一、前言
对于内部类平时编码时使用的场景不多，比较常用的地方应该就是绑定事件处理程序的时候了（从C#、JS转向Java阵营的孩子总不不习惯用匿名内部类来做事件订阅:(）。本文将结合Bytecode对四种内部类作介绍，当作一次梳理以便日后查阅。
首先要明确的是内部类是编译器提供的特性，编译器会将含内部类的java文件编译成外部类和内部类的N个文件（N>=2） ，然后JVM就按普通类的方式运行。就如下面的源码会被编译为Outer.class和和Outer$Inner.class文件。
class Outer{
class Inner{}
}
三、成员内部类
定义在一个类的内部。相对外部类仅有默认和public两种访问修饰符而言，成员内部类可有默认、private、proteced和public四种访问修饰符，效果与成员字段和方法的一样。
示例：
import java.io.*;
// Main.java文件
class Main{
public static void main(String[] args) throws IOException{
MemberCls outer = new MemberCls();
Inner inner1 = outer.new Inner();
Inner inner2 = outer.getInner(); System.out.println(inner1.getVal());
System.out.println(inner2.getVal());
inner1.setVal();
System.out.println(inner1.getVal());
System.out.println(inner2.getVal());
inner2.setVal();
System.out.println(inner1.getVal());
System.out.println(inner2.getVal()); System.in.read();
}
}
// MemberCls.java文件
class MemberCls{
private int val = ; class Inner{
void setVal(int val){
MemberCls.this.val = val;
}
int getVal(){
return val;
}
} Inner getInner(){
return new Inner();
}
// 运行结果
// 1
// 1
// 2
// 2
// 3
//
并生成MemberCls.class和MemberCls$Inner.class两个类文件。
Classfile /F:/skyDrive/repos/self/jottings/java/sample//MemberCls.class
Last modified --; size bytes
MD5 checksum aea71084f78ab319a339717e4d0e1e79
Compiled from "MemberCls.java"
class MemberCls
SourceFile: "MemberCls.java"
InnerClasses:
#= # of #; //Inner=class MemberCls$Inner of class MemberCls
minor version:
major version:
flags: ACC_SUPERConstant pool:
# = Fieldref #.# // MemberCls.val:I
# = Methodref #.# // java/lang/Object."<init>":()V
# = Class # // MemberCls$Inner
# = Methodref #.# // MemberCls$Inner."<init>":(LMemberCls;)V
# = Class # // MemberCls
# = Methodref #.# // MemberCls."<init>":()V
# = Methodref #.# // java/lang/Object.getClass:()Ljava/lang/Class;
# = Methodref #.# // MemberCls.getInner:()LMemberCls$Inner;
# = Fieldref #.# // java/lang/System.out:Ljava/io/PrintStream;
# = Methodref #.# // MemberCls$Inner.getVal:()I
# = Methodref #.# // java/io/PrintStream.println:(I)V
# = Methodref #.# // MemberCls$Inner.setVal:(I)V
# = Fieldref #.# // java/lang/System.in:Ljava/io/InputStream;
# = Methodref #.# // java/io/InputStream.read:()I
# = Class # // java/lang/Object
# = Utf8 Inner
# = Utf8 InnerClasses
# = Utf8 val
# = Utf8 I
# = Utf8 <init>
# = Utf8 ()V
# = Utf8 Code
# = Utf8 LineNumberTable
# = Utf8 getInner
# = Utf8 ()LMemberCls$Inner;
# = Utf8 main
# = Utf8 ([Ljava/lang/String;)V
# = Utf8 Exceptions
# = Class # // java/io/IOException
# = Utf8 access$
# = Utf8 (LMemberCls;I)I
# = Utf8 access$
# = Utf8 (LMemberCls;)I
# = Utf8 SourceFile
# = Utf8 MemberCls.java
# = NameAndType #:# // val:I
# = NameAndType #:# // "<init>":()V
# = Utf8 MemberCls$Inner
# = NameAndType #:# // "<init>":(LMemberCls;)V
# = Utf8 MemberCls
# = NameAndType #:# // getClass:()Ljava/lang/Class;
# = NameAndType #:# // getInner:()LMemberCls$Inner;
# = Class # // java/lang/System
# = NameAndType #:# // out:Ljava/io/PrintStream;
# = NameAndType #:# // getVal:()I
# = Class # // java/io/PrintStream
# = NameAndType #:# // println:(I)V
# = NameAndType #:# // setVal:(I)V
# = NameAndType #:# // in:Ljava/io/InputStream;
# = Class # // java/io/InputStream
# = NameAndType #:# // read:()I
# = Utf8 java/lang/Object
# = Utf8 java/io/IOException
# = Utf8 (LMemberCls;)V
# = Utf8 getClass
# = Utf8 ()Ljava/lang/Class;
# = Utf8 java/lang/System
# = Utf8 out
# = Utf8 Ljava/io/PrintStream;
# = Utf8 getVal
# = Utf8 ()I
# = Utf8 java/io/PrintStream
# = Utf8 println
# = Utf8 (I)V
# = Utf8 setVal
# = Utf8 in
# = Utf8 Ljava/io/InputStream;
# = Utf8 java/io/InputStream
# = Utf8 read
{
MemberCls();
flags: Code:
stack=, locals=, args_size=
: aload_0
: invokespecial # // Method java/lang/Object."<init>":()V
: aload_0
: iconst_1
: putfield # // Field val:I
: return
LineNumberTable:
line :
line :
line : MemberCls$Inner getInner();
flags: Code:
stack=, locals=, args_size=
: new # // class MemberCls$Inner
: dup
: aload_0
: invokespecial # // Method MemberCls$Inner."<init>":(LMemberCls;)V
: areturn
LineNumberTable:
line : public static void main(java.lang.String[]) throws java.io.IOException;
flags: ACC_PUBLIC, ACC_STATIC Code:
stack=, locals=, args_size=
: new # // class MemberCls
: dup
: invokespecial # // Method "<init>":()V
: astore_1
: new # // class MemberCls$Inner
: dup
: aload_1
: dup
: invokevirtual # // Method java/lang/Object.getClass:()Ljava/lang/Class;
: pop
: invokespecial # // Method MemberCls$Inner."<init>":(LMemberCls;)V
: astore_2
: aload_1
: invokevirtual # // Method getInner:()LMemberCls$Inner;
: astore_3
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_3
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: aload_2
: iconst_2
: invokevirtual # // Method MemberCls$Inner.setVal:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_3
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: aload_3
: iconst_3
: invokevirtual # // Method MemberCls$Inner.setVal:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_3
: invokevirtual # // Method MemberCls$Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: getstatic # // Field java/lang/System.in:Ljava/io/InputStream;
: invokevirtual # // Method java/io/InputStream.read:()I
: pop
: return
LineNumberTable:
line :
line :
line :
line :
line :
line :
line :
line :
line :
line :
line :
line :
line :
Exceptions:
throws java.io.IOException static int access$(MemberCls, int);
flags: ACC_STATIC, ACC_SYNTHETIC Code:
stack=, locals=, args_size=
: aload_0
: iload_1
: dup_x1
: putfield # // Field val:I
: ireturn
LineNumberTable:
line : static int access$(MemberCls);
flags: ACC_STATIC, ACC_SYNTHETIC Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field val:I
: ireturn
LineNumberTable:
line :
}
MemberCls.class
Classfile /F:/skyDrive/repos/self/jottings/java/sample//MemberCls$Inner.class
Last modified --; size bytes
MD5 checksum b092ffe3c5b358c786d99d98c104dc40
Compiled from "MemberCls.java"
class MemberCls$Inner
SourceFile: "MemberCls.java"
InnerClasses:
