FileChooser fc = FileChooserBuilder.create().extensionFilters(new FileChooser.ExtensionFilter("My File Type", "myext"))
.title("Save My File")
.initialDirectory(initDir)
.build();
fc.showSaveDialog(someNode.getScene().getWindow());

Shows a save dialog with an "Open" button. FileChooserBuilder does not have any method to override the button text (it should).