类文件名中的 $1 是什么？

java anonymous-class javac

2022-08-31 14:10:40

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet>dir
 Volume in drive C has no label.
 Volume Serial Number is 2041-64E7

 Directory of C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet

2009-07-02  23:54              .
2009-07-02  23:54              ..
2004-09-06  14:57               582 WelcomeApplet.html
2004-09-06  15:04             1,402 WelcomeApplet.java
               2 File(s)          1,984 bytes
               2 Dir(s)   2,557,210,624 bytes free

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet>javac WelcomeApplet.java

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet>dir
 Volume in drive C has no label.
 Volume Serial Number is 2041-64E7

 Directory of C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet

2009-07-02  23:54              .
2009-07-02  23:54              ..
2009-07-02  23:54               975 WelcomeApplet$1.class
2009-07-02  23:54             1,379 WelcomeApplet.class
2004-09-06  14:57               582 WelcomeApplet.html
2004-09-06  15:04             1,402 WelcomeApplet.java
               4 File(s)          4,338 bytes
               2 Dir(s)   2,557,202,432 bytes free

C:\Program Files\Java\jdk1.6.0_05\CoreJava\v1\v1ch2\WelcomeApplet>

以下是该 Java 文件的内容：

/**
   @version 1.21 2002-06-19
   @author Cay Horstmann
*/

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

public class WelcomeApplet extends JApplet
{
   public void init()
   {
      setLayout(new BorderLayout());

      JLabel label = new JLabel(getParameter("greeting"), SwingConstants.CENTER);
      label.setFont(new Font("Serif", Font.BOLD, 18));
      add(label, BorderLayout.CENTER);

      JPanel panel = new JPanel();

      JButton cayButton = new JButton("Cay Horstmann");
      cayButton.addActionListener(makeURLActionListener(
         "http://www.horstmann.com"));
      panel.add(cayButton);

      JButton garyButton = new JButton("Gary Cornell");
      garyButton.addActionListener(makeURLActionListener(
         "mailto:gary@thecornells.com"));
      panel.add(garyButton);

      add(panel, BorderLayout.SOUTH);
   }

   private ActionListener makeURLActionListener(final String u)
   {
      return new
         ActionListener()
         {
            public void actionPerformed(ActionEvent event)
            {
               try
               {
                  getAppletContext().showDocument(new URL(u));
               }
               catch(MalformedURLException e) 
               { 
                  e.printStackTrace(); 
               }
            }
         };
   }
}

答案 1

这些是保存匿名内部类的文件。.class

在您的示例中，包含一个顶级类（称为）和一个匿名内部类，它们将存储在中。WelcomeApplet.javaWelcomeAppletWelcomeApplet$1.class

请注意，保存匿名内部类的文件的确切名称未标准化，可能会有所不同。但在实践中，除了这里描述的方案之外，我还没有看到任何其他方案。

的值特定主体也是匿名内部类：enum

枚举常量的可选类体隐式定义了一个匿名类声明（§15.9.5），该声明扩展了立即封闭的枚举类型。

答案 2

$1 是您在文件中定义的匿名内部类。WelcomeApplet.java

例如：编译

public class Run {
    public static void main(String[] args) {
        System.out.println(new Object() {
            public String toString() {
                return "77";
            }
        });
    }
    private class innerNamed {
    }
}

将导致和正在生成Run.classRun$1.classRun$innerNamed.class