JAVA:将值从一个类传递到另一个类

Question

我对 Java 还很陌生，几天来我一直在努力解决一个可能非常简单但我真的无法解决的问题。我有两个公共(public)类，都是外部类的内部类。在第一个中，我获取了一些数据(来自眼动仪设备)。在第二个中，我想将它们画在图像上。我正确地获取了数据并将它们存储在数组列表中，但是当我在第二个方法中使用它们时，我得到一个空的数组列表。代码如下:

  import ...

public class TETSimple {
    //static LoadImageApp image = new LoadImageApp();

    public ArrayList x1;
    public ArrayList y1;

    public static void main(String[] args) {
        final GazeManager gm = GazeManager.getInstance();
        boolean success = gm.activate(ApiVersion.VERSION_1_0, ClientMode.PUSH);

        final GazeListener gazeListener = new GazeListener();
        gm.addGazeListener(gazeListener);

        JFrame f = new JFrame("Immagine");

        LoadImageApp a = new LoadImageApp();
        f.add(a);
        f.pack();
        f.setVisible(true);

        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                gm.removeGazeListener(gazeListener);
                gm.deactivate();
            }
        });
    }


    public static class GazeListener
        implements IGazeListener {

        private ArrayList<Double> x1 = new ArrayList<Double>();
        private ArrayList<Double> y1 = new ArrayList<Double>();

        public ArrayList getX1() {
            return this.x1;

        }

        public ArrayList getY1() {
            return this.y1;
        }

        public void setX1(ArrayList l1) {
            x1 = l1;
        }

        public void setY1(ArrayList l2) {
            x1 = l2;
        }

        @Override
        public void onGazeUpdate(GazeData gazeData) {
            Double xcor = gazeData.smoothedCoordinates.x;
            Double ycor = gazeData.smoothedCoordinates.y;

            x1.add(new Double(xcor));
            y1.add(new Double(ycor));

            //System.out.println(x1.toString()); --> it works and returns all the values detected and added into the array
        }
    }

    public static class LoadImageApp
        extends Component {
        BufferedImage img;

        public Integer x;
        public Integer y;

        public void paint(Graphics g) {
            Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
            Double screenW = screenSize.getWidth();
            Double screenH = screenSize.getHeight() * 0.95;

            int screenWidth = screenW.intValue();
            int screenHeight = screenH.intValue();

            // Dimensioni dell'immagine
            if (img == null) {
                return;
            }
            int imageWidth = img.getWidth(this);
            int imageHeight = img.getHeight(this);
            g.drawImage(img, 0, 0, screenWidth, screenHeight, 0, 0, imageWidth, imageHeight, null);
            GazeListener a = new GazeListener();
            System.out.println(a.getX1().toString()); //--> doesn't work, return an empty array

            if (a.x1 != null && !a.x1.isEmpty() && a.y1 != null && !a.y1.isEmpty()) {
                Double currentx = a.x1.get(a.x1.size() - 1);
                Double currenty = a.y1.get(a.x1.size() - 1);
                System.out.println(currentx);
            } else {
                System.out.println("empty array");
            }
        }

        // costruttore della classe:
        public LoadImageApp() {
            try {
                img = ImageIO.read(new File("C:picture.jpg"));
            } catch (IOException e) {
            }
        }

        public Dimension getPreferredSize() {
            if (img == null) {
                return new Dimension(100, 100);
            } else {
                return new Dimension(img.getWidth(null), img.getHeight(null));
            }
        }
    }

换句话说，我想做的是用GazeListener类的onGazeUpdate()方法检测数据x1和x2，然后能够在方法paint(Graphics g)中使用这些数据LoadImageApp 类。

我还为此目的设置了 set/get 方法，但我仍然犯了一些错误。

我错了什么？

提前非常感谢您!

Answer 1

在您的LoadImageApp.paint方法中，您创建一个新的GazeListener实例。您的新实例对您在 main 中创建的实例一无所知。

解决这个问题的方法是在 main 中创建 final GazeListener GalaxyListener = new GazeListener(); ，然后将其传递给 app 作为构造函数参数:LoadImageApp a= new LoadImageApp(gazeListener);。然后，您将其存储为字段并从 Paint 中引用该字段，而不是在 Paint 中创建新实例

作为附加说明，您将 GazeListener 和 LoadImageApp 称为“内部类”。它们不是内部类，而是static member classes 。如果您希望他们表现得像 inner classes他们不会。内部类使您可以访问父实例的字段。您的类无法获得该访问权限，因为它们具有 static 修饰符。

public static class LoadImageApp
    extends Component {
    private GazeListener gazeListener;
    public LoadImageApp(GazeListener aGazeListener) {
        this.gazeListener = aGazeListener;
    }
    ...
    public void paint(Graphics g) {
        ...
        // don't do the next line
        //GazeListener a = new GazeListener();
        //System.out.println(a.getX1().toString()); //--> doesn't work, return an empty array
        System.out.println(this.gazeListener.getX1().toString()); 
        ...
    }
}