Kotlin字节码生成机制详尽分析
通过注解修改Kotlin的class文件名:
对于Kotlin文件在编译之后生成的class文件名默认是有一定规则的,比如:
而其实这个生成字节码的文件名称是可以被改的,之前https://www.cnblogs.com/webor2006/p/11530600.html也提及到,也就是可以用JvmName注解,再来试一下:
然后重新的build一次,再来看一下生成的class文件:
既然可以手动的将编译的字符码文件名给改了,那。。如果两个Kotlin文件都指定同一个名称,会有啥情况发生呢?试试,再来建一个Kotlin文件:
那。。有没有一种机制能将这两个类的内容生成到一个HelloWorld.class,当然有,也就是Kotlin中可以将多个Kotlin文件合并成一个字节码文件,下面来看一下:
接下来再次编译:
居然此时就没报错了,那这个字节码文件中的内容是?跟进去瞅一下:
bogon:kotlin_lecture xiongwei$ javap -c -v com/kotlin/test11/HelloWorld.class Classfile /Users/xiongwei/Documents/workspace/IntelliJSpace/kotlin_lecture/out/production/kotlin_lecture/com/kotlin/test11/HelloWorld.class Last modified 2019-9-20; size 860 bytes MD5 checksum 47cd63b80d95d489afa25bedd346da23 public final class com.kotlin.test11.HelloWorld minor version: 0 major version: 52 flags: ACC_PUBLIC, ACC_FINAL, ACC_SUPER Constant pool: #1 = Utf8 com/kotlin/test11/HelloWorld #2 = Class #1 // com/kotlin/test11/HelloWorld #3 = Utf8 java/lang/Object #4 = Class #3 // java/lang/Object #5 = Utf8 getMystr #6 = Utf8 ()Ljava/lang/String; #7 = Utf8 Lorg/jetbrains/annotations/NotNull; #8 = Utf8 com/kotlin/test11/HelloWorld__HelloKotlin3Kt #9 = Class #8 // com/kotlin/test11/HelloWorld__HelloKotlin3Kt #10 = NameAndType #5:#6 // getMystr:()Ljava/lang/String; #11 = Methodref #9.#10 // com/kotlin/test11/HelloWorld__HelloKotlin3Kt.getMystr:()Ljava/lang/String; #12 = Utf8 setMystr #13 = Utf8 (Ljava/lang/String;)V #14 = NameAndType #12:#13 // setMystr:(Ljava/lang/String;)V #15 = Methodref #9.#14 // com/kotlin/test11/HelloWorld__HelloKotlin3Kt.setMystr:(Ljava/lang/String;)V #16 = Utf8 <set-?> #17 = Utf8 Ljava/lang/String; #18 = Utf8 myPrint #19 = Utf8 ()V #20 = NameAndType #18:#19 // myPrint:()V #21 = Methodref #9.#20 // com/kotlin/test11/HelloWorld__HelloKotlin3Kt.myPrint:()V #22 = Utf8 myPrint2 #23 = Utf8 com/kotlin/test11/HelloWorld__HelloKotlin4Kt #24 = Class #23 // com/kotlin/test11/HelloWorld__HelloKotlin4Kt #25 = NameAndType #22:#19 // myPrint2:()V #26 = Methodref #24.#25 // com/kotlin/test11/HelloWorld__HelloKotlin4Kt.myPrint2:()V #27 = Utf8 Lkotlin/Metadata; #28 = Utf8 mv #29 = Integer 1 #30 = Integer 15 #31 = Utf8 bv #32 = Integer 0 #33 = Integer 3 #34 = Utf8 k #35 = Integer 4 #36 = Utf8 d1 #37 = Utf8 Code #38 = Utf8 LineNumberTable #39 = Utf8 RuntimeInvisibleAnnotations #40 = Utf8 LocalVariableTable #41 = Utf8 RuntimeInvisibleParameterAnnotations #42 = Utf8 RuntimeVisibleAnnotations { public static final java.lang.String getMystr(); descriptor: ()Ljava/lang/String; flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL Code: stack=1, locals=0, args_size=0 0: invokestatic #11 // Method com/kotlin/test11/HelloWorld__HelloKotlin3Kt.getMystr:()Ljava/lang/String; 3: areturn LineNumberTable: line 1: 0 RuntimeInvisibleAnnotations: 0: #7() public static final void setMystr(java.lang.String); descriptor: (Ljava/lang/String;)V flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokestatic #15 // Method com/kotlin/test11/HelloWorld__HelloKotlin3Kt.setMystr:(Ljava/lang/String;)V 4: return LineNumberTable: line 1: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 <set-?