java - JComboBox - 越界异常

Question

我有一个小问题。我正在尝试将登录名从数据库导入到 vector ，然后将该 vector 用于 JComboBox。我下载登录名的方法:

public void loginReader (Vector<String> loginy, String tableName)
{
    String query = "select login from " + tableName;

    try {

        Statement statement = mConnection.createStatement();
        ResultSet rs = statement.executeQuery(query);
        while (rs.next()) 
            {
             Vector<String> vstring = new Vector<String>();

                vstring.add(rs.getString("login"));


                loginy.addAll(vstring);
            }
        } catch (SQLException e)
            {
                e.printStackTrace();

            }
}

这是在DatabaseManagement 类中。我创建了另一个类(GUI)，这就是 JComboBox。为什么它不起作用？

package DataBase_Hospital;



 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.text.ParseException;
 import java.util.Properties;
 import java.util.Vector;

 import javax.swing.ImageIcon;
 import javax.swing.JButton;
 import javax.swing.JComboBox;
 import javax.swing.JFrame;
 import javax.swing.JLabel;
 import javax.swing.JScrollPane;
 import javax.swing.JTextArea;
 import javax.swing.JTextField;


 public class Message extends JFrame implements ActionListener {



JButton SEND_MESSAGE;
JButton READ_MESSAGE;
public JLabel background;

JLabel NAME_LABEL;

JTextField NAME_FIELD;

JTextArea DATABASE_FIELD;
static Vector<String> loginy = new Vector<String>();

private static DatabaseManagement DATABASE;

public Message() {



    setSize(290, 500);
    setTitle("Message Panel");


    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
    JLabel background=new JLabel(new ImageIcon("/Users/Dominik/Desktop/messageFrame.png"));
    add(background);


    DATABASE_FIELD = new JTextArea(3,3);
    JScrollPane scrollPane = new JScrollPane(DATABASE_FIELD);
    scrollPane.setBounds(45, 50, 200, 200);
    background.add(scrollPane);
    DATABASE_FIELD.setEditable(true);


    NAME_LABEL = new JLabel("Odbiorca :");
    NAME_LABEL.setBounds(40, 380, 140, 20);
    background.add(NAME_LABEL);

    SEND_MESSAGE = new JButton();
    SEND_MESSAGE.setIcon(new ImageIcon("/Users/Dominik/Desktop/sendMail.jpg"));
    SEND_MESSAGE.setBounds(75, 270, 60, 60);
    background.add(SEND_MESSAGE);
    SEND_MESSAGE.addActionListener(this);
    SEND_MESSAGE.setToolTipText("Send message");

    READ_MESSAGE = new JButton();
    READ_MESSAGE.setIcon(new ImageIcon("/Users/Dominik/Desktop/jwj.png"));
    READ_MESSAGE.setBounds(150, 270, 60, 60);
    background.add(READ_MESSAGE);
    READ_MESSAGE.addActionListener(this);
    READ_MESSAGE.setToolTipText("Read message");


  JComboBox loginList = new JComboBox(loginy);
  loginList.setSelectedIndex(loginy.capacity());
  loginList.addActionListener(this);
  loginList.setBounds(145, 380, 100, 20);
  background.add(loginList);

}

public static void main(String[] args) {

    Message window = new Message();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setVisible(true);
    DATABASE.loginReader(loginy,"uzytkownicy");
}

public void actionPerformed(ActionEvent e) 
{
    Object EVENT_SOURCE = e.getSource();
    DATABASE = new DatabaseManagement("pacjent");

    if (EVENT_SOURCE == SEND_MESSAGE) 
    {
        DATABASE.sendMessage(DATABASE_FIELD.getText(), "uzytkownicy", NAME_FIELD.getText()) ;
    }

}
}

Answer 1

使用空的 Vector 创建 JComboBox 后，将 selectedIndex 设置为 loginy.capacity () 。问题在于，虽然 Vector 的容量为 10(如 JavaDoc for the default constructor 中所述)，但它的实际大小为 0。因此会出现 ArrayOutOfBoundsException。在设置 JComboBox 的选定索引之前，您应该检查 Vector 的大小。