#= # of #; //Inner=class MemberCls$Inner of class MemberCls
minor version:
major version:
flags: ACC_SUPERConstant pool:
# = Fieldref #.# // MemberCls$Inner.this$0:LMemberCls;
# = Methodref #.# // java/lang/Object."<init>":()V
# = Methodref #.# // MemberCls.access$002:(LMemberCls;I)I
# = Methodref #.# // MemberCls.access$000:(LMemberCls;)I
# = Class # // MemberCls$Inner
# = Class # // java/lang/Object
# = Utf8 this$
# = Utf8 LMemberCls;
# = Utf8 <init>
# = Utf8 (LMemberCls;)V
# = Utf8 Code
# = Utf8 LineNumberTable
# = Utf8 setVal
# = Utf8 (I)V
# = Utf8 getVal
# = Utf8 ()I
# = Utf8 SourceFile
# = Utf8 MemberCls.java
# = NameAndType #:# // this$0:LMemberCls;
# = NameAndType #:# // "<init>":()V
# = Class # // MemberCls
# = NameAndType #:# // access$002:(LMemberCls;I)I
# = NameAndType #:# // access$000:(LMemberCls;)I
# = Utf8 MemberCls$Inner
# = Utf8 Inner
# = Utf8 InnerClasses
# = Utf8 java/lang/Object
# = Utf8 ()V
# = Utf8 MemberCls
# = Utf8 access$
# = Utf8 (LMemberCls;I)I
# = Utf8 access$
# = Utf8 (LMemberCls;)I
{
final MemberCls this$;
flags: ACC_FINAL, ACC_SYNTHETIC MemberCls$Inner(MemberCls);
flags: Code:
stack=, locals=, args_size=
: aload_0
: aload_1
: putfield # // Field this$0:LMemberCls;
: aload_0
: invokespecial # // Method java/lang/Object."<init>":()V
: return
LineNumberTable:
line : void setVal(int);
flags: Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LMemberCls;
: iload_1
: invokestatic # // Method MemberCls.access$002:(LMemberCls;I)I
: pop
: return
LineNumberTable:
line :
line : int getVal();
flags: Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LMemberCls;
: invokestatic # // Method MemberCls.access$000:(LMemberCls;)I
: ireturn
LineNumberTable:
line :
}
MemberCls$Inner.class
由于成员内部类依赖于外部类实例，因此创建内部类实例时要先创建外部类实例，然后通过下列两种形式来创建内部类实例：
// 方式一
内部类 内部类实例 = 外部类实例.new 内部类();// 方式二
外部类{
内部类{}
内部类 get内部类(){
return new 内部类();
}
}
内部类 内部类实例 = 外部类实例.get内部类();
注意：
1. 当成员内部类拥有与外部类同名的成员变量或方法时，默认是使用成员内部类的成员。若要访问外部类的同名成员，则需要进行如下操作：
外部类.this.成员变量;
外部类.this.成员方法;
2. 对于同一个外部类实例创建的内部类实例，这些内部类实例均操作同一个外部实例。像上述例子那样，均操作同一个val字段。
看Bytecodes可知，编译器自动为MemberCls创建创建两个静态方法access$002和access$000，而MemberCls$Inner实例则通过这两个静态方法访问私有私有字段val的。
// MemberCls.class文件/** 等价于
* static int setVal(MemberCls outer, int val){
* outer.val = val;
* return val;
* }
*/
static int access$(MemberCls, int);
flags: ACC_STATIC, ACC_SYNTHETIC
Code:
stack=, locals=, args_size=
: aload_0
: iload_1
: dup_x1
: putfield # // Field val:I
: ireturn
LineNumberTable:
line : /** 等价于
* static int getVal(MemberCls outer){
* return outer.val;
* }
*/
static int access$(MemberCls);
flags: ACC_STATIC, ACC_SYNTHETIC
Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field val:I
: ireturn
LineNumberTable:
line :
// MemberCls$Inner.class文件/** 等价于
* void setVal(int val){
* MemberCls实例.setVal(val);
* }
*/
void setVal(int);
flags:
Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LMemberCls;
: iload_1
: invokestatic # // Method MemberCls.access$002:(LMemberCls;I)I
: pop
: return
