什么意思是带有美元符号和数字.class的java文件名(名称$ 1.class)？

Question

当我编译我的java Enum Day时,它会生成他的Day.class文件和8天$#.class Files,所以我想知道为什么编译器生成8 $#.class而不是7,因为我有7个枚举常量,但是8覆盖注释,我已经知道Dollar.class文件是为每个内部类或枚举常量生成的,但是八个.class文件为它生成了什么呢？

package com.kaissersoft.test.objective.one.three.enums;

public enum Day{
    SUNDAY(01){
    @Override
    public void salute(){
        System.out.println("Today is Sunday");
    }
},
MONDAY(02){
    @Override
    public void salute(){
        System.out.println("Today is Monday");
    } 
},
TUESDAY(03){
    @Override
    public void salute(){
        System.out.println("Today is Tuesday");
    }
},
WEDNESDAY(04){
    @Override 
    public void salute(){
        System.out.println("Today is Wednesday");
    }
},
THURSDAY(05){
    @Override
    public void salute(){
        System.out.println("Today is Thursday");
    }
},
FRIDAY(06){
    @Override
    public void salute(){
        System.out.println("Today is Friday");
    }
},
SATURDAY(07){
    @Override
    public void salute(){
        System.out.println("Today is Saturday");
    }
};

int dayNumber;
Day(final int day){
    dayNumber = day;
}

public int getDayNumber(){
    return dayNumber;
}

@Override
public String toString(){

    switch(this){
        case SUNDAY:
            System.out.println("Sunday("+this.getDayNumber()+")");
            break;
        case MONDAY:
            System.out.println("Monday("+this.getDayNumber()+")");
            break;
        case TUESDAY:
            System.out.println("Tuesday"+this.getDayNumber()+")");
            break;
        case WEDNESDAY:
            System.out.println("Wednesday("+this.getDayNumber()+")");
            break;
        case THURSDAY:
            System.out.println("Thursday("+this.getDayNumber()+")");
            break;
        case FRIDAY:
            System.out.println("Friday("+this.getDayNumber()+")");
            break;
        case SATURDAY:
            System.out.println("Saturday("+this.getDayNumber()+")");
            break;
    }
    return super.toString();
}

//Abstract method to the day Salute
public abstract void salute();
}

它产生了这个:

• Day.class
• 天$ 1.class
• 天$ 2.class
• 天$ 3.class
• 天$ 4.class
• 天$ 5.class
• 天$ 6.class
• 天$ 7.class
• 天$ 8.class

Answer 1

每个 Enum 字面量都会生成一个由 Enum 名称加上枚举字面量索引标识的类，除了 Enum 生成的类之外，后缀为 8 的枚举类是一个名为 SwitchMap 的映射，它是一个维护开关使用的枚举文字索引的引用，如果执行此代码，您可以看到它。

        try{
             Class< ? > c = Class.forName( "com.kaissersoft.test.objective.one.three.enums.Days$8" );

            Field[] fs= c.getDeclaredFields();
            for( Field f: fs ){
           System.out.println( f.toString() );
            }
        }catch( ClassNotFoundException cne){
          cne.printStackTrace();
        }


// Output
static final int[] com.kaissersoft.test.objective.one.three.enums.Days$8.$Switch
Map$com$kaissersoft$test$objective$one$three$enums$Days