标签：
1.产生
源码（.java文件）——>编译器（如：javac）——>字节码（.class文件）——>虚拟机（如：HotSpot）执行
2.Class文件
1）构成：
2）例子：
[1] .java文件
桌面/test/test/Father.java、桌面/test/test/Father_interface.java、桌面/test/Son.java ;
[2]编译出.class文件
cd 桌面/test;
桌面/test>javac Son.java;
[3]查看.class文件
桌面/test>javap -verbose Son;
Classfile /C:/Users/Administrator/Desktop/test/Son.class Last modified 2016-4-11; size 1005 bytes MD5 checksum 7d138d76267a6bb372eba05296e2c932魔数 Compiled from "Son.java" public class test.Son extends test.Father implements test.Father_interface索引（1类索引、2父类索引、3接口索引，指向常量池） SourceFile: "Son.java" minor version: 0 major version: 51主板本号 flags: ACC_PUBLIC, ACC_SUPER访问标志<当前类> Constant pool:常量池 #1 = Methodref #16.#33 // test/Father."<init>":()V 符号引用{ #2 = Fieldref #15.#34 // test/Son.sId_literal:I #3 = Fieldref #35.#36 // java/lang/System.out:Ljava/io/PrintStream; #4 = Class #37 // java/lang/StringBuilder #5 = Methodref #4.#33 // java/lang/StringBuilder."<init>":()V #6 = String #38 // statical_sId = #7 = Methodref #4.#39 // java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/Strin gBuilder; #8 = Fieldref #15.#40 // test/Son.statical_sId:I #9 = Methodref #4.#41 // java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder; #10 = Methodref #4.#42 // java/lang/StringBuilder.toString:()Ljava/lang/String; #11 = Methodref #43.#44 // java/io/PrintStream.println:(Ljava/lang/String;)V #12 = String #45 // Son实例构造器! #13 = String #46 // hello!this is son! #14 = String #47 // Son类构造器<clinit>执行! #15 = Class #48 // test/Son 1 #16 = Class #49 // test/Father 2 #17 = Class #50 // test/Father_interface 3 ｝符号引用 #18 = Utf8 final_sId #19 = Utf8 I #20 = Utf8 ConstantValue #21 = Integer 123 字面量 #22 = Utf8 statical_sId #23 = Utf8 sId_literal #24 = Utf8 sId_nonLiteral #25 = Utf8 <init> #26 = Utf8 ()V #27 = Utf8 Code #28 = Utf8 LineNumberTable #29 = Utf8 sayHello #30 = Utf8 <clinit> #31 = Utf8 SourceFile #32 = Utf8 Son.java 符号引用{ #33 = NameAndType #25:#26 // "<init>":()V #34 = NameAndType #23:#19 // sId_literal:I #35 = Class #51 // java/lang/System #36 = NameAndType #52:#53 // out:Ljava/io/PrintStream; #37 = Utf8 java/lang/StringBuilder #38 = Utf8 statical_sId = #39 = NameAndType #54:#55 // append:(Ljava/lang/String;)Ljava/lang/StringBuilder; #40 = NameAndType #22:#19 // statical_sId:I #41 = NameAndType #54:#56 // append:(I)Ljava/lang/StringBuilder; #42 = NameAndType #57:#58 // toString:()Ljava/lang/String; #43 = Class #59 // java/io/PrintStream #44 = NameAndType #60:#61 // println:(Ljava/lang/String;)V #45 = Utf8 Son实例构造器! }符号引用 #46 = Utf8 hello!this is son! #47 = Utf8 Son类构造器<clinit>执行! #48 = Utf8 test/Son #49 = Utf8 test/Father #50 = Utf8 test/Father_interface #51 = Utf8 java/lang/System #52 = Utf8 out #53 = Utf8 Ljava/io/PrintStream; #54 = Utf8 append #55 = Utf8 (Ljava/lang/String;)Ljava/lang/StringBuilder; #56 = Utf8 (I)Ljava/lang/StringBuilder; #57 = Utf8 toString #58 = Utf8 ()Ljava/lang/String; #59 = Utf8 java/io/PrintStream #60 = Utf8 println #61 = Utf8 (Ljava/lang/String;)V { public test.Son();方法表——实例构造器 flags: ACC_PUBLIC Code: stack=3, locals=1, args_size=1 0: aload_0 1: invokespecial #1 // Method test/Father."<init>":()V 4: aload_0 5: bipush 123 7: putfield #2 // Field sId_literal:I 10: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 13: new #4 // class java/lang/StringBuilder 16: dup 17: invokespecial #5 // Method java/lang/StringBuilder."<init>":()V 20: ldc #6 // String statical_sId = 22: invokevirtual #7 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/ lang/StringBuilder; 25: getstatic #8 // Field statical_sId:I 28: invokevirtual #9 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilde r; 31: invokevirtual #10 // Method java/lang/StringBuilder.toString:()Ljava/lang/String; 34: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 37: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 40: ldc #12 // String Son实例构造器! 42: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 45: sipush 333 48: putstatic #8 // Field statical_sId:I 51: return LineNumberTable: line 15: 0 line 7: 4 line 16: 10 line 17: 37 line 18: 45 line 19: 51 public void sayHello();方法表——sayHello() flags: ACC_PUBLIC Code: stack=2, locals=1, args_size=1 0: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #13 // String hello!this is son! 5: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 8: return LineNumberTable: line 21: 0 line 22: 8 static {};方法表——类构造器（或静态代码块） flags: ACC_STATIC Code: stack=3, locals=0, args_size=0 0: bipush 123 2: putstatic #8 // Field statical_sId:I 5: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 8: new #4 // class java/lang/StringBuilder 11: dup 12: invokespecial #5 // Method java/lang/StringBuilder."<init>":()V 15: ldc #6 // String statical_sId = 17: invokevirtual #7 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/ lang/StringBuilder; 20: getstatic #8 // Field statical_sId:I 23: invokevirtual #9 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilde r; 26: invokevirtual #10 // Method java/lang/StringBuilder.toString:()Ljava/lang/String; 29: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 32: getstatic #3 // Field java/lang/System.out:Ljava/io/PrintStream; 35: ldc #14 // String Son类构造器<clinit>执行! 37: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 40: return LineNumberTable: line 6: 0 line 11: 5 line 12: 32 line 13: 40 }
3.总结
魔数、版本号、常量池、访问标志、索引、字段表集合、方法表集合
| 魔数 | 版本号 | 常量池 | 访问标志 | 索引 | 字段表集合 | 方法表集合 |
|
后缀名是可以改的， 所以用它来确定真 的是.class文件 |
44=JDK1.0 45=jdk1.1 .... |
字面量：int、double等基本类型数据值 符号引用：（最终指向UTF-8字符串） 1）记录类 访问标志+全限定名 2）记录方法 简单名称+返回类型+参数列表 3）记录成员属性 简单名称+返回类型
|
分为：本类、继承父类类、实现接口 指向“常量池—记录类” |
每张表： 访问标志、（名称、描述【如：返回类型、参数等】）、附加属性attributes（Code属性表、Linumber属性表、局部变量表、异常表等） /** 括号中表示是指向“常量池”*/
|
读《深入理解Java虚拟机》有感——第一部分：Class文件的结构
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原文地址：http://www.cnblogs.com/crazyYouth/p/5376908.html
