java - 在实例化自身内部的类后，出现 StackOverflowError

Question

我在此类的第 12 行和第 65 行收到一个 StackOverflowError:

package studInfoAndSubj;    // Information Window 

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;


public class StudInfo extends JFrame
{       
    // This Class
    private StudInfo studInfo = new StudInfo(); // this is Line 12

    // Subjects Window Class
    private StudSubj studSubj = new StudSubj();

    // Labels
    private JLabel nameL = new JLabel("Student Name: ", SwingConstants.CENTER);
    private JLabel snameL = new JLabel("(Surname)", SwingConstants.CENTER);
    private JLabel fnameL = new JLabel("(First Name)", SwingConstants.CENTER);
    private JLabel mnameL = new JLabel("(Middle Name)", SwingConstants.CENTER);
    private JLabel courseL = new JLabel("Course: ", SwingConstants.CENTER);
    private JLabel yearL = new JLabel("Year: ", SwingConstants.CENTER);
    private JLabel semesterL = new JLabel("Semester: ", SwingConstants.CENTER);

    // Text Fields
    private JTextField snameTF = new JTextField(10);
    private JTextField fnameTF = new JTextField(10);
    private JTextField mnameTF = new JTextField(10);

    // Text Value Handlers
    private String snameS, fnameS, mnameS, courseS, yearS, semesterS;

    // Buttons
    private JButton nextB = new JButton("Next");
    private JButton cancelB = new JButton("Cancel");
    private NextButtonHandler nextBH = new NextButtonHandler();
    private CancelButtonHandler cancelBH = new CancelButtonHandler();

    // Layouts ((components + rows - 1) / rows)
    private Container pane = getContentPane();
    private Container one = new JPanel(new GridLayout(0, 6));

    // Combo Boxes
    private String[] course = {"BSIT"};
    private String[] year = {"I"};
    private String[] semester = {"1ST", "2ND"};
    private JComboBox<String> courseCB = new JComboBox<>(course);
    private JComboBox<String> yearCB = new JComboBox<>(year);
    private JComboBox<String> semesterCB = new JComboBox<>(semester);

    // Spaces
    private JLabel blank1 = new JLabel(""); 
    private JLabel blank2 = new JLabel("");
    private JLabel blank3 = new JLabel("");
    private JLabel blank4 = new JLabel("");
    private JLabel blank5 = new JLabel("");
    private JLabel blank6 = new JLabel("");
    private JLabel blank7 = new JLabel("");

    // Window Size
    private static final int WIDTH = 1000;
    private static final int HEIGHT = 250;

    public StudInfo() // and this is line 65
    {
        DefaultListCellRenderer dlcr1 = new DefaultListCellRenderer(); 
        dlcr1.setHorizontalAlignment(DefaultListCellRenderer.CENTER); 
        courseCB.setRenderer(dlcr1);
        yearCB.setRenderer(dlcr1);
        semesterCB.setRenderer(dlcr1);
        snameTF.setHorizontalAlignment(JTextField.CENTER);
        fnameTF.setHorizontalAlignment(JTextField.CENTER);
        mnameTF.setHorizontalAlignment(JTextField.CENTER);
        snameL.setVerticalAlignment(SwingConstants.TOP);
        fnameL.setVerticalAlignment(SwingConstants.TOP);
        mnameL.setVerticalAlignment(SwingConstants.TOP);

        nextB.addActionListener(nextBH);
        cancelB.addActionListener(cancelBH);

        Border border1 = BorderFactory.createLineBorder(Color.BLUE, 1);
        courseL.setBorder(border1);
        yearL.setBorder(border1);
        semesterL.setBorder(border1);

        pane.add(one);
        one.add(blank1);
        one.add(nameL);                         
        one.add(snameTF);
        one.add(fnameTF);
        one.add(mnameTF);
        one.add(blank2);
        one.add(blank3);
        one.add(blank4);
        one.add(snameL);
        one.add(fnameL);
        one.add(mnameL);
        one.add(blank5);
        one.add(courseL);
        one.add(courseCB);
        one.add(yearL);
        one.add(yearCB);
        one.add(semesterL);
        one.add(semesterCB);
        one.add(blank6);
        one.add(blank7);
        one.add(cancelB);
        one.add(nextB);

        setTitle("Student Information");
        setSize(WIDTH, HEIGHT);
        setLocationRelativeTo(null);
        setVisible(true);
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }

    public String getSemValue()
    {
        return semesterS;
    }

    public String[] getSemCBValue()
    {
        return semester;
    }

    private class NextButtonHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            snameS = snameTF.getText();
            fnameS = fnameTF.getText();
            mnameS = mnameTF.getText();
            courseS = courseCB.getSelectedItem().toString();
            yearS = yearCB.getSelectedItem().toString();
            semesterS = semesterCB.getSelectedItem().toString();

            studInfo.setVisible(false);
            studSubj.setVisible(true);

