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publicclasstest{privatestaticintclassV=2;publicstaticvoidmain(String[]args){classV=200;intlocalV=4;localV=400;}}javap 指令和选项0:无选项

打印package,protectedandpublicfields,andmethodspublicclasscom.example.test{publiccom.example.test();publicstaticvoidmain(java.lang.String[]);static{};}1：辅助指令

-help
–help
-?

-l

publicclasscom.example.test{//默认构造方法publiccom.example.test();//代码行号：命令偏移位置LineNumberTable:line3:0//局部变量表LocalVariableTable:StartLengthSlotNameSignature050thisLcom/example/test;publicstaticvoidmain(java.lang.String[]);//代码行号：命令偏移位置LineNumberTable:line6:0line7:6line8:8line9:12//局部变量表LocalVariableTable:StartLengthSlotNameSignature0130args[Ljava/lang/String;//方法参数851localVI。/局部变量localV//静态代码块static{};LineNumberTable:line4:0}3 用级别过滤方法 属性 类

-public
-protected
-private
-p

javap -c

//纯汇编指令publicclasscom.example.test{publiccom.example.test();Code:0:aload_01:invokespecial#1//Methodjava/lang/Object."<init>":()V4:returnpublicstaticvoidmain(java.lang.String[]);Code:0:sipush2003:putstatic#2//FieldclassV:I6:iconst_47:istore_18:sipush40011:istore_112:returnstatic{};Code:0:iconst_21:putstatic#2//FieldclassV:I4:return}5 显示verbose详细信息

javap -v

Classfile /Users/zhangshanxue/Downloads/akka-quickstart-java/target/classes/com/example/test.class//javap -sysinfo显示下面3行 Last modified 2021-4-5; size 507 bytes MD5 checksum 24a0c74751aafd61d0f7f69be9c161db Compiled from "test.java"public class com.example.test//即1.8 对照表和原因见附录1 //u2类型 即每个占用两个字节 minor version: 0 major version: 52 //类标志 见附录2 //u2类型access_flags 通过位与表示多个权限 flags: ACC_PUBLIC, ACC_SUPER //常量池。class文件结构重点 //u2 2两个字节 表示数量//pool 常量池//constant_pool_count 和constant_pool[]表示为常量池中内容//后面大部分内容依赖此常量池Constant pool: #1 = Methodref #4.#22 // java/lang/Object."<init>":()V #2 = Fieldref #3.#23 // com/example/test.classV:I #3 = Class #24 // com/example/test #4 = Class #25 // java/lang/Object #5 = Utf8 classV #6 = Utf8 I #7 = Utf8 <init> #8 = Utf8 ()V #9 = Utf8 Code #10 = Utf8 LineNumberTable #11 = Utf8 LocalVariableTable #12 = Utf8 this #13 = Utf8 Lcom/example/test; #14 = Utf8 main #15 = Utf8 ([Ljava/lang/String;)V #16 = Utf8 args #17 = Utf8 [Ljava/lang/String; #18 = Utf8 localV #19 = Utf8 <clinit> #20 = Utf8 SourceFile #21 = Utf8 test.java #22 = NameAndType #7:#8 // "<init>":()V #23 = NameAndType #5:#6 // classV:I #24 = Utf8 com/example/test #25 = Utf8 java/lang/Object{ public com.example.test(); descriptor: ()V flags: ACC_PUBLIC Code: //代码汇编指令 stack=1, locals=1, args_size=1 0: aload_0 1: invokespecial #1 // Method java/lang/Object."<init>":()V 4: return //Javap -l显示下面信息 //行号和上面对应的指令偏移位置 LineNumberTable: line 3: 0 LocalVariableTable: //局部变量表 在指令偏移位置start start+length之间有效 Start Length Slot Name Signature 0 5 0 this Lcom/example/test; public static void main(java.lang.String[]); descriptor: ([Ljava/lang/String;)V flags: ACC_PUBLIC, ACC_STATIC Code: //代码汇编指令 stack=1, locals=2, args_size=1 0: sipush 200 3: putstatic #2 // Field classV:I 6: iconst_4 7: istore_1 8: sipush 400 11: istore_1 12: return //Javap -l显示下面信息 //行号和上面对应的指令偏移位置 LineNumberTable: line 6: 0 line 7: 6 line 8: 8 line 9: 12 LocalVariableTable: Start Length Slot Name Signature 0 13 0 args [Ljava/lang/String; 8 5 1 localV I static {}; descriptor: ()V flags: ACC_STATIC Code: stack=1, locals=0, args_size=0 0: iconst_2 1: putstatic #2 // Field classV:I 4: return //行号和上面对应的指令偏移位置 LineNumberTable: line 4: 0


直接分析字节码块

1为了方便交流表达class文件的结构

使用u1 u2 u4 u8无符号数表示字节数使用*_info 结尾表示池（数组cp_info、field_info、method_info、attribute_info

ClassFile{//表示javaclass的文件格式固定为cafebaby4个字节u4magic;//主版本号和次版本号共同决定了类文件格式的版本//u2类型即每个占用两个字节//56包含56以后supportforN.0andN.65535u2minor_version;//主版本号56（java12）之前minjor只支持0u2major_version;//常量池数量u2constant_pool_count;cp_infoconstant_pool[constant_pool_count-1];u2access_flags;//this_class、super_class、interfaces指向常量池的CONSTANT_Class_infou2this_class;u2super_class;u2interfaces_count;u2interfaces[interfaces_count];u2fields_count;//指向常量池structures:CONSTANT_Fieldref_info结构field_infofields[fields_count];u2methods_count;//指向常量池CONSTANT_Methodref_info结构method_infomethods[methods_count];u2attributes_count;attribute_infoattributes[attributes_count];}

感谢各位的阅读，以上就是“java如何拆解字节码文件”的内容了，经过本文的学习后，相信大家对java如何拆解字节码文件这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！