java - SwingWorker - 相同的变量在 sysout 和 GUI 上显示不同的值

Question

编辑:请注意，这个问题与我的其他问题相关:SwingWorker - Passing parameters and returning an ArrayList<Object>

在深入研究 SwingWorker 后，为了尝试解决这个问题，我想出了这个 SSCCE 代码。

注释结束

编辑结束

给出以下 SSCCE 代码:

import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

public class MainFrame extends JFrame {

    private JLabel countLabel1 = new JLabel("0");
    private JLabel statusLabel1 = new JLabel("Task not completed.");
    private JLabel statusLabel2 = new JLabel("Task not completed.");
    private JLabel statusLabel3 = new JLabel("Task not completed.");
    private JButton startButton = new JButton("Start");
    private ArrayList<Train> trainList = new ArrayList<>();
    private ArrayList<Train> processedTrains = new ArrayList<>();

    public MainFrame(String title) {
        super(title);

        setLayout(new GridBagLayout());

        countLabel1.setFont(new Font("serif", Font.BOLD, 28));

        GridBagConstraints gc = new GridBagConstraints();

        gc.fill = GridBagConstraints.NONE;

        gc.gridx = 0;
        gc.gridy = 0;
        gc.weightx = 1;
        gc.weighty = 1;
        add(countLabel1, gc);

        gc.gridx = 0;
        gc.gridy = 1;
        gc.weightx = 1;
        gc.weighty = 1;
        add(statusLabel1, gc);

        gc.gridx = 0;
        gc.gridy = 2;
        gc.weightx = 1;
        gc.weighty = 1;
        add(statusLabel2, gc);

        gc.gridx = 0;
        gc.gridy = 3;
        gc.weightx = 1;
        gc.weighty = 1;
        add(statusLabel3, gc);

        gc.gridx = 0;
        gc.gridy = 4;
        gc.weightx = 1;
        gc.weighty = 1;
        add(startButton, gc);

        Train t1 = new Train();
        t1.setId(1);
        t1.setName("John");

        Train t2 = new Train();
        t2.setId(2);
        t2.setName("Mark");

        Train t3 = new Train();
        t3.setId(3);
        t3.setName("Lewis");


        trainList.add(t1);
        trainList.add(t2);
        trainList.add(t3);


        startButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                TrainMethods tm = new TrainMethods();

                // How can the swing worker return the array from the
                // processTrains method to this processedTrains array
                processedTrains = tm.processTrains(trainList);

                for (int i = 0; i < processedTrains.size(); i++) {
                    System.out.println("Train id: " + processedTrains.get(i).getId()
                            + " Train Name: " + processedTrains.get(i).getName());
                }
            }
        });

        setSize(200, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
    }

    public static void main(String[] args) {
// Notice that it kicks it off on the event-dispatching thread, not the main thread.
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                MainFrame mf = new MainFrame("Yo");
            }
        });
    }

    private class Train {
        String name;
        int id;

        public void setName(String name) {
            this.name = name;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public int getId() {
            return id;
        }
    }

    private class TrainMethods {

        public ArrayList processTrains(final ArrayList<Train> trainList) {
            // Add here a SwingWorker to create a new thread
            // and execute the following code and update later on
            // a progress bar
            SwingWorker<ArrayList, Integer> worker = new SwingWorker<ArrayList, Integer>() {
                @Override
                protected ArrayList doInBackground() throws Exception {
                    for(int i = 0; i<trainList.size(); i++)
                    {
                        trainList.get(i).setName("No name");
                        publish(i);
                    }
                return trainList;
                }

                @Override
                protected void process(List<Integer> chunks) {
                    int mostRecentValue = chunks.get(chunks.size() - 1);
                    countLabel1.setText(Integer.toString(mostRecentValue));
                }

                @Override
                protected void done() {
                    ArrayList<Train> status;
                    try {
                        // Retrieve the return value of doInBackground.
                        status = get();
                        statusLabel1.setText("Completed Train 1 with name: " + status.get(0).getName());
                        statusLabel2.setText("\nCompleted Train 2 with name: " + status.get(1).getName());
                        statusLabel3.setText("\nCompleted Train 3 with name: " + status.get(2).getName());
                    } catch (InterruptedException | ExecutionException ex) {
                        Logger.getLogger(MainFrame.class.getName()).log(Level.SEVERE, null, ex);
                    }
                }
            };
            worker.execute();

            return trainList;

//            for (int i = 0; i < trainList.size(); i++) {
//                trainList.get(i).setName("No name");
//            }
//            return trainList;
        }
    }
}

为什么System.Out.Println()打印:

Train id: 1 Train Name: John
Train id: 2 Train Name: Mark
Train id: 3 Train Name: Lewis

当用户界面打印:No Name？就我个人而言，我希望在两者上都打印No Name。

问题 1:为什么输出不同？

问题2:如何让它在两个地方(Sysout 和 GUI)都输出 No Name？

_________________________ 编辑 _______________________________

问题3:为什么我第二次按下开始按钮时，两者都会打印No Name？

Answer 1

doInBackground() 毫不奇怪地在后台运行。也就是说，它是在另一个线程中执行的。因此，您不能依赖该代码的执行顺序以及您的打印代码。因此trainsList的内容可以在打印之前、之后或期间修改。如果您确实需要立即获得结果，则需要添加一些同步(通常不需要。这就是在另一个线程中运行任务以避免等待任务完成的全部意义所在)。

最有可能的正确解决方案是根本没有打印代码，并让 SwingWorker 按照预期的方式工作。结果可以在 done() 中以线程安全的方式获得(在 process() 中可以在子任务准备就绪后立即获得您需要的任何内容)。

在第二次运行中，您会得到“无名称”，因为您从未将名称重置为其他任何名称，因此它们是在上一次运行中设置的名称。