PaginationSample Javafx无法为最终变量分页赋值

Question

我试图从oracle样本中复制一个分页样本，但当我导入项目时，发生了一些奇怪的事情，导致我无法构建和运行该项目：

完整的代码是：

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Node;
import javafx.scene.control.*;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.VBox;
import javafx.util.Callback;

public class PaginationSample extends Application {

    private final Pagination pagination;
    private Image[] images = new Image[7];

    private void init(Stage primaryStage) {
        Group root = new Group();
        primaryStage.setScene(new Scene(root));
        VBox outerBox = new VBox();
        outerBox.setAlignment(Pos.CENTER);

        //Images for our pages
        for (int i = 0; i < 7; i++) {
            images[i] = new Image(PaginationSample.class.getResource("animal" + (i + 1) + ".jpg").toExternalForm(), false);
        }

        pagination = PaginationBuilder.create().pageCount(7).pageFactory(new Callback<Integer, Node>() {
            @Override public Node call(Integer pageIndex) {
                return createAnimalPage(pageIndex);
            }
        }).build();
        //Style can be numeric page indicators or bullet indicators
        Button styleButton = ButtonBuilder.create().text("Toggle pagination style").onAction(new EventHandler<ActionEvent>() {
            public void handle(ActionEvent me) {
                if (!pagination.getStyleClass().contains(Pagination.STYLE_CLASS_BULLET)) {
                    pagination.getStyleClass().add(Pagination.STYLE_CLASS_BULLET);
                } else {
                    pagination.getStyleClass().remove(Pagination.STYLE_CLASS_BULLET);
                }
            }
        }).build();

        outerBox.getChildren().addAll(pagination, styleButton);
        root.getChildren().add(outerBox);
    }
    //Creates the page content
    private VBox createAnimalPage(int pageIndex) {
        VBox box = new VBox();
        ImageView iv = new ImageView(images[pageIndex]);
        box.setAlignment(Pos.CENTER);
        Label desc = new Label("PAGE " + (pageIndex + 1));
        box.getChildren().addAll(iv, desc);
        return box;
    }

    @Override public void start(Stage primaryStage) throws Exception {
        init(primaryStage);
        primaryStage.show();
    }
    public static void main(String[] args) { launch(args); }
}

但netbeans向我显示了以下行的错误"cannot assign a value to final variable value“：

pagination = PaginationBuilder.create().pageCount(7).pageFactory(new Callback<Integer, Node>() {

谁能给我解释一下出了什么问题？？

Answer 1

最后一个字段只能初始化一次。因此，初始化它的最佳位置是在声明

private final Pagination pagination = new Pagination(...);

也可以在构造函数中完成，因为构造函数保证每个实例调用一次

private final Pagination pagination;

public PaginationSample() {
    pagination = new Pagination(...);
}

final字段不能在方法中进行初始化，因为一旦创建了该类的实例，就可以多次调用该方法