java - 线程中的异常 "main"java.lang.IllegalArgumentException : setSelectedIndex: 4 out of bounds

Question

我正在尝试制作一个游戏，但我的代码根本无法工作，我不知道为什么。我是一名经验不足的新手程序员，并且对我的代码感到非常沮丧。我一直在尝试解决这个问题，但没有成功。请帮助我。

public class hello {
    //Int's and things
    static JButton Play = new JButton("<PLAY>");
    static JFrame pane = new JFrame("CIrCUT 0.0.2");
    static JLabel Title = new JLabel("CIrCUT");
    static JLabel none = new JLabel(" ");
    static JPanel panel = new JPanel(new GridLayout(10, 10, 10, 10));
    static JButton Options = new JButton("<OPTIONS>");
    static JPanel panel2 = new JPanel(new GridLayout(10, 10, 10, 10));
    static String b[] = new String[3];
    static int panelLoct = 1;
    JComboBox optionlist = new JComboBox();

    void initialize() {
        b[0] = "High";
        b[1] = "Medium";
        b[2] = "Low";

        //title
        pane.setTitle("CIrCUT 0.0.2");
        //drop down
        optionlist .setModel(new DefaultComboBoxModel(new String[] {"Option", "High", "Medium",  "Low"}));
        optionlist.setSelectedIndex(4);
        optionlist.addActionListener((ActionListener) this);
        //other pane-related things
        if (panelLoct == 1) {
            pane.setLayout(new GridLayout(10, 10));
            panel.setMaximumSize(new Dimension(500, 500));
            pane.setSize(500, 500);
            pane.setMaximumSize(new Dimension(500, 500));
            panel.add(Title);
            panel.add(none);
            panel.add(Play);
            panel.add(Options);
            panel2.add(optionlist);
            Play.setSize(new Dimension(500, 450));
            pane.setLocation(500, 50);
            pane.setBackground(Color.lightGray);
            pane.setContentPane(panel);
            pane.pack();
            pane.setMinimumSize(new Dimension(500, 500));
            pane.setContentPane(panel);
            OptionButtonHandler cbHandler = new OptionButtonHandler();
            Options.addActionListener(cbHandler);
            pane.setVisible(true);
        }
    }

    public void windowClosing(WindowEvent e) {
        System.exit(0);
    }

    private static class OptionButtonHandler implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            pane.remove(panel);
            pane.add(panel2);
        }
    }

    public void actionPerformed(ActionEvent e) {
        JComboBox cb = (JComboBox) e.getSource();
        cb.getSelectedItem();
    }

    public static void main(String args[]) {
        hello a = new hello();
        a.initialize();
    }
}

我认为问题出在 JComboBox 上，但每当我删除它时，我都会收到错误。

编辑

这是错误

at javax.swing.JComboBox.setSelectedIndex(Unknown Source)
at hello.initialize(hello.java:36)
at hello.main(hello.java:81)

Answer 1

JComboBox optionlist = new JComboBox();
optionlist.setSelectedIndex(4);

这将导致异常，因为您正在设置空 JComboBox 的索引。只是不要这样做。在选择索引之前，先用项目填充组合框。

事实上，您在哪里向 JComboBox 添加任何项？

请注意，将来如果您对代码生成的异常有疑问，您需要在此处发布实际的异常堆栈跟踪，并为我们指示哪一行抛出异常。