javap定义

javap是 Java class文件分解器，可以反编译（即对javac编译的文件进行反编译），也可以查看java编译器生成的字节码。用于分解class文件。

测试类

  1. public class JavapTest {
  3.     private static final int _P_1 = 1;
  4.     public static final int _P_2 = 2;
  6.     public static void main(String[] args) {
  7.         int m = 0, n = 0;
  8.         for (int i = 0; i < 10; i++) {
  9.             m = m++;
  10.             n = ++n;
  11.         }
  12.         System.out.println("m = " + m);
  13.         System.out.println("n = " + n);
  14.     }
  15. }

javap命令参数

  1. C:\Users\l>javap -help
  2. 用法: javap <options> <classes>
  3. 其中, 可能的选项包括:
  4.   -? -h --help -help               输出此帮助消息
  5.   -version                         版本信息
  6.   -v  -verbose                     输出附加信息
  7.   -l                               输出行号和本地变量表
  8.   -public                          仅显示公共类和成员
  9.   -protected                       显示受保护的/公共类和成员
  10.   -package                         显示程序包/受保护的/公共类
  11.                                    和成员 (默认)
  12.   -p  -private                     显示所有类和成员
  13.   -c                               对代码进行反汇编
  14.   -s                               输出内部类型签名
  15.   -sysinfo                         显示正在处理的类的
  16.                                    系统信息 (路径, 大小, 日期, MD5 散列)
  17.   -constants                       显示最终常量
  18.   --module <模块>, -m <模块>       指定包含要反汇编的类的模块
  19.   --module-path <路径>             指定查找应用程序模块的位置
  20.   --system <jdk>                   指定查找系统模块的位置
  21.   --class-path <路径>              指定查找用户类文件的位置
  22.   -classpath <路径>                指定查找用户类文件的位置
  23.   -cp <路径>                       指定查找用户类文件的位置
  24.   -bootclasspath <路径>            覆盖引导类文件的位置
  26. GNU 样式的选项可使用 = (而非空白) 来分隔选项名称
  27. 及其值。
  29. 每个类可由其文件名, URL 或其
  30. 全限定类名指定。示例:
  31.    path/to/MyClass.class
  32.    jar:file:///path/to/MyJar.jar!/mypkg/MyClass.class
  33.    java.lang.Object

javap -version:显示java版本

  1. 11.0.14

javap -p:显示所有类和成员

  1. D:\Source\beike_one\JAVASE_02>javap -p JavapTest.class
  2. Compiled from "JavapTest.java"
  3. public class JavapTest {
  4.   private static final int _P_1;
  5.   public static final int _P_2;
  6.   public JavapTest();
  7.   public static void main(java.lang.String[]);

javap -public:仅显示公共类和成员

  1. D:\Source\beike_one\JAVASE_02>javap -public JavapTest.class
  2. Compiled from "JavapTest.java"
  3. public class JavapTest {
  4.   public static final int _P_2;
  5.   public JavapTest();
  6.   public static void main(java.lang.String[]);
  7. }

javap -l:输出行号和本地变量表

  1. D:\Source\beike_one\JAVASE_02>javap -p -l JavapTest.class
  2. Compiled from "JavapTest.java"
  3. public class JavapTest {
  4.   private static final int _P_1;
  6.   public static final int _P_2;
  8.   public JavapTest();
  9.     LineNumberTable:
  10.       line 1: 0
  12.   public static void main(java.lang.String[]);
  13.     LineNumberTable:
  14.       line 7: 0
  15.       line 8: 4
  16.       line 9: 12
  17.       line 10: 17
  18.       line 8: 22
  19.       line 12: 28
  20.       line 13: 40
  21.       line 14: 52
  22. }

javap -v/-p -v:

这是两个命令：
javap -v JavapTest.class
或者
javap -p -v JavapTest.class

命令说明是：
输出附加信息class文件的路径
最后修改时间
文件大小等类的全路径
源（java）文件等常量池常量定义
值构造方法程序调用及执行逻辑（这个涉及的内容就比较多了）

