java编译中未经检查或不安全的操作错误？ [英] Unchecked or unsafe operations error in java compile?

问题描述

我正在完成学校的实验室作业，并在编译时遇到此错误。程序运行正常，有点想修复导致错误的原因。程序代码和完整错误如下。一如既往地感谢！

I am completing a lab assignment for school and get this error when I compile. The program runs fine, bit would like to fix what is causing the error. The program code and the complete error is below. Thanks as always!

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重新编译：取消选中以获取详细信息。

Error: Note: F:\Java\Lab 8\Lab8.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details.

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);
        }
}

推荐答案

什么这意味着Java编译器已经注意到您的代码可能存在一些不安全的问题并且警告您。这些问题通常非常简单，你可以继续使用它们;特别是因为这是学校的工作。但要找到问题，你应该再次编译： javac -Xlint：unchecked Lab8.java 就像编译器说的那样。

What this means is that the Java compiler has noticed some potentially unsafe issues with your code and is warning you. These issues are normally very trivial and you could carry on with them; especially since this is school work. But to find the issues, you should compile again with: javac -Xlint:unchecked Lab8.java like the compiler says.

此文件中的问题是您尚未指定JComboBox和JList正在处理的对象类型。由于您只处理JComboBox和JList中的字符串，因此您应该指定它。阅读 Java泛型和这个以获取更多信息。

The issues in this file are that you haven't specified the type of object the JComboBox and JList are dealing with. Since you are only dealing with Strings in the JComboBox and JList, you should specify that. Read up on Java generics and this for more information.

更改

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

到

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

同时更改：

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

到

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

最后更改

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

到

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

编辑：

不建议用于生产代码，但绕过这些警告使用：

Not recommended for production code, but to bypass these warnings use:

@SuppressWarnings("unchecked") 

只需在上面添加任何使不安全操作的方法。例如，我认为你可以把它放在你的主要方法上面，如下所示：

Just add this above any method that makes unsafe operations. For instance, I think you could put it above your main method in this code like so:

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

这会抑制警告。

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