        }

    }

    private class CancelButtonHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            System.exit(0);

        }

    }

public static void main(String[] args) 
{
    StudInfo studInfo = new StudInfo();
}

}

这是我的另一个类:

package studInfoAndSubj;    // Subjects Window

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;


public class StudSubj extends JFrame
{       
    // This class
    private StudSubj studSubj = new StudSubj();

    // Information Window Class
    private StudInfo studInfo = new StudInfo();

    // Labels
    private JLabel addSubjL = new JLabel("Add Subject: ", SwingConstants.CENTER);

    // Buttons
    private JButton doneB = new JButton("Done");
    private JButton backB = new JButton("Back");
    private DoneButtonHandler doneBH = new DoneButtonHandler();
    private BackButtonHandler backBH = new BackButtonHandler();

    // Text Value Handlers
    private String semesterS = studInfo.getSemValue();
    private String[] semester = studInfo.getSemCBValue();
    private int selectedSubj;
    private String selectedSubjTime;

    // Subject Lists
    private String[] sem1Subj = {"College Algebra\nMWF\n12:00PM-1:00PM", 
                "Communication Arts 1\nMWF\n9:00AM-10:00AM", 
                "Information Technology Fundamentals - Lec\nTTH\n7:30AM-8:30AM", 
                "Information Technology Fundamentals - Lab\nT\n9:00AM-12:00PM", 
                "Programming 1\nMWF\n7:00AM-9:00AM"};
    private String[] sem1AddSubj = {"", "Filipino Christian Living\nMWF\n7:00AM-9:00AM", 
                "Foundation of Physical Education\nTH\n10:00AM-12:00PM", 
                "Komunikasyon sa Akademikong Filipino\nMWF\n9:00AM-10:00AM"};
    private String[] sem2Subj = {"Trigonometry\nMWF\n7:00AM-8:00AM", 
                "Communication Arts 2\nTTH\n9:00AM-10:30AM", 
                "Programming 2\nMWF\n9:00AM-11:00AM", 
                "Database Management Systems\nMWF\n8:00AM-9:00AM", 
                "Network Management\nTTH\n7:30AM-9:00AM"};
    private String[] sem2AddSubj = {"", "Environmental Science\nMWF\n8:00AM-9:00AM", 
                "Social Dances\nM\n12:00PM-2:00PM", 
                "General Psychology\nT\n12:00PM-1:00PM"};

    // Subject Time
    private String[] sem1SubjTime = {"MWF12:00PM-1:00PM", "MWF9:00AM-10:00AM", "TTH7:30AM-8:30AM", 
                "T9:00AM-12:00PM", "MWF7:00AM-9:00AM"};
    private String[] sem1AddSubjTime = {"", "MWF7:00AM-9:00AM", "TH10:00AM-12:00PM", "MWF9:00AM-10:00AM"};
    private String[] sem2SubjTime = {"MWF7:00AM-8:00AM", "TTH9:00AM-10:30AM", "MWF9:00AM-11:00AM", 
                "MWF8:00AM-9:00AM", "TTH7:30AM-9:00AM"};
    private String[] sem2AddSubjTime = {"", "MWF8:00AM-9:00AM", "M12:00PM-2:00PM", "T12:00PM-1:00PM"};

    // Layouts ((components + rows - 1) / rows)
    private Container pane = getContentPane();
    private Container two = new JPanel(new GridLayout(0, 2));

    // Combo Boxes
    private JComboBox<String> sem1AddSubjCB = new JComboBox<>(sem1AddSubj);
    private JComboBox<String> sem2AddSubjCB = new JComboBox<>(sem2AddSubj);

    // Window Size
    private static final int WIDTH = 1000;
    private static final int HEIGHT = 250;

    public StudSubj() 
    {
        DefaultListCellRenderer dlcr2 = new DefaultListCellRenderer(); 
        dlcr2.setHorizontalAlignment(DefaultListCellRenderer.CENTER); 
        sem1AddSubjCB.setRenderer(dlcr2);
        sem2AddSubjCB.setRenderer(dlcr2);

        doneB.addActionListener(doneBH);
        backB.addActionListener(backBH);

        // 1st Semester Subjects
        JLabel sem1Subj1 = new JLabel(sem1Subj[0]);
        JLabel sem1Subj2 = new JLabel(sem1Subj[1]);
        JLabel sem1Subj3 = new JLabel(sem1Subj[2]);
        JLabel sem1Subj4 = new JLabel(sem1Subj[3]);
        JLabel sem1Subj5 = new JLabel(sem1Subj[4]);