  1. D:\Source\beike_one\JAVASE_02>javap -p -v JavapTest.class
  2. Classfile /D:/Source/beike_one/JAVASE_02/JavapTest.class
  3.   Last modified 2022年3月9日; size 1039 bytes
  4.   MD5 checksum fa1231c69dc6eca6a29a533e2f027c0a
  5.   Compiled from "JavapTest.java"
  6. public class JavapTest
  7.   minor version: 0
  8.   major version: 55
  9.   flags: (0x0021) ACC_PUBLIC, ACC_SUPER
  10.   this_class: #6                          // JavapTest
  11.   super_class: #7                         // java/lang/Object
  12.   interfaces: 0, fields: 2, methods: 2, attributes: 3
  13. Constant pool:
  14.    #1 = Methodref          #7.#23         // java/lang/Object."<init>":()V
  15.    #2 = Fieldref           #24.#25        // java/lang/System.out:Ljava/io/PrintStream;
  16.    #3 = InvokeDynamic      #0:#29         // #0:makeConcatWithConstants:(I)Ljava/lang/String;
  17.    #4 = Methodref          #30.#31        // java/io/PrintStream.println:(Ljava/lang/String;)V
  18.    #5 = InvokeDynamic      #1:#29         // #1:makeConcatWithConstants:(I)Ljava/lang/String;
  19.    #6 = Class              #33            // JavapTest
  20.    #7 = Class              #34            // java/lang/Object
  21.    #8 = Utf8               _P_1
  22.    #9 = Utf8               I
  23.   #10 = Utf8               ConstantValue
  24.   #11 = Integer            1
  25.   #12 = Utf8               _P_2
  26.   #13 = Integer            2
  27.   #14 = Utf8               <init>
  28.   #15 = Utf8               ()V
  29.   #16 = Utf8               Code
  30.   #17 = Utf8               LineNumberTable
  31.   #18 = Utf8               main
  32.   #19 = Utf8               ([Ljava/lang/String;)V
  33.   #20 = Utf8               StackMapTable
  34.   #21 = Utf8               SourceFile
  35.   #22 = Utf8               JavapTest.java
  36.   #23 = NameAndType        #14:#15        // "<init>":()V
  37.   #24 = Class              #35            // java/lang/System
  38.   #25 = NameAndType        #36:#37        // out:Ljava/io/PrintStream;
  39.   #26 = Utf8               BootstrapMethods
  40.   #27 = MethodHandle       6:#38          // REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  41.   #28 = String             #39            // m = \u0001
  42.   #29 = NameAndType        #40:#41        // makeConcatWithConstants:(I)Ljava/lang/String;
  43.   #30 = Class              #42            // java/io/PrintStream
  44.   #31 = NameAndType        #43:#44        // println:(Ljava/lang/String;)V
  45.   #32 = String             #45            // n = \u0001
  46.   #33 = Utf8               JavapTest
  47.   #34 = Utf8               java/lang/Object
  48.   #35 = Utf8               java/lang/System
  49.   #36 = Utf8               out
  50.   #37 = Utf8               Ljava/io/PrintStream;
  51.   #38 = Methodref          #46.#47        // java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  52.   #39 = Utf8               m = \u0001
  53.   #40 = Utf8               makeConcatWithConstants
  54.   #41 = Utf8               (I)Ljava/lang/String;
  55.   #42 = Utf8               java/io/PrintStream
  56.   #43 = Utf8               println
  57.   #44 = Utf8               (Ljava/lang/String;)V
  58.   #45 = Utf8               n = \u0001
  59.   #46 = Class              #48            // java/lang/invoke/StringConcatFactory
  60.   #47 = NameAndType        #40:#52        // makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  61.   #48 = Utf8               java/lang/invoke/StringConcatFactory
  62.   #49 = Class              #54            // java/lang/invoke/MethodHandles$Lookup
  63.   #50 = Utf8               Lookup
  64.   #51 = Utf8               InnerClasses
  65.   #52 = Utf8               (Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  66.   #53 = Class              #55            // java/lang/invoke/MethodHandles
  67.   #54 = Utf8               java/lang/invoke/MethodHandles$Lookup
  68.   #55 = Utf8               java/lang/invoke/MethodHandles
  69. {
  70.   private static final int _P_1;
  71.     descriptor: I
  72.     flags: (0x001a) ACC_PRIVATE, ACC_STATIC, ACC_FINAL
  73.     ConstantValue: int 1
  75.   public static final int _P_2;
  76.     descriptor: I
  77.     flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL
  78.     ConstantValue: int 2
  80.   public JavapTest();
  81.     descriptor: ()V
  82.     flags: (0x0001) ACC_PUBLIC
  83.     Code:
  84.       stack=1, locals=1, args_size=1
  85.          0: aload_0
  86.          1: invokespecial #1                  // Method java/lang/Object."<init>":()V
  87.          4: return
  88.       LineNumberTable:
  89.         line 1: 0
  91.   public static void main(java.lang.String[]);
  92.     descriptor: ([Ljava/lang/String;)V
  93.     flags: (0x0009) ACC_PUBLIC, ACC_STATIC
  94.     Code:
  95.       stack=2, locals=4, args_size=1
  96.          0: iconst_0
  97.          1: istore_1
  98.          2: iconst_0
  99.          3: istore_2
  100.          4: iconst_0
  101.          5: istore_3
  102.          6: iload_3
  103.          7: bipush        10
  104.          9: if_icmpge     28
  105.         12: iload_1
  106.         13: iinc          1, 1
  107.         16: istore_1
  108.         17: iinc          2, 1
  109.         20: iload_2
  110.         21: istore_2
  111.         22: iinc          3, 1
  112.         25: goto          6
  113.         28: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
  114.         31: iload_1
  115.         32: invokedynamic #3,  0              // InvokeDynamic #0:makeConcatWithConstants:(I)Ljava/lang/String;
  116.         37: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  117.         40: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
  118.         43: iload_2
  119.         44: invokedynamic #5,  0              // InvokeDynamic #1:makeConcatWithConstants:(I)Ljava/lang/String;
  120.         49: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  121.         52: return
  122.       LineNumberTable:
  123.         line 7: 0
  124.         line 8: 4
  125.         line 9: 12
  126.         line 10: 17
  127.         line 8: 22
  128.         line 12: 28
  129.         line 13: 40
  130.         line 14: 52
  131.       StackMapTable: number_of_entries = 2
  132.         frame_type = 254 /* append */
  133.           offset_delta = 6
  134.           locals = [ int, int, int ]
  135.         frame_type = 250 /* chop */
  136.           offset_delta = 21
  137. }
  138. SourceFile: "JavapTest.java"
  139. InnerClasses:
  140.   public static final #50= #49 of #53;    // Lookup=class java/lang/invoke/MethodHandles$Lookup of class java/lang/invoke/MethodHandles
  141. BootstrapMethods:
  142.   0: #27 REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  143.     Method arguments:
  144.       #28 m = \u0001
  145.   1: #27 REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
  146.     Method arguments:
  147.       #32 n = \u0001

