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[英]Java - object of a private inner class being as an argument to an outer class' constructor
[英]Why isn't there an entry in LocalVariableTable for outer class object in an inner class constructor(Java Bytecode)
第一步:我编译了以下代码:
public class OuterClass {
class InnerClass{
}
}
我有 OuterClass.class 和 OterClass$InnerClass.class
Step2:我用javap查看了内部class的字节码,很奇怪构造方法使用的是“1:aload_1”,但是在LocalVariableTable中,只有aload_0可以访问到的“this”表项。 我假设 aload_1 是将传入参数——即外部 class 对象的引用——加载到堆栈的顶部。
我的问题:为什么编译器不为它创建一个条目(传递给构造函数的外部 class 的引用)?
我尝试使用 Jsdk 1.4 和 openjdk 1.6。
~$ javap -v -c OuterClass\$InnerClass
Compiled from "OuterClass.java"
class OuterClass$InnerClass extends java.lang.Object
SourceFile: "OuterClass.java"
InnerClass:
#24= #1 of #22; //InnerClass=class OuterClass$InnerClass of class OuterClass
minor version: 0
major version: 50
Constant pool:
const #1 = class #2; // OuterClass$InnerClass
const #2 = Asciz OuterClass$InnerClass;
const #3 = class #4; // java/lang/Object
const #4 = Asciz java/lang/Object;
const #5 = Asciz this$0;
const #6 = Asciz LOuterClass;;
const #7 = Asciz <init>;
const #8 = Asciz (LOuterClass;)V;
const #9 = Asciz Code;
const #10 = Field #1.#11; // OuterClass$InnerClass.this$0:LOuterClass;
const #11 = NameAndType #5:#6;// this$0:LOuterClass;
const #12 = Method #3.#13; // java/lang/Object."<init>":()V
const #13 = NameAndType #7:#14;// "<init>":()V
const #14 = Asciz ()V;
const #15 = Asciz LineNumberTable;
const #16 = Asciz LocalVariableTable;
const #17 = Asciz this;
const #18 = Asciz LOuterClass$InnerClass;;
const #19 = Asciz SourceFile;
const #20 = Asciz OuterClass.java;
const #21 = Asciz InnerClasses;
const #22 = class #23; // OuterClass
const #23 = Asciz OuterClass;
const #24 = Asciz InnerClass;
{
final OuterClass this$0;
OuterClass$InnerClass(OuterClass);
Code:
Stack=2, Locals=2, Args_size=2
0: aload_0
1: aload_1
2: putfield #10; //Field this$0:LOuterClass;
5: aload_0
6: invokespecial #12; //Method java/lang/Object."<init>":()V
9: return
LineNumberTable:
line 3: 0
LocalVariableTable:
Start Length Slot Name Signature
0 10 0 this LOuterClass$InnerClass;
}
LocalVariableTable
纯粹用于调试目的 - 它对执行没有影响。 因此,它只包括源可见变量,因为这是调试器感兴趣的。没有理由包括编译器生成的变量。
我认为这只是因为它不需要局部变量表中的条目,是一个不需要以任何其他方式引用的参数,而不是作为参数。
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