javap 工具是检索特定类或接口信息的有用方法。通过其反汇编功能，javap 命令（也称为 Java 反汇编器）被赋予了为用户提供全面的内部信息的作用。从 -c 或 -verbose 这两个选项中，每个选项都会给出独特的结果，用户能够发现自己处于字节码和字节码编排领域。如果不使用任何选项，javap 会运行输入类的 public、protected 和 package 字段和方法。
语法
javap [option] [classname]
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不使用选项时
示例
javap class_name
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输出
C:UsersAashi>javap java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException; public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
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何时使用选项
以下是每个选项以及如何应用它的说明 -
-
-help 或 --help 或 -? -
这用于打印 javap 命令的帮助消息。
示例
javap -help
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输出
C:UsersAashi>javap -help
Usage: javap
where possible options include:
-help --help -? Print this usage message
-version Version information
-V -verbose Print additional information
-1 Print line number and local variable tables
-public Show only public classes and members
-protected Show protected/public classes and members
-package Show package/protected/public classes and members (default)
-p -private Show all classes and members
-C Disassemble the code
-S Print internal type signatures
-sysinfo Show system info (path, size, date, MD5 hash) of class being processed
-constants Show final constants
-classpath Specify where to find user class files
-cp Specify where to find user class files
-bootclasspath Override location of bootstrap class files
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-
-版本
用于打印Java的版本信息。
示例
javap -version
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输出
C:UsersAashi>javap -version
1.8.0_151
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-
-v 或 -verbose -
这用于打印附加信息，例如堆栈大小、局部变量数量和方法参数。
示例
javap -v class_name
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输出
C:UsersAashi>javap -v java.lang.Object
Classfile jar:file:/C:/Program%20Files/Java/jdk1.8.0_151/jre/lib/rt.jar! /java/lang/Object.class
Last modified Sep 5, 2017; size 1497 bytes
MD5 checksum 074ebc688a81170b8740f1158648a3c7
Compiled from "Object.java"
public class java.lang.Object
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Integer 999999
#2 - String #16 //@
#3 = String #38 //nanosecond timeout value out of range
#4 = String #42 //timeout value is negative
#5 - Utf8 ()I
#6 = Utf8 ()Ljava/lang/Object;
#7 - Utf8 ()Ljava/lang/String;
#8 = Utf8 ()V
#9 - Utf8 (I)Ljava/lang/String;
#10 - Utf8 (J)V
#11 = Utf8 (JI)V
#12 - Utf8 (Ljava/lang/Object;)Z
#13 = Utf8 (Ljava/lang/String;)V
#14 - Utf8
#15 = Utf8
#16 - Utf8 @
#17 - Utf8 Code
#18 = Utf8 Exceptions
#19 - Utf8 Line Number Table
#20 = Utf8 Signature
#21- Utf8 Source File
#22 = Utf8 StackMapTable
#23 Utf8 Append
#24 Utf8 Clone
#25 = Utf8 Equals
#26 Utf8 finalize
#27 = Utf8 getClass
#28 Utf8 getName
#29 - Utf8 hashCode
#30 = Utf8 java/lang/Class
#31 - Utf8 java/lang/CloneNotSupportedException
#32 = Utf8 java/lang/IllegalArgumentException
#33 - Utf8 Java/lang/Integer
#34 Utf8 java/lang/InterruptedException
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-
-l -
这用于打印行号和局部变量表。
示例
javap -l class_name
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输出
C:UsersAashi>javap -1 java.lang.Object
Compiled from "Object.java”
public class java.lang.Object {
public java.lang.Object();
LineNumberTable:
line 37: 0
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
LineNumberTable:
line 149: 0
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
LineNumberTable:
line 236: 0
public final native void notify();
public final native void notifyAll();
public final native void wait(long) throws Java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
LineNumberTable:
line 447: 0
line 448: 6
line 451: 16
line 452: 26
line 456: 36
line 457: 40
line 460: 44
line 461: 49
public final void wait() throws java.lang.InterruptedException;
LineNumberTable:
line 502:0
line 503: 5
protected void finalize() throws java.lang.Throwable;
}
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-
-公开
这用于仅打印公共类和成员。
示例
javap -public class_name
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输出
C:UsersAashi>javap -public java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException; public final void wait (long, int) throws java.lang.InterruptedException; public final void wait() throws java.lang.InterruptedException;
}
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-
-受保护
这用于打印受保护/公共类和成员。
示例
javap -protected class_name
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输出