javap -c:对代码进行反汇编

javap-c输出内部javap-v中已经有了，我们详细介绍下javap-c命令的输出内容0:iconst_0前面0:表示执行的顺序，iconst_0把值0放入栈顶，_0中的0代表压栈的值，如：iconst_5，即把5压入栈顶1:istore_1将栈顶的值放入变量1中，_1代表变量的序列，本例中为：m，如：istore_2即为变量n赋值6:iload_3将变量3即i的的值放入栈顶，与iconst不同的是，iload操作的值是已经定义好存在的值，iconst是定义时的压栈操作13:iinc1,1将变量1的值加1

  1. D:\Source\beike_one\JAVASE_02>javap -c JavapTest.class
  2. Compiled from "JavapTest.java"
  3. public class JavapTest {
  4.   public static final int _P_2;
  6.   public JavapTest();
  7.     Code:
  8.        0: aload_0
  9.        1: invokespecial #1                  // Method java/lang/Object."<init>":()V
  10.        4: return
  12.   public static void main(java.lang.String[]);
  13.     Code:
  14.        0: iconst_0
  15.        1: istore_1
  16.        2: iconst_0
  17.        3: istore_2
  18.        4: iconst_0
  19.        5: istore_3
  20.        6: iload_3
  21.        7: bipush        10
  22.        9: if_icmpge     28
  23.       12: iload_1
  24.       13: iinc          1, 1
  25.       16: istore_1
  26.       17: iinc          2, 1
  27.       20: iload_2
  28.       21: istore_2
  29.       22: iinc          3, 1
  30.       25: goto          6
  31.       28: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
  32.       31: iload_1
  33.       32: invokedynamic #3,  0              // InvokeDynamic #0:makeConcatWithConstants:(I)Ljava/lang/String;
  34.       37: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  35.       40: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
  36.       43: iload_2
  37.       44: invokedynamic #5,  0              // InvokeDynamic #1:makeConcatWithConstants:(I)Ljava/lang/String;
  38.       49: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
  39.       52: return
  40. }