why is $1.class generated?

Question

enum Day{ SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}  

class Enum1 {  

  public static void main(String args[]) {  

    Day day=Day.MONDAY;  

    switch(day) {  
      case SUNDAY:   
        System.out.println("sunday");  
        break;  
      case MONDAY:   
        System.out.println("monday");  
        break;  
      default:  
        System.out.println("other day");
    }
  }
}

I see that Enum1.class ,Day.class, and Enum1$1.class when I compile this code. When I comment out the switchcase part only Enum1.class and Day.class are generated.

What in the switchcase is the cause of generating an extra Enum1$1.class file?

`javap -verbose Enum1$1.class` can show you the contents of that class file, which might be a clue. — user253751, Apr 10 '15 at 10:52
see http://stackoverflow.com/questions/1834632/java-enum-and-additional-class-files — Sergey Grinev, Apr 10 '15 at 11:03

score 2 · Accepted Answer · answered Apr 10 '15 at 11:03

Using javap on classes in the package de.lhorn:

Day.class

public final class de.lhorn.so.Day extends java.lang.Enum<de.lhorn.so.Day> {
  public static final de.lhorn.so.Day SUNDAY;
  public static final de.lhorn.so.Day MONDAY;
  public static final de.lhorn.so.Day TUESDAY;
  public static final de.lhorn.so.Day WEDNESDAY;
  public static final de.lhorn.so.Day THURSDAY;
  public static final de.lhorn.so.Day FRIDAY;
  public static final de.lhorn.so.Day SATURDAY;
  public static de.lhorn.so.Day[] values();
  public static de.lhorn.so.Day valueOf(java.lang.String);
  static {};
}

Enum1.class

public class de.lhorn.so.Enum1 {
  public de.lhorn.so.Enum1();
  public static void main(java.lang.String[]);
}

Enum$1.class

class de.lhorn.so.Enum1$1 {
  static final int[] $SwitchMap$de$lhorn$so$Day;
  static {};
}

So the switch causes javac to generate the additional static final int[] $SwitchMap$de$lhorn$so$Day;.

why is $1.class generated?

1 Answers1