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java文件

package com.kq.jvm;public class SimpleDemo {    private long id;    public String name;}

javap解析文件

 

class文件

00000000: CA FE BA BE 00 00 00 34 00 14 0A 00 03 00 11 07    J~:>...4........00000010: 00 12 07 00 13 01 00 02 69 64 01 00 01 4A 01 00    ........id...J..00000020: 04 6E 61 6D 65 01 00 12 4C 6A 61 76 61 2F 6C 61    .name...Ljava/la00000030: 6E 67 2F 53 74 72 69 6E 67 3B 01 00 06 3C 69 6E    ng/String;...
   
    ...()V...Code00000050: 01 00 0F 4C 69 6E 65 4E 75 6D 62 65 72 54 61 62    ...LineNumberTab00000060: 6C 65 01 00 12 4C 6F 63 61 6C 56 61 72 69 61 62    le...LocalVariab00000070: 6C 65 54 61 62 6C 65 01 00 04 74 68 69 73 01 00    leTable...this..00000080: 17 4C 63 6F 6D 2F 6B 71 2F 6A 76 6D 2F 53 69 6D    .Lcom/kq/jvm/Sim00000090: 70 6C 65 44 65 6D 6F 3B 01 00 0A 53 6F 75 72 63    pleDemo;...Sourc000000a0: 65 46 69 6C 65 01 00 0F 53 69 6D 70 6C 65 44 65    eFile...SimpleDe000000b0: 6D 6F 2E 6A 61 76 61 0C 00 08 00 09 01 00 15 63    mo.java........c000000c0: 6F 6D 2F 6B 71 2F 6A 76 6D 2F 53 69 6D 70 6C 65    om/kq/jvm/Simple000000d0: 44 65 6D 6F 01 00 10 6A 61 76 61 2F 6C 61 6E 67    Demo...java/lang000000e0: 2F 4F 62 6A 65 63 74 00 21 00 02 00 03 00 00 00    /Object.!.......000000f0: 02 00 02 00 04 00 05 00 00 00 01 00 06 00 07 00    ................00000100: 00 00 01 00 01 00 08 00 09 00 01 00 0A 00 00 00    ................00000110: 2F 00 01 00 01 00 00 00 05 2A B7 00 01 B1 00 00    /........*7..1..00000120: 00 02 00 0B 00 00 00 06 00 01 00 00 00 08 00 0C    ................00000130: 00 00 00 0C 00 01 00 00 00 05 00 0D 00 0E 00 00    ................00000140: 00 01 00 0F 00 00 00 02 00 10                      ..........
   

magic - u4

0xCAFEBABE

CA FE BA BE

minor_version - u2

次版本号

00 00

major_version - u2

主版本号

# 00 3452 是 jdk1.8

constant_pool_count - u2

常量池个数

第一个是null

# 00 14常量池20个

constant_pool

第1个常量池 0A

0A是10，是CONSTANT_Methodref

CONSTANT_Methodref_info {    u1 tag;    u2 class_index;    u2 name_and_type_index;}

# 0A 00 03 00 11指向 03  和  17

第2个常量池 07

07类型是CONSTANT_Class

CONSTANT_Class_info {    u1 tag;    u2 name_index;}

07 00 12# name_index=#18

 

第3个常量池 07

同上第2个常量

07 00 13# name_index=#19

第4个常量池   01

01是CONSTANT_Utf8

CONSTANT_Utf8_info {    u1 tag;    u2 length;    u1 bytes[length];}

# 01 00 02 69 64tag=01length=00 0202后面取2位，就是bytes数据 (6964=id)

第5个常量池    01

同上

# 01 00 01 4A4A = J

第6个常量池  01

同上

# 01 00 04 6E 61 6D 656E = n61 = a6D = m65 = e

 

第7个常量池  01

同上

# 18个01 00 12  # Ljava/lang/String;4c 6a 61 76 61 2f 6c 61 6e 67 2f 53 74 72 69 6e 67 3b

 

第8个常量池  01

同上

# 6个01 00 06 # 
   
    3c 69 6e 69 74 3e
   

 

