Why is <filename> $ 1.class created?

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.classand Enum1$1.classwhen compiling this code. When I comment on a part of the switch, only Enum1.classand are generated Day.class.

What causes the switch to create an additional file Enum1$1.class?

Answer 1

Uses javapfor classes in a 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, switchcalls javacto generate additional static final int[] $SwitchMap$de$lhorn$so$Day;.