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Java枚举的原理是什么？

王林

发布： 2023-04-20 22:37:06

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1、枚举是继承了抽象类Enum的类。

Season extends java.lang.Enum<Season>

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2、通过一段静态代码块初始化枚举。

  static {};
    descriptor: ()V
    flags: ACC_STATIC
    Code:
      stack=4, locals=0, args_size=0
         0: new           #4                  // class io/github/yehongzhi/user/redisLock/Season
         3: dup
         4: ldc           #7                  // String SPRING
         6: iconst_0
         7: invokespecial #8                  // Method "<init>":(Ljava/lang/String;I)V
        10: putstatic     #9                  // Field SPRING:Lio/github/yehongzhi/user/redisLock/Season;
        13: new           #4                  // class io/github/yehongzhi/user/redisLock/Season
        16: dup
        17: ldc           #10                 // String SUMMER
        19: iconst_1
        20: invokespecial #8                  // Method "<init>":(Ljava/lang/String;I)V
        23: putstatic     #11                 // Field SUMMER:Lio/github/yehongzhi/user/redisLock/Season;
        26: new           #4                  // class io/github/yehongzhi/user/redisLock/Season
        29: dup
        30: ldc           #12                 // String AUTUMN
        32: iconst_2
        33: invokespecial #8                  // Method "<init>":(Ljava/lang/String;I)V
        36: putstatic     #13                 // Field AUTUMN:Lio/github/yehongzhi/user/redisLock/Season;
        39: new           #4                  // class io/github/yehongzhi/user/redisLock/Season
        42: dup
        43: ldc           #14                 // String WINTER
        45: iconst_3
        46: invokespecial #8                  // Method "<init>":(Ljava/lang/String;I)V
        49: putstatic     #15                 // Field WINTER:Lio/github/yehongzhi/user/redisLock/Season;
        52: iconst_4
        53: anewarray     #4                  // class io/github/yehongzhi/user/redisLock/Season
        56: dup
        57: iconst_0
        58: getstatic     #9                  // Field SPRING:Lio/github/yehongzhi/user/redisLock/Season;
        61: aastore
        62: dup
        63: iconst_1
        64: getstatic     #11                 // Field SUMMER:Lio/github/yehongzhi/user/redisLock/Season;
        67: aastore
        68: dup
        69: iconst_2
        70: getstatic     #13                 // Field AUTUMN:Lio/github/yehongzhi/user/redisLock/Season;
        73: aastore
        74: dup
        75: iconst_3
        76: getstatic     #15                 // Field WINTER:Lio/github/yehongzhi/user/redisLock/Season;
        79: aastore
        80: putstatic     #1                  // Field $VALUES:[Lio/github/yehongzhi/user/redisLock/Season;
        83: return

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这段静态代码块的作用就是生成四个静态常量字段的值，还生成了$VALUES字段，用于保存枚举类定义的枚举常量。

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3、关于values()方法，这是一个静态方法，作用是返回该枚举类的数组，底层实现原理，其实是这样的。

public static io.github.yehongzhi.user.redisLock.Season[] values();
    Code:
       0: getstatic     #1                  // Field $VALUES:[Lio/github/yehongzhi/user/redisLock/Season;
       3: invokevirtual #2                  // Method "[Lio/github/yehongzhi/user/redisLock/Season;".clone:()Ljava/lang/Object;
       6: checkcast     #3                  // class "[Lio/github/yehongzhi/user/redisLock/Season;"
       9: areturn

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