內部類之所以可以訪問外部類的成員變量，是因爲內部類中引用了外部類的成員變量
參考:http://blog.csdn.net/blumamy/article/details/43303963
參考上面的文章之後，匿名內部類之所以可以引用局部變量，自然是因爲持有局部變量的引用，也是通過類似於構造函數的方式將此變量傳遞到內部類裏面，在內部類裏面會重新有一個變量來引用局部變量所引用的對象，如果局部變量沒有用final修飾，那麼當改變的時候，內部類所引用的變量不會因爲他的改變而改變，所以局部變量必須用final修飾。
測試如下:
public class JavaDemo {
private String name;
private int num;
void testInner(){
final String picture="戴爾";
new Inner(){
public void showName(){
System.out.println(picture);
}
};
}
class Inner{
}
}
在內部類Inner中會有一個變量持有傳遞過來的final修飾的picture變量，類似於
String innerPicture = picture;
在JavaDemo$1字節碼中是如下格式
Last modified 2015-12-14; size 569 bytes
MD5 checksum d52c1f747d7b708cb19cd659e3d5d9ac
Compiled from "JavaDemo.java"
class JavaDemo$1 extends JavaDemo$Inner
SourceFile: "JavaDemo.java"
EnclosingMethod: #19.#20 // JavaDemo.testInner
InnerClasses:
#6; //class JavaDemo$1
#32= #7 of #19; //Inner=class JavaDemo$Inner of class JavaDemo
minor version: 0
major version: 51
flags: ACC_SUPER
Constant pool:
#1 = Fieldref #6.#21 // JavaDemo$1.this$0:LJavaDemo;
#2 = Methodref #7.#22 // JavaDemo$Inner."<init>":(LJavaDemo;)V
#3 = Fieldref #23.#24 // java/lang/System.out:Ljava/io/PrintStream;
#4 = String #25 // 戴爾
#5 = Methodref #26.#27 // java/io/PrintStream.println:(Ljava/lang/String;)V
#6 = Class #28 // JavaDemo$1
#7 = Class #31 // JavaDemo$Inner
#8 = Utf8 this$0
#9 = Utf8 LJavaDemo;
#10 = Utf8 <init>
#11 = Utf8 (LJavaDemo;)V
#12 = Utf8 Code
#13 = Utf8 LineNumberTable
#14 = Utf8 showName
#15 = Utf8 ()V
#16 = Utf8 SourceFile
#17 = Utf8 JavaDemo.java
#18 = Utf8 EnclosingMethod
#19 = Class #33 // JavaDemo
#20 = NameAndType #34:#15 // testInner:()V
#21 = NameAndType #8:#9 // this$0:LJavaDemo;
#22 = NameAndType #10:#11 // "<init>":(LJavaDemo;)V
#23 = Class #35 // java/lang/System
#24 = NameAndType #36:#37 // out:Ljava/io/PrintStream;
#25 = Utf8 戴爾
#26 = Class #38 // java/io/PrintStream
#27 = NameAndType #39:#40 // println:(Ljava/lang/String;)V
#28 = Utf8 JavaDemo$1
#29 = Utf8
#30 = Utf8 InnerClasses
#31 = Utf8 JavaDemo$Inner
#32 = Utf8 Inner
#33 = Utf8 JavaDemo
#34 = Utf8 testInner
#35 = Utf8 java/lang/System
#36 = Utf8 out
#37 = Utf8 Ljava/io/PrintStream;
#38 = Utf8 java/io/PrintStream
#39 = Utf8 println
#40 = Utf8 (Ljava/lang/String;)V
{
final JavaDemo this$0;
flags: ACC_FINAL, ACC_SYNTHETIC
JavaDemo$1(JavaDemo);
flags:
Code:
stack=2, locals=2, args_size=2
0: aload_0
1: aload_1
2: putfield #1 // Field this$0:LJavaDemo;
5: aload_0
6: aload_1
7: invokespecial #2 // Method JavaDemo$Inner."<init>":(LJavaDemo;)V
10: return
LineNumberTable:
line 12: 0
public void showName();
flags: ACC_PUBLIC
Code:
stack=2, locals=1, args_size=1
0: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #4 // String 戴爾
5: invokevirtual #5 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: return
LineNumberTable:
line 14: 0
line 15: 8
}
其他:
當內部類引用成員變量的時候，是將外部類生成的對象傳遞進入內部類，而這個對象相對於內部類對象是唯一不變的，他們是共存的，有內部類對象的時候，外部類對象是必然存在的，而且是唯一的，所以內部類都有一個外部類對象的引用，當外部類的變量發生變化，內部類在調用外部類變量的時候，會先尋找外部類對象地址，再調用該對象的變量。