> Ljava/lang/String; RuntimeInvisibleParameterAnnotations: 0: 0: #7() public static final void myPrint(); descriptor: ()V flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL Code: stack=0, locals=0, args_size=0 0: invokestatic #21 // Method com/kotlin/test11/HelloWorld__HelloKotlin3Kt.myPrint:()V 3: return LineNumberTable: line 1: 0 public static final void myPrint2(); descriptor: ()V flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL Code: stack=0, locals=0, args_size=0 0: invokestatic #26 // Method com/kotlin/test11/HelloWorld__HelloKotlin4Kt.myPrint2:()V 3: return LineNumberTable: line 1: 0 } RuntimeVisibleAnnotations: 0: #27(#28=[I#29,I#29,I#30],#31=[I#29,I#32,I#33],#34=I#35,#36=[s#8,s#23])
很明显字节码中确实是已经包含HelloKotlin3.kt和HelloKotlin4.kt的内容进行了合并了,既然这俩文件最终会编译成一个字节码,那如果在HelloKotlin4.kt中也定义一个跟HelloKotlin3.kt一样的方法名会有啥反应呢,如下:
比较容易理解,还是将其方法名进行还原,接下来新建一个Java文件来调用一下:
@JvmField:
使用@JvmFiled注解对Kotlin中的属性进行标注时,表示它是一个实例字段(instance filed),Kotlin编译器在处理的时候,将不会给这个字段生成getter/setter。
下面先来新建一个类:
接下来咱们可以使用@JvmField注解,如下:
注上它之后,其实该字段就变为了一个实例字段,Kotlin编译器就不会给该字段生成getter和setter了,下面反编译一下:
那。。没法验证所说的理论了呀,这里换一种思路,从Java调用上面来验证:
当然,实际过程中貌似木有必要使用该注解,一般用getter和setter的较大,做个了解。
伴生对像:
关于它其实在之前https://www.cnblogs.com/webor2006/p/11210181.html已经学习过了,这里从Java调用Kotlin的角度再来看一它:
然后再新建一个Java:
完整调用如下:
好,接下来咱们再用一个@JvmField注解:
此时程序调用就得修改为:
接下来再来看一下在伴生对象中定义方法又是如何调用的,如下:
那在字节码中MyClass2是如何定义的呢?反编译一下,之前反编译乱码了,下面用javap -v来看一下:
bogon:kotlin_lecture xiongwei$ javap -verbose com/kotlin/test11/MyClass2.class Classfile /Users/xiongwei/Documents/workspace/IntelliJSpace/kotlin_lecture/out/production/kotlin_lecture/com/kotlin/test11/MyClass2.class Last modified 2019-9-21; size 770 bytes MD5 checksum b7bf58035d08f2c1f25542b389451e7e Compiled from "HelloKotlin7.kt" public final class com.kotlin.test11.MyClass2 minor version: 0 major version: 52 flags: ACC_PUBLIC, ACC_FINAL, ACC_SUPER Constant pool: #1 = Utf8 com/kotlin/test11/MyClass2 #2 = Class #1 // com/kotlin/test11/MyClass2 #3 = Utf8 java/lang/Object #4 = Class #3 // java/lang/Object #5 = Utf8 <init> #6 = Utf8 ()V #7 = NameAndType #5:#6 // "<init>":()V #8 = Methodref #4.#7 // java/lang/Object."