C:UsersAashi>javap -protected java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait(long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
}
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-
-包
这用于打印包/受保护/公共类和成员（默认）。
示例
javap -package class_name
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输出
C:UsersAashi>javap -package java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
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-
-c
这用于打印反汇编代码。
示例
javap -c class_name
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输出
C:UsersAashi>javap -c java.lang.Object
Compiled from "Object.java"
public class java.lang.Object (public java.lang.Object();
Code:
0: return
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
Code:
0: aload e
1: aload_1
2: 1f_acmpne 9
5:iconst_1
6: goto 10
9: iconst_0
10: ireturn
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
Code:
0: new #52 //class java/lang/StringBuilder
3: dup
4: invokespecial #74 //Method java/lang/StringBuilder."": ()V
7: aload_e
8: invokevirtual #73 // Method getClass: ()Ljava/lang/Class;
11: invokevirtual #67 // Method java/lang/class.getName:()Ljava/lang/String;
14: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;) Ljava/lang/StringBuilder;
17: 1dc #2 // String @
19: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;)Ljava/lang/StringBuilder;
22: aload_e
23: invokevirtual #78 // Method hashCode: ()I
26: invokestatic #69 // Method java/lang/Integer.toHexString: (I) Ljava/lang/String;
29: invokevirtual #76 // Method java/lang/StringBuilder.append: (Ljava/lang/String;) Ljava/lang/StringBuilder;
32: invokevirtual #75 // Method java/lang/StringBuilder.toString: ()Ljava/lang/String;
35: areturn
public final native void notify();
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-
-s -
这用于打印内部类型签名。
示例
javap -s class_name
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输出
C:UsersAashi>javap -s java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
descriptor: ()V
public final native java.lang.Class getClass();
descriptor: ()Ljava/lang/class;
public native int hashCode();
descriptor: ()I
public boolean equals(java.lang.Object);
descriptor: (Ljava/lang/Object;)Z
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
descriptor:()Ljava/lang/Object;
public java.lang.String toString();
descriptor: ()Ljava/lang/String;
public final native void notify();
descriptor: ()V
public final native void notifyAll();
descriptor: ()V
public final native void wait(long) throws java.lang.InterruptedException; descriptor: (J)V
public final void wait(long, int) throws java.lang.InterruptedException; descriptor: (JI)V
public final void wait() throws java.lang.InterruptedException;
descriptor: ()V
protected void finalize() throws java.lang.Throwable;
descriptor: ()V
static {};
descriptor: ()V
}
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-
-sysinfo -
这用于打印正在处理的类的系统信息（路径、大小、日期、MD5 哈希）。
示例
javap -sysinfo class_name
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输出
C:UsersAashi>javap -sysinfo java.lang.Object
Classfile jar:file:/C:/Program%20Files/Java/jdk1.8.0_151/jre/lib/rt.jar! /java/lang/Object.class
Last modified Sep 5, 2017; size 1497 bytes
MD5 checksum 074ebc688a81170b8740f1158648a3c7
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait (long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
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-
-常量 -
这用于打印类的最终常量。
示例
javap -constants class_name
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输出
C:UsersAashi>javap -constants java.lang.Object
Compiled from "Object.java"
public class java.lang.Object {
public java.lang.Object();
public final native java.lang.Class getClass();
public native int hashCode();
public boolean equals(java.lang.Object);
protected native java.lang.Object clone() throws java.lang.CloneNotSupportedException;
public java.lang.String toString();
public final native void notify();
public final native void notifyAll();
public final native void wait (long) throws java.lang.InterruptedException;
public final void wait(long, int) throws java.lang.InterruptedException;
public final void wait() throws java.lang.InterruptedException;
protected void finalize() throws java.lang.Throwable;
static {};
}
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结论
javap 工具对于 Java 编码人员来说是一个多方面且非常强大的工具，使他们能够诊断和调试类文档、评估字段和方法以及从类文档的字节码生成清晰的代码。这个不可或缺的工具适合所有技能水平的 Java 开发人员，使他们能够轻松扩展知识并排除 Java 程序故障。对于任何有抱负的程序员来说，javap 工具都是不可替代的财产，它肯定有助于快速提高他们的编程能力。此外，其广泛的功能可以帮助编码人员完善他们的实践，为他们在构建 Java 应用程序时提供竞争优势。
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