LineNumberTable:
line :
line : /** 等价于
* int getVal(int val){
* MemberCls实例.getVal();
* }
*/
int getVal();
flags:
Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LMemberCls;
: invokestatic # // Method MemberCls.access$000:(LMemberCls;)I
: ireturn
LineNumberTable:
line :
因此内部类可以访问外部类的所有类型的字段和方法（包括private）。
四、局部内部类
局部内部类定义在方法或某个作用域里面，并且仅限于方法和该作用域内访问。
示例：
import java.io.*;class Main{
public static void main(String[] args) throws IOException{
LocalCls outer = new LocalCls();
outer.print(); System.in.read();
}
}class LocalCls{
private int val = ; void print(){
final String name = "fsjohnhuang";
class Inner{
int getVal(){
return val;
}
void setVal(int val){
LocalCls.this.val = val;
}
String getName(){
return name;
}
} Inner inner = new Inner();
System.out.println(inner.getVal());
inner.setVal();
System.out.println(inner.getVal());
System.out.println(inner.getName());
}
}
// 结果：
// 1
// 2
// fsjohnhuang
生成LocalCls.class和LocalCls$1Inner.class两个类文件。
Classfile /F:/skyDrive/repos/self/jottings/java/sample//LocalCls.class
Last modified --; size bytes
MD5 checksum a636f470da37d8c1cb9370dde083d6d8
Compiled from "LocalCls.java"
class LocalCls
SourceFile: "LocalCls.java"
InnerClasses:
#= #; //Inner=class LocalCls$1Inner
minor version:
major version:
flags: ACC_SUPERConstant pool:
# = Fieldref #.# // LocalCls.val:I
# = Methodref #.# // java/lang/Object."<init>":()V
# = Class # // LocalCls
# = Methodref #.# // LocalCls."<init>":()V
# = Methodref #.# // LocalCls.print:()V
# = Fieldref #.# // java/lang/System.in:Ljava/io/InputStream;
# = Methodref #.# // java/io/InputStream.read:()I
# = Class # // LocalCls$1Inner
# = Methodref #.# // LocalCls$1Inner."<init>":(LLocalCls;)V
# = Fieldref #.# // java/lang/System.out:Ljava/io/PrintStream;
# = Methodref #.# // LocalCls$1Inner.getVal:()I
# = Methodref #.# // java/io/PrintStream.println:(I)V
# = Methodref #.# // LocalCls$1Inner.setVal:(I)V
# = Methodref #.# // LocalCls$1Inner.getName:()Ljava/lang/String;
# = Methodref #.# // java/io/PrintStream.println:(Ljava/lang/String;)V
# = Class # // java/lang/Object
# = Utf8 Inner
# = Utf8 InnerClasses
# = Utf8 val
# = Utf8 I
# = Utf8 <init>
# = Utf8 ()V
# = Utf8 Code
# = Utf8 LineNumberTable
# = Utf8 main
# = Utf8 ([Ljava/lang/String;)V
# = Utf8 Exceptions
# = Class # // java/io/IOException
# = Utf8 print
# = Utf8 access$
# = Utf8 (LLocalCls;)I
# = Utf8 access$
# = Utf8 (LLocalCls;I)I
# = Utf8 SourceFile
# = Utf8 LocalCls.java
# = NameAndType #:# // val:I
# = NameAndType #:# // "<init>":()V
# = Utf8 LocalCls
# = NameAndType #:# // print:()V
# = Class # // java/lang/System
# = NameAndType #:# // in:Ljava/io/InputStream;
# = Class # // java/io/InputStream
# = NameAndType #:# // read:()I
# = Utf8 LocalCls$1Inner
# = NameAndType #:# // "<init>":(LLocalCls;)V
# = NameAndType #:# // out:Ljava/io/PrintStream;
# = NameAndType #:# // getVal:()I
# = Class # // java/io/PrintStream
# = NameAndType #:# // println:(I)V
# = NameAndType #:# // setVal:(I)V
# = NameAndType #:# // getName:()Ljava/lang/String;
# = NameAndType #:# // println:(Ljava/lang/String;)V
# = Utf8 java/lang/Object
# = Utf8 java/io/IOException
# = Utf8 java/lang/System
# = Utf8 in
# = Utf8 Ljava/io/InputStream;
# = Utf8 java/io/InputStream
# = Utf8 read
# = Utf8 ()I
# = Utf8 (LLocalCls;)V
# = Utf8 out
# = Utf8 Ljava/io/PrintStream;
# = Utf8 getVal
# = Utf8 java/io/PrintStream
# = Utf8 println
# = Utf8 (I)V
# = Utf8 setVal
# = Utf8 getName
# = Utf8 ()Ljava/lang/String;
# = Utf8 (Ljava/lang/String;)V
{
LocalCls();
flags: Code:
stack=, locals=, args_size=
: aload_0
: invokespecial # // Method java/lang/Object."<init>":()V
: aload_0
: iconst_1
: putfield # // Field val:I
: return
LineNumberTable:
line :
line : public static void main(java.lang.String[]) throws java.io.IOException;
flags: ACC_PUBLIC, ACC_STATIC Code:
stack=, locals=, args_size=
: new # // class LocalCls
: dup
: invokespecial # // Method "<init>":()V
: astore_1
: aload_1
: invokevirtual # // Method print:()V
: getstatic # // Field java/lang/System.in:Ljava/io/InputStream;
: invokevirtual # // Method java/io/InputStream.read:()I
: pop
: return
LineNumberTable:
line :
line :
line :
line :
Exceptions:
throws java.io.IOException void print();
flags: Code:
stack=, locals=, args_size=
: new # // class LocalCls$1Inner
: dup
: aload_0
: invokespecial # // Method LocalCls$1Inner."<init>":(LLocalCls;)V
: astore_2
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method LocalCls$1Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: aload_2
: iconst_2
: invokevirtual # // Method LocalCls$1Inner.setVal:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method LocalCls$1Inner.getVal:()I
: invokevirtual # // Method java/io/PrintStream.println:(I)V
: getstatic # // Field java/lang/System.out:Ljava/io/PrintStream;
: aload_2
: invokevirtual # // Method LocalCls$1Inner.getName:()Ljava/lang/String;
: invokevirtual # // Method java/io/PrintStream.println:(Ljava/lang/String;)V
: return
LineNumberTable:
line :
line :
line :
line :
line :
line : static int access$(LocalCls);
flags: ACC_STATIC, ACC_SYNTHETIC Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field val:I
: ireturn
LineNumberTable:
line : static int access$(LocalCls, int);
flags: ACC_STATIC, ACC_SYNTHETIC Code:
stack=, locals=, args_size=
: aload_0
: iload_1
: dup_x1
: putfield # // Field val:I
: ireturn
LineNumberTable:
line :
}
LocalCls.class
Classfile /F:/skyDrive/repos/self/jottings/java/sample//LocalCls$1Inner.class
Last modified --; size bytes
MD5 checksum a4bf7c12f15f22b2ebb3f79438a555ab
Compiled from "LocalCls.java"
class LocalCls$1Inner
SourceFile: "LocalCls.java"
EnclosingMethod: #.# // LocalCls.print
InnerClasses:
#= #; //Inner=class LocalCls$1Inner
minor version:
major version:
flags: ACC_SUPERConstant pool:
