Java编译中未经检查或不安全的操作错误？

Question

我正在完成学校的实验任务，并且在编译时出现此错误。该程序运行良好，有点想修复导致错误的原因。程序代码和完整的错误如下。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。

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);
        }
}

Answer 1

这意味着Java编译器已经注意到您的代码存在一些潜在的不安全问题，并警告您。这些问题通常非常琐碎，您可以继续进行下去。特别是因为这是学校的工作。但是要发现问题，您应该使用再次编译：javac -Xlint:unchecked Lab8.java如编译器所说。

该文件中的问题是您尚未指定JComboBox和JList处理的对象的类型。由于您只处理JComboBox和JList中的字符串，因此应指定它。阅读上的Java泛型和这个以获取更多信息。

更改

String[] ageRanges = {"Under 20", "20-29", "30-39", "40-49", "50-59", "60 and Above"};
JComboBox jcbo = new JComboBox(ageRanges);

至

String[] ageRanges = {"Under 20", "20-29", "30-39", "40-49", "50-59", "60 and Above"};
JComboBox<String> jcbo = new JComboBox<String>(ageRanges);

还要更改：

p2.add(new JComboBox(ageRanges), BorderLayout.CENTER);
p2.setBorder(new TitledBorder("Passenger Name & Age Range"));

至

p2.add(new JComboBox<String>(ageRanges), BorderLayout.CENTER);
p2.setBorder(new TitledBorder("Passenger Name & Age Range"));

终于改变

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

至

//Create listbox panel.
JPanel p3 = new JPanel();
p3.setLayout(new GridLayout(1, 0));
p3.add(new JList<String>(destination));

编辑：

不建议将其用于生产代码，但要绕过这些警告，请使用：

@SuppressWarnings("unchecked")

只需在进行不安全操作的任何方法之上添加此代码即可。例如，我认为您可以将其放在此代码中的main方法之上，如下所示：

@SuppressWarnings("unchecked") 
public static void main(String[] args) {
...

这样可以消除警告。