package application;

import javafx.application.*;
import javafx.stage.*;
import javafx.scene.*;
import javafx.scene.layout.*;
import javafx.fxml.*;


public class App extends Application {
	@Override
	public void start(Stage primaryStage) {
		try {
			GridPane root = (GridPane)FXMLLoader.load(getClass().getResource("App.fxml"));
			Scene scene = new Scene(root, 540, 400);
			primaryStage.setScene(scene);
			primaryStage.show();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		launch(args);
	}
}

package application;

import javafx.application.*;
import javafx.stage.*;
import javafx.scene.*;
import javafx.scene.layout.*;
import javafx.fxml.*;


public class App extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
            GridPane root = (GridPane)FXMLLoader.load(getClass().getResource("App.fxml"));
            Scene scene = new Scene(root, 540, 400);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Change indentation of App.java