLocation(.5));
  }

  private static int getOrientedSize(JSplitPane sp) {
    return (sp.getOrientation() == JSplitPane.VERTICAL_SPLIT)
           ? sp.getHeight() - sp.getDividerSize()
           : sp.getWidth() - sp.getDividerSize();
  }

  @Override public void doLayout() {
    int size = getOrientedSize(splitPane);
    final double proportionalLocation = splitPane.getDividerLocation() / (double) size;
    super.doLayout();
    int state = ((Frame) SwingUtilities.getWindowAncestor(splitPane)).getExtendedState();
    if (splitPane.isShowing() && state != prevState) {
      EventQueue.invokeLater(() -> {
        int s = getOrientedSize(splitPane);
        int iv = (int) Math.round(s * proportionalLocation);
        System.out.format("DividerLocation: %d%n", iv);
        splitPane.setDividerLocation(iv);
      });
      prevState = state;
    }
  }
}