        // 2nd Semester Subjects
        JLabel sem2Subj1 = new JLabel(sem2Subj[0]);
        JLabel sem2Subj2 = new JLabel(sem2Subj[1]);
        JLabel sem2Subj3 = new JLabel(sem2Subj[2]);
        JLabel sem2Subj4 = new JLabel(sem2Subj[3]);
        JLabel sem2Subj5 = new JLabel(sem2Subj[4]);

        Border border2 = BorderFactory.createLineBorder(Color.BLUE, 1);
        sem1Subj1.setBorder(border2);   sem2Subj1.setBorder(border2);
        sem1Subj2.setBorder(border2);   sem2Subj2.setBorder(border2);
        sem1Subj3.setBorder(border2);   sem2Subj3.setBorder(border2);
        sem1Subj4.setBorder(border2);   sem2Subj4.setBorder(border2);
        sem1Subj5.setBorder(border2);   sem2Subj5.setBorder(border2);
        addSubjL.setBorder(border2);

        pane.add(two);

        if(semesterS.equals(semester[0]))
        {
            setTitle("(BSIT - I - 1st Semester) List Of Subjects");
            two.add(sem1Subj1);
            two.add(sem1Subj2);
            two.add(sem1Subj3);
            two.add(sem1Subj4);
            two.add(sem1Subj5);
            two.add(addSubjL);
            two.add(sem1AddSubjCB);

        }else if(semesterS.equals(semester[1]))
        {
            setTitle("(BSIT - I - 2nd Semester) List Of Subjects");
            two.add(sem2Subj1);
            two.add(sem2Subj2);
            two.add(sem2Subj3);
            two.add(sem2Subj4);
            two.add(sem2Subj5);
            two.add(addSubjL);
            two.add(sem2AddSubjCB);

        }

            two.add(backB);
            two.add(doneB);

            setSize(WIDTH, HEIGHT);
            setLocationRelativeTo(null);
            setResizable(false);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);


        }

        private class DoneButtonHandler implements ActionListener
        {
            public void actionPerformed(ActionEvent e)
            {
                int ctr;

                if(semesterS.equals(semester[0]))
                {
                    selectedSubj = sem1AddSubjCB.getSelectedIndex();
                    selectedSubjTime = sem1AddSubj[selectedSubj];

                    for(ctr = 0; ctr <= sem1AddSubj.length; ctr++)
                    {
                        if(selectedSubjTime.equals(sem1AddSubjTime[ctr]))
                        {
                            JOptionPane.showMessageDialog(null, "Choosen Subject has same time with the others!", "Error", 0);

                        }else{
                            sem1AddSubjCB.getSelectedItem();

                        }

                    }

                }else if(semesterS.equals(semester[1]))
                {
                    selectedSubj = sem2AddSubjCB.getSelectedIndex();
                    selectedSubjTime = sem2AddSubj[selectedSubj];

                    for(ctr = 0; ctr <= sem1AddSubj.length; ctr++)
                    {

                        if(selectedSubjTime.equals(sem2AddSubjTime[ctr]))
                        {
                            JOptionPane.showMessageDialog(null, "Choosen Subject has same time with the others!", "Error", 0);

                        }else{
                            sem2AddSubjCB.getSelectedItem();

                        }
                    }

                }
            }   
        }

        private class BackButtonHandler implements ActionListener
        {
            public void actionPerformed(ActionEvent e)
            {
                studSubj.setVisible(false);
                studInfo.setVisible(true);

            }

        }


public static void main(String[] args) 
{
    StudSubj studSubj = new StudSubj();
}

}

当我运行main时出现此错误:

Exception in thread "main" java.lang.StackOverflowError at sun.awt.Win32GraphicsConfig.getBounds(Native Method) at sun.awt.Win32GraphicsConfig.getBounds(Unknown Source) at java.awt.Window.init(Unknown Source) at java.awt.Window.(Unknown Source) at java.awt.Frame.(Unknown Source) at java.awt.Frame.(Unknown Source) at javax.swing.JFrame.(Unknown Source) at studInfoAndSubj.StudInfo.(StudInfo.java:65) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12) at studInfoAndSubj.StudInfo.(StudInfo.java:12)

为什么会发生这种情况？我可以修复它吗？

Answer 1

这一行:

private StudInfo studInfo = new StudInfo();

从main调用:

StudSubj studSubj = new StudSubj();

创建一个新的 StudInfo 对象，该对象具有相同类型的字段。

当创建 StudInfo 的第一个实例时，其他实例也会被实例化。该还有一个实例化另一个 StudInfo 的字段，依此类推...

如果没有抛出 StackOverflowError，这种情况将永远持续下去。
您需要避免创建类本身的对象作为成员或字段。