第9个常量池  01

同上

# 3个01 00 03# ()V28 29 56

第10个常量池  01

同上

# 4个01 00 04# Code43 6F 64 65

 

第11个常量池  01

同上

# 15个01 00 0f# LineNumberTable4C 69 6E 65 4E 75 6D 62 65 72 54 61 62 6C 65

 

第12个常量池  01

同上

# 18个01 00 12# LocalVariableTable4C 6F 63 61 6C 56 61 72 69 61 62 6C 65 54 61 62 6C 65

 

第13个常量池  01

同上

# 4个01 00 04# this74 68 69 73

 

第14个常量池  01

同上

# 23个01 00 17# Lcom/kq/jvm/SimpleDemo;4C 63 6F 6D 2F 6B 71 2F 6A 76 6D 2F 53 69 6D 70 6C 65 44 65 6D 6F 3B

 

第15个常量池  01

同上

# 10个01 00 0A# SourceFile53 6F 75 72 63 65 46 69 6C 65

 

第16个常量池  01

同上

# 15个01 00 0F# SimpleDemo.java53 69 6D 70 6C 65 44 65 6D 6F 2E 6A 61 76 61

 

第17个常量池  0C

CONSTANT_NameAndType_info {    u1 tag;    u2 name_index;    u2 descriptor_index;}

The value of the name_index item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_Utf8_info structure 

The value of the descriptor_index item must be a valid index into the constant_pool table. The constant_pool entry at that index must be a CONSTANT_Utf8_info structure

0C 00 08 00 09name_index = #8 (常量池第8个位置)descriptor_index = #9 (常量池第9个位置)

 

第18个常量池  01

CONSTANT_Utf8_info

# 21个01 00 15# com/kq/jvm/SimpleDemo63 6F 6D 2F 6B 71 2F 6A 76 6D 2F 53 69 6D 70 6C 65 44 65 6D 6F

 

第19个常量池  01

CONSTANT_Utf8_info

# 16个位置01 00 10# java/lang/Object6A 61 76 61 2F 6C 61 6E 67 2F 4F 62 6A 65 63 74

 

access_flags u2

# 3300 21

 

this_class u2

com/kq/jvm/SimpleDemo

#  #2 第2个常量池00 02

access_flags下面的两个字节叫做this_class， 它是对当前类的描述。 

它的两个字节的数据是对常量池中的一个CONSTANT_Class_info数据项的一个索引。 

CONSTANT_Class_info中有一个字段叫做name_index , 指向一个CONSTANT_Utf8_info,

在这个CONSTANT_Utf8_info 中存放着当前类的全限定名

 

super_class u2

java/lang/Object

# 03 第3个常量池00 03

 

interfaces_count  u2

# 0个接口00 00

interfaces u2

Each value in the interfaces array must be a valid index into the constant_pool table. The constant_pool entry at each value of interfaces[i], where 0 ≤ i < interfaces_count, must be a CONSTANT_Class_info structure representing an interface that is a direct superinterface of this class or interface type, in the left-to-right order given in the source for the type.

u2  interfaces[interfaces_count];

没有实现任何接口，所以interfaces_count=0，这时候也就没有interfaces[]了

fields_count u2

# 2个field00 02

 

fields[] 

field_info {    u2             access_flags;    u2             name_index;    u2             descriptor_index;    u2             attributes_count;    attribute_info attributes[attributes_count];}

field[0]

field[0] - access_flags - u2

private

ACC_PRIVATE

0x0002

Declared private; usable only within the defining class.

# private00 02

field[0] - name_index - u2

id

# 常量池第4个位置00 04

field[0] - descriptor_index - u2

# 常量池第5个位置  是J  是long类型00 05

 

field[0] - attributes_count - u2

# 0个attributes_count00 00

 

field[0] - attribute_info attributes[attributes_count]

由于上面是0，这里不占空间

 

field[1]

 

field[1] - access_flags - u2

public

ACC_PUBLIC

0x0001

Declared public; may be accessed from outside its package.

