What is the principle of Java enumeration?
Apr 20, 2023 pm 10:37 PM1. Enumeration is a class that inherits the abstract class Enum.
Season extends java.lang.Enum<Season>
2. Initialize the enumeration through a static code block.
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
The function of this static code block is to generate the values of four static constant fields, and also generate the $VALUES field, which is used to save the enumeration constants defined by the enumeration class.
3. Regarding the values() method, this is a static method that returns an array of the enumeration class. The underlying implementation principle is actually like this.
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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