<init>":()V #9 = Utf8 this #10 = Utf8 Lcom/kotlin/test11/MyClass2; #11 = Utf8 <clinit> #12 = Utf8 Companion #13 = Utf8 Lcom/kotlin/test11/MyClass2$Companion; #14 = Utf8 Lkotlin/Metadata; #15 = Utf8 mv #16 = Integer 1 #17 = Integer 15 #18 = Utf8 bv #19 = Integer 0 #20 = Integer 3 #21 = Utf8 k #22 = Utf8 d1 #23 = Utf8 \n\n\ 20:B¢¨ #24 = Utf8 d2 #25 = Utf8 #26 = Utf8 kotlin_lecture #27 = Utf8 com/kotlin/test11/MyClass2$Companion #28 = Class #27 // com/kotlin/test11/MyClass2$Companion #29 = Utf8 (Lkotlin/jvm/internal/DefaultConstructorMarker;)V #30 = NameAndType #5:#29 // "<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V #31 = Methodref #28.#30 // com/kotlin/test11/MyClass2$Companion."<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V #32 = NameAndType #12:#13 // Companion:Lcom/kotlin/test11/MyClass2$Companion; #33 = Fieldref #2.#32 // com/kotlin/test11/MyClass2.Companion:Lcom/kotlin/test11/MyClass2$Companion; #34 = Utf8 HelloKotlin7.kt #35 = Utf8 Code #36 = Utf8 LineNumberTable #37 = Utf8 LocalVariableTable #38 = Utf8 InnerClasses #39 = Utf8 SourceFile #40 = Utf8 RuntimeVisibleAnnotations { public static final com.kotlin.test11.MyClass2$Companion Companion; descriptor: Lcom/kotlin/test11/MyClass2$Companion; flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL public com.kotlin.test11.MyClass2(); descriptor: ()V flags: ACC_PUBLIC Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this Lcom/kotlin/test11/MyClass2; static {}; descriptor: ()V flags: ACC_STATIC Code: stack=3, locals=0, args_size=0 0: new #28 // class com/kotlin/test11/MyClass2$Companion 3: dup 4: aconst_null 5: invokespecial #31 // Method com/kotlin/test11/MyClass2$Companion."<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V 8: putstatic #33 // Field Companion:Lcom/kotlin/test11/MyClass2$Companion; 11: return } InnerClasses: public static final #12= #28 of #2; //Companion=class com/kotlin/test11/MyClass2$Companion of class com/kotlin/test11/MyClass2 SourceFile: "HelloKotlin7.kt" RuntimeVisibleAnnotations: 0: #14(#15=[I#16,I#16,I#17],#18=[I#16,I#19,I#20],#21=I#16,#22=[s#23],#24=[s#10,s#25,s#6,s#12,s#26])
木有乱码了,好,面目就可以揭开了,首先:
所以我们就可以这样来调用:
其实我们可以改变其伴身对象方法的默认规则,就得用下面这个注解了。
@JvmStatic:
在Kotlin中,我们可以将具名对象或是伴生对象中定义的函数注解为@JvmStatic,这样编译器既会在相应对象的类中生成静态方法,也会在对象自身中生成实例方法。下面来尝试一下:
此时咱们的调用方式就可以这样写了:
很明显,这个test2肯定是一个静态方法了,再来反编译看一下:
bogon:kotlin_lecture xiongwei$ javap -verbose com/kotlin/test11/MyClass2.class Classfile /Users/xiongwei/Documents/workspace/IntelliJSpace/kotlin_lecture/out/production/kotlin_lecture/com/kotlin/test11/MyClass2.class Last modified 2019-9-21; size 858 bytes MD5 checksum 7b8819a8b4e7417db633e619b794273f Compiled from "HelloKotlin7.kt" public final class com.kotlin.test11.MyClass2 minor version: 0 major version: 52 flags: ACC_PUBLIC, ACC_FINAL, ACC_SUPER Constant pool: #1 = Utf8 com/kotlin/test11/MyClass2 #2 = Class #1 // com/kotlin/test11/MyClass2 #3 = Utf8 java/lang/Object #4 = Class #3 // java/lang/Object #5 = Utf8 <init> #6 = Utf8 ()V #7 = NameAndType #5:#6 // "<init>":()V #8 = Methodref #4.#7 // java/lang/Object."