为什么即使我使用了 dialog.dispose()，Java 也不能正确关闭？

Question

我在下面发布了完整的代码，但基本上我有一个类，它有一个对话框，其中包含一个包含 jlist 的滚动窗格。它设置为“DISPOSE_ON_CLOSE”，并且我尝试在获得值后将曾经创建的每个变量设置为 null，但 javaw.exe 将继续无限期运行，除非我强行关闭它。

如果需要更多信息，这里有一个简单的解释。此类旨在创建一个对话框并显示它，等待用户输入并返回所选文本。它已经这样做了。但是由于某种原因，它在完成后继续在后台运行。

这适用于应用程序，因此让 Java 在后台不间断运行并不是一个吸引人的前景。在这一点上，我真的不知道还能尝试什么。下面是我的代码。

package (REMOVED);

import java.awt.BorderLayout;
import java.awt.Dialog.ModalityType;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JComponent;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.ListSelectionModel;
import javax.swing.WindowConstants;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

public class PatientScrollPane implements ListSelectionListener, MouseListener {
    private String currentPatient;
    private JList patientList;
    private JDialog dialog;
    private JFrame frame;
    private JScrollPane scrollPane;
    private static int MAX_VISIBLE_ROW_COUNT = 15;

    public void setDialog(JDialog dialog) {
        this.dialog = dialog;
    }

    public JList getPatientList() {
        return patientList;
    }

    public void setPatientList(JList patientList) {
        this.patientList = patientList;
    }

    public String getCurrentPatient() {
        return currentPatient;
    }

    public void setCurrentPatient(String currentPatient) {
        this.currentPatient = currentPatient;
    }

    public JDialog getDialog() {
        return dialog;
    }

    public JFrame getFrame() {
        return frame;
    }

    public void setFrame(JFrame frame) {
        this.frame = frame;
    }

    public JScrollPane getScrollPane() {
        return scrollPane;
    }

    public void setScrollPane(JScrollPane scrollPane) {
        this.scrollPane = scrollPane;
    }

    public PatientScrollPane() {
        this(null);
    }

    public PatientScrollPane(JComponent locationRelativeToComponent) {
        this(locationRelativeToComponent, new JList(fakePatientList()));
    }

    public PatientScrollPane(JComponent locationRelativeToComponent, JList patientList) {
        this.patientList = patientList;
        patientList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

        frame = new JFrame("Patient List");

        dialog = new JDialog(frame);
        dialog.setLocationRelativeTo(locationRelativeToComponent);

        patientList.addListSelectionListener(this);
        patientList.addMouseListener(this);
        setVisibleRowCount();

        scrollPane = new JScrollPane(patientList);
        dialog.getContentPane().add(scrollPane, BorderLayout.CENTER);

        dialog.pack();
        dialog.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
        dialog.setModalityType(ModalityType.APPLICATION_MODAL);
        dialog.setVisible(true);
    }

    private void setVisibleRowCount() {
        int size = patientList.getModel().getSize();

        if(size <= MAX_VISIBLE_ROW_COUNT) {
            patientList.setVisibleRowCount(size);
        } else {
            patientList.setVisibleRowCount(MAX_VISIBLE_ROW_COUNT);
        }
    }

    public static String[] fakePatientList() {
        String[] patients = new String[20];
        for(int i = 0; i < patients.length; i++) {
            patients[i] = "Patient " + i;
        }

        return patients;
    }

    public static String getPatient() {
        PatientScrollPane patientScrollPane = new PatientScrollPane();
        String patient = patientScrollPane.getCurrentPatient();
        patientScrollPane.setPatientList(null);
        patientScrollPane.setDialog(null);
        patientScrollPane.setCurrentPatient(null);
        patientScrollPane.setFrame(null);
        patientScrollPane.setScrollPane(null);
        patientScrollPane = null;

        return patient;
    }

    public static String getPatient(JComponent locationRelativeToComponent) {
        PatientScrollPane patientScrollPane = new PatientScrollPane(locationRelativeToComponent);

        return patientScrollPane.getCurrentPatient();
    }

    public static String getPatient(JComponent locationRelativeToComponent, JList patientList) {
        PatientScrollPane patientScrollPane = new PatientScrollPane(locationRelativeToComponent, patientList);

        String patient = patientScrollPane.getCurrentPatient();
        return patient;
    }

    @Override
    public void valueChanged(ListSelectionEvent e) {
        currentPatient = (String)patientList.getSelectedValue();
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        int index = patientList.locationToIndex(e.getPoint());
        patientList.setSelectedIndex(index);
        dialog.dispose();
    }

    @Override
    public void mouseEntered(MouseEvent e) {}

    @Override
    public void mouseExited(MouseEvent e) {}

    @Override
    public void mousePressed(MouseEvent e) {}

    @Override
    public void mouseReleased(MouseEvent e) {}

    public static void main(String[] args) {
        String patient = PatientScrollPane.getPatient();

        System.out.println("Chosen patient: " + patient);
    }
}

（我试图从高处和低处寻找类似问题的解决方案，但它太笼统而无法找到。）

Answer 1

只要你的 JFrame 存在，事件调度线程就会继续运行，并且会保持 JVM 活动，因为 JFrame 是一个顶级窗口启动一个非守护线程。

更多详情，请关注here。

例如，...

import javax.swing.JDialog;
import javax.swing.JFrame;

public class DialogAndDaemons {
   public static void main(String[] args) {
      JFrame frame = new JFrame();

      JDialog dialog = new JDialog(frame, "Dialog");
      dialog.pack();
      dialog.setLocationRelativeTo(null);
      dialog.setVisible(true);
   }
}

Answer 2

在dialog.dispose();之后，使用System.exit(0);