https://forums.oracle.com/forums/message.jspa?messageID=10219772

If you set the text in the constructor, the center of the text is in the center of the control.
But if you set the text programmatically (and the text was previously empty), then then the left side of the text is in the center of the control.

final TextField tf = new TextField();
Button btn = new Button("update");
btn.setOnAction(new EventHandler<ActionEvent>(){

@Override
public void handle(ActionEvent t) {
tf.setText("Hello");
}
});
tf.setAlignment(Pos.CENTER);
tf.setMinSize(200, 24);
tf.setMaxSize(200, 40);
tf.setPrefSize(200, 40);
tf.setStyle("-fx-font: 20 arial;");