学生/研究生课程中的经理类问题

Question

本项目的目标是创建四个类：Student 类、GradStudent 类、Manager 类和 GUI 类。在 GUI 中有两个单选按钮：一个用于学生，一个用于研究生。根据选择哪一个，Manager 类应该负责通过使用两个数组来创建和存储 Student 或 GradStudent 对象。我的所有课程都已编程，但是当我选择任一单选按钮时，我在 Manager.getLastGradStudent 中出现错误，这反过来又在我的 JRBListener 课程中给我一个错误。我将在下面发布 GUI 和管理器类。任何帮助将不胜感激！

经理类：

public class Manager {
    private Student[] students = new Student[50];
    private int counter1 = 0;

    private GradStudent[] gradStudents = new GradStudent[50];
    private int counter2 = 0;

    public Manager() {

    }

    public void addStudent(String name, String address, String balance, String major) {
        Student student1 = new Student(name, address, balance, major);
        students[counter1] = student1;
                counter1++;
    }
    public String getLastStudent() {
        return "Student added: " + students[counter1-1] +"\n";
    }

    public void addGradStudent(String name, String address, String balance, String major) {
        GradStudent student2 = new GradStudent(name, address, balance, major);
        gradStudents[counter2] = student2;
                counter2++;
    }
    public String getLastGradStudent() {
        return "Graduate Student added: " + gradStudents[counter2-1] +"\n";
    }
}

GUI 类：

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JRadioButton;
import javax.swing.ButtonGroup;


public class GUI extends JFrame {
    private JRadioButton jrbStudent = new JRadioButton("Student");
    private JRadioButton jrbGraduate = new JRadioButton("Graduate");
    private JTextField name = new JTextField(20);
    private JTextField address = new JTextField(20);
    private JTextField balance = new JTextField(20);
    private JTextField major = new JTextField(20);
    private JButton jbtSubmit = new JButton("Submit");
    private JTextArea echoStudent = new JTextArea();
    private Manager m1 = new Manager();

    public GUI() {

        // Creates panel P1 and adds the components
        JPanel p1 = new JPanel(new GridLayout(7, 1));
        p1.add(new JLabel("Name: "));
        p1.add(name);
        p1.add(new JLabel("Address: "));
        p1.add(address);
        p1.add(new JLabel("Balance: "));
        p1.add(balance);
        p1.add(new JLabel("Major: "));
        p1.add(major);
        p1.add(jrbStudent);
        p1.add(jrbGraduate);
        p1.add(new JLabel("Submit Button: "));
        p1.add(jbtSubmit);
        p1.add(new JLabel("Submitted Text: "));

        // Creates a radio-button group to group both buttons
        ButtonGroup group = new ButtonGroup();
        group.add(jrbStudent);
        group.add(jrbGraduate);

        // Adds the panel and text area to the frame
        add(p1);
        p1.add(echoStudent);
        echoStudent.setEditable(false);

        // Creates a listener and registers it with the submit button
        SubmitListener l1 = new SubmitListener();
        jbtSubmit.addActionListener(l1);

        // Creates a listener and registers it with the radio buttons
        JRBListener l2 = new JRBListener();
        jrbStudent.addActionListener(l2);
        jrbGraduate.addActionListener(l2);
    }

    // Class to handle the submit button
    class SubmitListener implements ActionListener {
        public void actionPerformed(ActionEvent a) {
            Student[] students = new Student[50];
            int arrayLocation = 0;

            Student student1 = new Student(name.getText(), address.getText(),
                    balance.getText(), major.getText());
            // Checks remaining array space
            if (arrayLocation < 50) {
                students[arrayLocation] = student1;
                ++arrayLocation;
            }
            // Echos back entered text while storing the previous text
            echoStudent.setText(echoStudent.getText() + "\n"
                    + student1.toString());
        }
    }

    // Class to handle the radio buttons
    class JRBListener implements ActionListener {
        public void actionPerformed(ActionEvent b) {
            if(b.getSource() == jrbStudent)
                m1.addStudent(name.getText(), address.getText(), balance.getText(), major.getText());
            echoStudent.setText("Created Student: \n" + m1.getLastStudent());

            if(jrbGraduate.isSelected())
                m1.addGradStudent(name.getText(), address.getText(), balance.getText(), major.getText());
            echoStudent.setText("Created Graduate Student: \n" + m1.getLastGradStudent());
        }
    }

    public static void main(String[] args) {
        GUI frame = new GUI();
        frame.setTitle("Information Interface");
        frame.setSize(1200, 900);
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

    }

}

我收到的错误：

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: -1
    at Manager.getLastGradStudent(Manager.java:28)
    at GUI$JRBListener.actionPerformed(GUI.java:93)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.JToggleButton$ToggleButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

您的代码中的问题是您没有设置任何括号来定义 JRBListener.actionPerformed() 方法中的 if 范围。如果没有设置括号，则只有 if-condition 之后的下一行被认为在范围内。因此，在您的情况下，无论是否添加了学生，程序都将始终尝试声明“已添加学生！”消息 :-) 这只有在您实际添加一个学生时才有意义：

public void actionPerformed(ActionEvent b) {
       if (b.getSource() == jrbStudent) {
           m1.addStudent(name.getText(), address.getText(), balance.getText(), major.getText());
           echoStudent.setText("Created Student: \n" + m1.getLastStudent());
       }

       if (jrbGraduate.isSelected()) {
            m1.addGradStudent(name.getText(), address.getText(), balance.getText(), major.getText());
            echoStudent.setText("Created Graduate Student: \n" + m1.getLastGradStudent());
       }
}