# = Fieldref #.# // LocalCls$1Inner.this$0:LLocalCls;
# = Methodref #.# // java/lang/Object."<init>":()V
# = Methodref #.# // LocalCls.access$000:(LLocalCls;)I
# = Methodref #.# // LocalCls.access$002:(LLocalCls;I)I
# = String # // fsjohnhuang
# = Class # // LocalCls$1Inner
# = Class # // java/lang/Object
# = Utf8 this$
# = Utf8 LLocalCls;
# = Utf8 <init>
# = Utf8 (LLocalCls;)V
# = Utf8 Code
# = Utf8 LineNumberTable
# = Utf8 getVal
# = Utf8 ()I
# = Utf8 setVal
# = Utf8 (I)V
# = Utf8 getName
# = Utf8 ()Ljava/lang/String;
# = Utf8 SourceFile
# = Utf8 LocalCls.java
# = Utf8 EnclosingMethod
# = Class # // LocalCls
# = NameAndType #:# // print:()V
# = NameAndType #:# // this$0:LLocalCls;
# = NameAndType #:# // "<init>":()V
# = NameAndType #:# // access$000:(LLocalCls;)I
# = NameAndType #:# // access$002:(LLocalCls;I)I
# = Utf8 fsjohnhuang
# = Utf8 LocalCls$1Inner
# = Utf8 Inner
# = Utf8 InnerClasses
# = Utf8 java/lang/Object
# = Utf8 LocalCls
# = Utf8 print
# = Utf8 ()V
# = Utf8 access$
# = Utf8 (LLocalCls;)I
# = Utf8 access$
# = Utf8 (LLocalCls;I)I
{
final LocalCls this$;
flags: ACC_FINAL, ACC_SYNTHETIC LocalCls$1Inner(LocalCls);
flags: Code:
stack=, locals=, args_size=
: aload_0
: aload_1
: putfield # // Field this$0:LLocalCls;
: aload_0
: invokespecial # // Method java/lang/Object."<init>":()V
: return
LineNumberTable:
line : int getVal();
flags: Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LLocalCls;
: invokestatic # // Method LocalCls.access$000:(LLocalCls;)I
: ireturn
LineNumberTable:
line : void setVal(int);
flags: Code:
stack=, locals=, args_size=
: aload_0
: getfield # // Field this$0:LLocalCls;
: iload_1
: invokestatic # // Method LocalCls.access$002:(LLocalCls;I)I
: pop
: return
LineNumberTable:
line :
line : java.lang.String getName();
flags: Code:
stack=, locals=, args_size=
: ldc # // String fsjohnhuang
: areturn
LineNumberTable:
line :
}
LocalCls$1Inner.class
上述两个类文件与成员内部类的几乎一模一样，那么就是说内部类作用范围的限制其实是编译器的限制，而不是JVM的限制了。
注意：
1. 不能有public、protected、private和static作修饰；
2. 局部内部类中仅能访问方法或作用域内的常量，若访问的是变量则编译时会出错。
Q：为什么不能访问局部变量呢？
A：假设可以访问局部变量，那么要考虑的是如何引用到局部变量。
首先局部变量是存放在JVM栈帧中的局部变量表中，并且当方法执行完栈帧也随之弹出，也就是说局部变量所占的内存空间是短暂的（不稳定）。
假如局部变量A是基本类型的话，那么数据直接就存放在局部变量表中相应的Slots中，方法执行完就没了。那局部内部类中所访问的局部变量A到底是什么就无从得知了！ 假如局部变量A是String类型或其他类类型，那么局部内部类中访问的局部变量A时就有两种方式了，第一种是访问String常量池中该字符串的地址，第二种是指向局部变量A的地址，然后通过变量A去访问String常量池中该字符串。
但上述这些均是在运行时才能决定，而编译时是无法正确地被描述出来。并且由于内部类将被编译成独立的类文件，访问其他类方法的局部变量的操作无法在类文件中描述。而常量则可以在内部类文件的常量池部分中被正确地描述，而JVM中处理时也十分简单高效。类文件的常量池条目将合并到运行时常量池中，因此外部和内部量访问的是同一个常量。
下面的Bytecodes表示内部类中直接将常量池中的常量压栈后作为返回值返回。
java.lang.String getName();
flags:
Code:
stack=, locals=, args_size=
: ldc # // String fsjohnhuang
: areturn
LineNumberTable:
line :
五、匿名内部类
匿名内部类其实是局部内部类的特殊形式。一般用来绑定事件监听处理程序上。Android示例：
class Outer{
public void subs(){
scan_bt.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub }
});
}
}
上述代码生成了一个继承OnClickListener类的匿名内部类，然后实例化匿名类的一个实例，然后以该实例作为参数调用setOnClickListener方法。
并生成一个Outer.class和Outer$1.class类文件。
注意事项与局部内部一样。
六、静态内部类
静态内部类定义在类下，只不过多了个关键字static。静态内部类只能访问外部类的静态字段和静态方法。
而实例化静态内部类时只需 new 外部类.静态内部类() 。
七、总结
尊重原创，转载请注明来自：http://www.cnblogs.com/fsjohnhuang/p/4270044.html ^_^肥仔John
八、参考
http://www.cnblogs.com/dolphin0520/p/3811445.html
