如何从组合框中获取选定的字符串？

Question

This is my main class. I'm trying to get the string that is being selected from the combobox and "get the wall color" from that string. The problem is that when I run the application, after hitting the playbutton I get an error saying that in line 75 - if (stringWallColor.equals("Default - Black")) , stringWallColor is null.

Does that I mean that it uses the public static String stringWallColor which is null as default? And how can I fix this?

public static String stringWallColor;

    public static void main(String[] args) {
        launch(args);
        System.out.println("Done!");
    }

    public void start(Stage primaryStage) throws Exception {

        Main.primaryStage = primaryStage;

        MenuBar MENU = new MenuBar();
        MenuGenerator.menuCreator(MENU);
        Button playButton = new Button("Play Game");

        ComboBox<String> wallColorCombo = new ComboBox<>();
        wallColorCombo.setPromptText("Choose wall color");
        wallColorCombo.getItems().addAll(
                "Default - Black",
                "Dark Green",
                "Dark Red",
                "Dark Gray",
                "Saddle Brown",
                "Midnight Blue",
                "Dark Magenta",
                "Crimson",
                "Navy");
        stringWallColor = wallColorCombo.getSelectionModel().getSelectedItem();

        gameGrid = new GridPane();
        GridPane root = new GridPane();
        root.add(MENU,0,0);
        root.add(gameGrid, 0, 1);
        gameScene = new Scene(root,600,625);

        GridPane startGrid = new GridPane();
        startGrid.setHgap(20);
        startGrid.setVgap(20);
        playButton.setLineSpacing(10);
        startGrid.add(playButton,8,12);
        startGrid.add(wallColorCombo,7,12);
        GridPane root0= new GridPane();
        root0.add(startGrid,0,1);
        Scene startScene = new Scene(root0, 400, 400);

        primaryStage.setScene(startScene);
        primaryStage.setTitle(GameEngine.GAME_NAME);
        primaryStage.show();
        System.out.println("Default save file not loaded yet");

        playButton.setOnAction(e -> {
            MenuGenerator.loadDefaultSaveFile(primaryStage);
            System.out.println("Default save file loaded");
            primaryStage.setScene(gameScene); });
    }

    public static Color getWallColor() {
        Color wallColor = Color.BLACK;

        if (stringWallColor.equals("Default - Black"))
            wallColor = Color.BLACK;
        if (stringWallColor.equals("Dark Green"))
            wallColor = Color.DARKGREEN;
        if (stringWallColor.equals("Dark Red"))
            wallColor = Color.DARKRED;
        if (stringWallColor.equals("Dark Gray"))
            wallColor = Color.DARKGRAY;
        if (stringWallColor.equals("Saddle Brown"))
            wallColor = Color.SADDLEBROWN;
        if (stringWallColor.equals("Midnight Blue"))
            wallColor = Color.MIDNIGHTBLUE;
        if (stringWallColor.equals("Dark Magenta"))
            wallColor = Color.DARKMAGENTA;
        if (stringWallColor.equals("Crimson"))
            wallColor = Color.CRIMSON;
        if (stringWallColor.equals("Navy"))
            wallColor = Color.NAVY;

        return wallColor;
    }
}

Answer 1

Solved by setting stringWallColor = wallColorCombo.getSelectionModel().getSelectedItem(); as an action for the playbutton.