import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.control.Button;
import javafx.geometry.Pos;

public class HeiPerson extends Application {

    public void start(Stage stage) {
        VBox root = new VBox();
        root.setAlignment(Pos.CENTER);

        Label hilsen = new Label("Hei ...");
        TextField tekstfelt = new TextField("Skriv ditt navn:");

        Button button = new Button("Si hei");
        button.setOnAction(e -> {
            String navn = tekstfelt.getText();
            hilsen.setText("Hei " + navn);
        });

        root.getChildren().addAll(hilsen, tekstfelt, button);

        stage.setScene(new Scene(root));
        stage.show();
    }
}