<init>":()V #9 = Utf8 this #10 = Utf8 Lcom/kotlin/test11/MyClass2; #11 = Utf8 <clinit> #12 = Utf8 Companion #13 = Utf8 Lcom/kotlin/test11/MyClass2$Companion; #14 = Utf8 Lkotlin/Metadata; #15 = Utf8 mv #16 = Integer 1 #17 = Integer 15 #18 = Utf8 bv #19 = Integer 0 #20 = Integer 3 #21 = Utf8 k #22 = Utf8 d1 #23 = Utf8 \n\n\ 20:B¢¨ #24 = Utf8 d2 #25 = Utf8 #26 = Utf8 kotlin_lecture #27 = Utf8 test2 #28 = Utf8 Lkotlin/jvm/JvmStatic; #29 = NameAndType #12:#13 // Companion:Lcom/kotlin/test11/MyClass2$Companion; #30 = Fieldref #2.#29 // com/kotlin/test11/MyClass2.Companion:Lcom/kotlin/test11/MyClass2$Companion; #31 = Utf8 com/kotlin/test11/MyClass2$Companion #32 = Class #31 // com/kotlin/test11/MyClass2$Companion #33 = NameAndType #27:#6 // test2:()V #34 = Methodref #32.#33 // com/kotlin/test11/MyClass2$Companion.test2:()V #35 = Utf8 (Lkotlin/jvm/internal/DefaultConstructorMarker;)V #36 = NameAndType #5:#35 // "<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V #37 = Methodref #32.#36 // com/kotlin/test11/MyClass2$Companion."<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V #38 = Utf8 HelloKotlin7.kt #39 = Utf8 Code #40 = Utf8 LineNumberTable #41 = Utf8 LocalVariableTable #42 = Utf8 RuntimeVisibleAnnotations #43 = Utf8 InnerClasses #44 = Utf8 SourceFile { public static final com.kotlin.test11.MyClass2$Companion Companion; descriptor: Lcom/kotlin/test11/MyClass2$Companion; flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL public com.kotlin.test11.MyClass2(); descriptor: ()V flags: ACC_PUBLIC Code: stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>":()V 4: return LineNumberTable: line 3: 0 LocalVariableTable: Start Length Slot Name Signature 0 5 0 this Lcom/kotlin/test11/MyClass2; static {}; descriptor: ()V flags: ACC_STATIC Code: stack=3, locals=0, args_size=0 0: new #32 // class com/kotlin/test11/MyClass2$Companion 3: dup 4: aconst_null 5: invokespecial #37 // Method com/kotlin/test11/MyClass2$Companion."<init>":(Lkotlin/jvm/internal/DefaultConstructorMarker;)V 8: putstatic #30 // Field Companion:Lcom/kotlin/test11/MyClass2$Companion; 11: return public static final void test2(); descriptor: ()V flags: ACC_PUBLIC, ACC_STATIC, ACC_FINAL Code: stack=1, locals=0, args_size=0 0: getstatic #30 // Field Companion:Lcom/kotlin/test11/MyClass2$Companion; 3: invokevirtual #34 // Method com/kotlin/test11/MyClass2$Companion.test2:()V 6: return RuntimeVisibleAnnotations: 0: #28() } InnerClasses: public static final #12= #32 of #2; //Companion=class com/kotlin/test11/MyClass2$Companion of class com/kotlin/test11/MyClass2 SourceFile: "HelloKotlin7.kt" RuntimeVisibleAnnotations: 0: #14(#15=[I#16,I#16,I#17],#18=[I#16,I#19,I#20],#21=I#16,#22=[s#23],#24=[s#10,s#25,s#6,s#12,s#26])
此时确实在MyClass2字节码中生成了一个静态的test2()方法了,而它的实现很明显可以看到,它最终是调用了Companion.test2(),其根本就是由该@JvmStatic注解发生了作用。