How to use

ObservableObjectValue

in

javafx.beans.value

  @Override
  protected T computeValue() { return source.get(); }
};

this.stateProperty().addListener((observable, oldValue, newValue) -> updateSelectAllCheckbox(checkBox));
updateSelectAllCheckbox(checkBox);

public double getViewportLength() {
  return orientation.length(viewportBounds.get());
}

public double getViewportBreadth() {
  return orientation.breadth(viewportBounds.get());
}

private void updateSelectAllCheckbox(@Nonnull CheckBox selectAllCheckBox) {
 switch (stateProperty().get()) {
  case UNSELECTED:
   selectAllCheckBox.setIndeterminate(false);
   selectAllCheckBox.setSelected(false);
   return;
  case INDETERMINATE:
   selectAllCheckBox.setIndeterminate(true);
   return;
  case SELECTED:
   selectAllCheckBox.setIndeterminate(false);
   selectAllCheckBox.setSelected(true);
   return;
 }
 throw new IllegalArgumentException("Invalid state <" + stateProperty().get() + ">");
}