java - 为什么内部类构造函数中的外部类对象的 LocalVariableTable 中没有条目(Java 字节码)

Question

第1步:我编译了以下代码:

public class OuterClass {
class InnerClass{

    }
}  

我有 OuterClass.class 和 OterClass$InnerClass.class

Step2:我使用javap来检查内部类的字节码。很奇怪的是构造函数方法使用了“1:aload_1”，但是在LocalVariableTable中，只有一个“this”的条目可以被aload_0访问。我假设aload_1是将传入的参数——外部类对象的引用——加载到栈顶。

我的问题:为什么编译器不为其创建一个条目(传递给构造函数的外部类的引用)？

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;


}

Answer 1

LocalVariableTable 纯粹用于调试目的 - 它对执行没有影响。因此，它只包含源可见变量，因为这是调试器感兴趣的内容。没有理由包含编译器生成的变量。