# public00 01

field[1] - name_index - u2

name

# 常量池第6个位置00 06

field[1] - descriptor_index - u2

L ClassName ;

reference

an instance of class ClassName

# 常量池第7个位置  是Ljava/lang/String;类型00 07

 

field[1] - attributes_count - u2

# 0个attributes_count00 00

 

field[1] - attribute_info attributes[attributes_count]

由于上面是0，这里不占空间

 

methods_count

# 1个方法00 01

 

method

method_info {    u2             access_flags;    u2             name_index;    u2             descriptor_index;    u2             attributes_count;    attribute_info attributes[attributes_count];}

method[0] - access_flags u2

public

ACC_PUBLIC

0x0001

Declared public; may be accessed from outside its package.

# public00 01

method[0] - name_index u2

# 第8个位置00 08

 

method[0] - descriptor_index u2

# 常量池第9个位置00 09

 

method[0] - attributes_count  u2

# attributes_count有1个00 01

 

method[0] - attributes

attribute_info {    u2 attribute_name_index;    u4 attribute_length;    u1 info[attribute_length];}

 

method[0] - attributes - attribute_name_index - u2

# 常量池第10个位置  Code00 0A

 

method[0] - attributes - attribute_length - u4

# length = 32+15 = 4700 00 00 2F

Code_attribute

Code_attribute {    u2 attribute_name_index;    u4 attribute_length;    u2 max_stack;    u2 max_locals;    u4 code_length;   # 指令长度是多少 假设是5  往后数5个字节    u1 code[code_length];   # 2A B7 00 01 B1    u2 exception_table_length;    {   u2 start_pc;        u2 end_pc;        u2 handler_pc;        u2 catch_type;    } exception_table[exception_table_length];    u2 attributes_count;    attribute_info attributes[attributes_count];}

 

method[0] - attributes - info[attribute_length]

# 47   00 01 00 01 00 00 00 05 2A B7 00 01 B1 00 0000 02 00 0B 00 00 00 06 00 01 00 00 00 08 00 0C00 00 00 0C 00 01 00 00 00 05 00 0D 00 0E 00 00

attribute_length项的值表示属性的长度，不包括前六个字节（不包括attribute_name_index、attribute_length），也就是从max_stack开始

max_stack = 00 01 = 1max_locals = 00 01 = 1u4 code_length = 00 00 00 05 = 5

code[code_length] = 2A B7 00 01 B1aload_0 = 42 (0x2a)invokespecial = 183 (0xb7)  # 后面2位是操作那个对象00 01  #1 
   
    >return = 177 (0xb1)
   

 

method - exception_table_length - u2

# 0个exception00 00

 

attributes_count

# 2个00 02

LineNumberTable 

attributes - attribute_name_index - u2

# LineNumberTable00 0B

LineNumberTable_attribute {    u2 attribute_name_index;    u4 attribute_length;    u2 line_number_table_length;  # 有下面这样的几组    {   u2 start_pc;  # 指令码的行数          u2 line_number;	  # 源码的行号    } line_number_table[line_number_table_length];}

# attribute_length00 00 00 06# 00 01   1组line_number_table_length# start_pc  0 00 00# line_number 8 00 08

 

LocalVariableTable

# 1200 0C

LocalVariableTable_attribute {    u2 attribute_name_index;    u4 attribute_length;    u2 local_variable_table_length;    {   u2 start_pc;        u2 length;        u2 name_index;        u2 descriptor_index;        u2 index;    } local_variable_table[local_variable_table_length];}

 

attribute_length

# 1200 00 00 0C

 

00 01 00 00 00 05 00 0D 00 0E 00 00local_variable_table_length = 00 01 = 1u2 start_pc = 00 00 = 0u2 length = 00 05 = 5u2 name_index = 00 0D = #13 = thisu2 descriptor_index = 00 0E = #14 = Lcom/kq/jvm/SimpleDemo;u2 index = 00 00

 

 

 

class - attributes_count - u2

# 1个00 01

 

class - attribute_info 

attribute_info {    u2 attribute_name_index;  # 00 0F = 15    u4 attribute_length;  #  00 00 00 02  2字节    u1 info[attribute_length];   # 00 10 = 16}

 

 

 

 

 

 

 

 

 

 

 

 

 

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