如上面的 final JavaDemo this$0;
附上JavaDemo.class 和JavaDemo$Inner.class
Classfile /C:/Users/lizheng-ds3/Desktop/test/JavaDemo.class
Last modified 2015-12-14; size 424 bytes
MD5 checksum e046fc0b074cc03c114a7052e5c2328b
Compiled from "JavaDemo.java"
public class JavaDemo
SourceFile: "JavaDemo.java"
InnerClasses:
#7= #6 of #4; //Inner=class JavaDemo$Inner of class JavaDemo
#2; //class JavaDemo$1
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #5.#21 // java/lang/Object."<init>":()V
#2 = Class #22 // JavaDemo$1
#3 = Methodref #2.#23 // JavaDemo$1."<init>":(LJavaDemo;)V
#4 = Class #24 // JavaDemo
#5 = Class #25 // java/lang/Object
#6 = Class #26 // JavaDemo$Inner
#7 = Utf8 Inner
#8 = Utf8 InnerClasses
#9 = Utf8
#10 = Utf8 name
#11 = Utf8 Ljava/lang/String;
#12 = Utf8 num
#13 = Utf8 I
#14 = Utf8 <init>
#15 = Utf8 ()V
#16 = Utf8 Code
#17 = Utf8 LineNumberTable
#18 = Utf8 testInner
#19 = Utf8 SourceFile
#20 = Utf8 JavaDemo.java
#21 = NameAndType #14:#15 // "<init>":()V
#22 = Utf8 JavaDemo$1
#23 = NameAndType #14:#27 // "<init>":(LJavaDemo;)V
#24 = Utf8 JavaDemo
#25 = Utf8 java/lang/Object
#26 = Utf8 JavaDemo$Inner
#27 = Utf8 (LJavaDemo;)V
{
public JavaDemo();
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 4: 0
line 19: 4
void testInner();
flags:
Code:
stack=3, locals=2, args_size=1
0: new #2 // class JavaDemo$1
3: dup
4: aload_0
5: invokespecial #3 // Method JavaDemo$1."<init>":(LJavaDemo;)V
8: pop
9: return
LineNumberTable:
line 12: 0
line 17: 9
}
------------------------
Classfile /C:/Users/lizheng-ds3/Desktop/test/JavaDemo$Inner.class
Last modified 2015-12-14; size 310 bytes
MD5 checksum f4de5d1e3475cd1ae4efd3e4a111e068
Compiled from "JavaDemo.java"
class JavaDemo$Inner
SourceFile: "JavaDemo.java"
InnerClasses:
#17= #3 of #15; //Inner=class JavaDemo$Inner of class JavaDemo
minor version: 0
major version: 51
flags: ACC_SUPER
Constant pool:
#1 = Fieldref #3.#13 // JavaDemo$Inner.this$0:LJavaDemo;
#2 = Methodref #4.#14 // java/lang/Object."<init>":()V
#3 = Class #16 // JavaDemo$Inner
#4 = Class #19 // java/lang/Object
#5 = Utf8 this$0
#6 = Utf8 LJavaDemo;
#7 = Utf8 <init>
#8 = Utf8 (LJavaDemo;)V
#9 = Utf8 Code
#10 = Utf8 LineNumberTable
#11 = Utf8 SourceFile
#12 = Utf8 JavaDemo.java
#13 = NameAndType #5:#6 // this$0:LJavaDemo;
#14 = NameAndType #7:#20 // "<init>":()V
#15 = Class #21 // JavaDemo
#16 = Utf8 JavaDemo$Inner
#17 = Utf8 Inner
#18 = Utf8 InnerClasses
#19 = Utf8 java/lang/Object
#20 = Utf8 ()V
#21 = Utf8 JavaDemo
{
final JavaDemo this$0;
flags: ACC_FINAL, ACC_SYNTHETIC
JavaDemo$Inner(JavaDemo);
flags:
Code:
stack=2, locals=2, args_size=2
0: aload_0
1: aload_1
2: putfield #1 // Field this$0:LJavaDemo;
5: aload_0
6: invokespecial #2 // Method java/lang/Object."<init>":()V
9: return
LineNumberTable:
line 19: 0
}
查看class文件方式
javac -verbose class文件目錄