我正在完成学校的实验作业，在编译时遇到此错误。程序运行良好，bit 想修复导致错误的原因。程序代码和完整错误如下。一如既往的感谢!

错误: 注意:F:\Java\Lab 8\Lab8.java 使用未经检查或不安全的操作。 注意:使用 -Xlint:unchecked 重新编译以获取详细信息。

代码:

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


   public class Lab8 extends JFrame {
       public Lab8()
           {

           // Create an array of Strings for age ranges
           String[] ageRanges = {"Under 20", "20-29", "30-39", "40-49", "50-59", "60 and Above"};
           JComboBox jcbo = new JComboBox(ageRanges);

           // Create an array of String destinations
           String[] destination = {"Mercury", "Venus", "Moon", "Mars", "Jupiter / Europa", "Saturn / Triton", "Pluto + Sharon"};
           JList jlst = new JList();

           // Declare radio buttons
           JRadioButton jrbMonday, jrbTuesday, jrbWednesday, jrbThursday, jrbFriday;

           // Create a textfield
           JTextField jMsg = new JTextField(10);


           // Create panel to hold label and textbox.
           JPanel p1 = new JPanel();
           p1.setLayout(new BorderLayout(5,0));
           p1.add(new JLabel("Name: "), BorderLayout.WEST);
           p1.add(new JTextField(20), BorderLayout.CENTER);
           jMsg.setHorizontalAlignment(JTextField.LEFT);


           // Create combobox panel.
           JPanel p2 = new JPanel();
           p2.setLayout(new GridLayout(2,0,5,5));
           p2.add(p1, BorderLayout.NORTH);
           p2.add(new JComboBox(ageRanges), BorderLayout.CENTER);
               p2.setBorder(new TitledBorder("Passenger Name & Age Range"));


           //Create listbox panel.
           JPanel p3 = new JPanel();
           p3.setLayout(new GridLayout(1, 0));
           p3.add(new JList(destination));
               p3.setBorder(new TitledBorder("Destinations"));


           // Create a new panel to hold radio buttons.
               JPanel r1 = new JPanel();
           r1.setLayout(new GridLayout(3,2));
           r1.add(jrbMonday = new JRadioButton("Monday"));
           r1.add(jrbTuesday = new JRadioButton("Tuesday"));
           r1.add(jrbWednesday = new JRadioButton("Wednesday"));
           r1.add(jrbThursday = new JRadioButton("Thursday"));
           r1.add(jrbFriday = new JRadioButton("Friday"));
           r1.setBorder(new TitledBorder("Departure Days"));


           // Create a radio button group to group five buttons
           ButtonGroup group = new ButtonGroup();
           group.add(jrbMonday);
           group.add(jrbTuesday);
           group.add(jrbWednesday);
           group.add(jrbThursday);
           group.add(jrbFriday);


           // Create grid to hold contents
           JPanel pMain = new JPanel();
           pMain.setLayout(new BorderLayout(5,0));
           add(r1, BorderLayout.CENTER);
           add(p2, BorderLayout.NORTH);
           add(p3, BorderLayout. EAST);

}


public static void main(String[] args)
       {
           Lab8 frame = new Lab8();
           frame.pack();
           frame.setTitle("Lab 8 Application");
           frame.setLocationRelativeTo(null); // Center the frame
           frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           frame.setSize(425, 275);
           frame.setVisible(true);
        }
}