柚子快报激活码778899分享：javap的使用
今天听的分享里在介绍String时，提到了javap，学习了好久的java，但是好像从来没有了解过这个工具。
javap是JDK提供的一个命令行工具,javap能对给定的class文件提供的字节代码进行反编译。
通过它，可以对照源代码和字节码，从而了解很多编译器内部的工作,对更深入地理解如何提高程序执行的效率等问题有极大的帮助。
使用格式
javap
常用: javap -c -v 类名
-help --help -? 输出此用法消息
-version 版本信息
-v -verbose 输出附加信息
-l 输出行号和本地变量表
-public 仅显示公共类和成员
-protected 显示受保护的/公共类和成员
-package 显示程序包/受保护的/公共类
和成员 (默认)
-p -private 显示所有类和成员
-c 对代码进行反汇编
-s 输出内部类型签名
-sysinfo 显示正在处理的类的
系统信息 (路径, 大小, 日期, MD5 散列)
-constants 显示最终常量
-classpath
-cp
-bootclasspath
新建Hello.java
public class Hello {
private Integer aa = 1;
public String ss = "sss";
public static void main(String[] args) {
System.out.println("Hello Java");
}
}
不带参数
javap Hello
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
public Hello();
public static void main(java.lang.String[]);
}
c 对代码进行反汇编
javap -c Hello
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
public Hello();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/Object."
()V
4: aload_0
5: iconst_1
6: invokestatic #2 // Method java/lang/Integer.valueOf:
(I)Ljava/lang/Integer;
9: putfield #3 // Field aa:Ljava/lang/Integer;
12: aload_0
13: ldc #4 // String sss
15: putfield #5 // Field ss:Ljava/lang/String;
18: return
public static void main(java.lang.String[]);
Code:
0: getstatic #6 // Field java/lang/System.out:Ljava/
io/PrintStream;
3: ldc #7 // String Hello Java
5: invokevirtual #8 // Method java/io/PrintStream.printl
n:(Ljava/lang/String;)V
8: return
}
输出附加信息
javap -v Hello
Classfile /D:/WWW/11/javap/Hello.class
Last modified 2019-4-23; size 602 bytes
MD5 checksum 9eb7401f16043460fa36db8275c0f7c4
Compiled from "Hello.java"
public class Hello
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #10.#23 // java/lang/Object."
#2 = Methodref #24.#25 // java/lang/Integer.valueOf:(I)Ljava/
lang/Integer;
#3 = Fieldref #9.#26 // Hello.aa:Ljava/lang/Integer;
#4 = String #27 // sss
#5 = Fieldref #9.#28 // Hello.ss:Ljava/lang/String;
#6 = Fieldref #29.#30 // java/lang/System.out:Ljava/io/Print
Stream;
#7 = String #31 // Hello Java
#8 = Methodref #32.#33 // java/io/PrintStream.println:(Ljava/
lang/String;)V
#9 = Class #34 // Hello
#10 = Class #35 // java/lang/Object
#11 = Utf8 aa
#12 = Utf8 Ljava/lang/Integer;
#13 = Utf8 ss
#14 = Utf8 Ljava/lang/String;
#15 = Utf8
#16 = Utf8 ()V
#17 = Utf8 Code
#18 = Utf8 LineNumberTable
#19 = Utf8 main
#20 = Utf8 ([Ljava/lang/String;)V
#21 = Utf8 SourceFile
#22 = Utf8 Hello.java
#23 = NameAndType #15:#16 // "
#24 = Class #36 // java/lang/Integer
#25 = NameAndType #37:#38 // valueOf:(I)Ljava/lang/Integer;
#26 = NameAndType #11:#12 // aa:Ljava/lang/Integer;
#27 = Utf8 sss
#28 = NameAndType #13:#14 // ss:Ljava/lang/String;
#29 = Class #39 // java/lang/System
#30 = NameAndType #40:#41 // out:Ljava/io/PrintStream;
#31 = Utf8 Hello Java
#32 = Class #42 // java/io/PrintStream
#33 = NameAndType #43:#44 // println:(Ljava/lang/String;)V
#34 = Utf8 Hello
#35 = Utf8 java/lang/Object
#36 = Utf8 java/lang/Integer
#37 = Utf8 valueOf
#38 = Utf8 (I)Ljava/lang/Integer;
#39 = Utf8 java/lang/System
#40 = Utf8 out
#41 = Utf8 Ljava/io/PrintStream;
#42 = Utf8 java/io/PrintStream
#43 = Utf8 println
#44 = Utf8 (Ljava/lang/String;)V
{
public java.lang.String ss;
descriptor: Ljava/lang/String;
flags: ACC_PUBLIC
public Hello();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=2, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."
":()V
4: aload_0
5: iconst_1
6: invokestatic #2 // Method java/lang/Integer.valueO
f:(I)Ljava/lang/Integer;
9: putfield #3 // Field aa:Ljava/lang/Integer;
12: aload_0
13: ldc #4 // String sss
15: putfield #5 // Field ss:Ljava/lang/String;
18: return
LineNumberTable:
line 1: 0
line 2: 4
line 3: 12
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=1, args_size=1
0: getstatic #6 // Field java/lang/System.out:Ljav
a/io/PrintStream;
3: ldc #7 // String Hello Java
5: invokevirtual #8 // Method java/io/PrintStream.prin
tln:(Ljava/lang/String;)V
8: return
LineNumberTable:
line 5: 0
line 6: 8
}
SourceFile: "Hello.java"
输出行号和本地变量表javap -l Hello
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
public Hello();
LineNumberTable:
line 1: 0
line 2: 4
line 3: 12
public static void main(java.lang.String[]);
LineNumberTable:
line 5: 0
line 6: 8
}
javap -p Hello
Compiled from "Hello.java"
public class Hello {
private java.lang.Integer aa;
public java.lang.String ss;
public Hello();
public static void main(java.lang.String[]);
}
javap -public Hello
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
public Hello();
public static void main(java.lang.String[]);
}
javap -private Hello
Compiled from "Hello.java"
public class Hello {
private java.lang.Integer aa;
public java.lang.String ss;
public Hello();
public static void main(java.lang.String[]);
}
输出内部类型签名javap -s Hello
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
descriptor: Ljava/lang/String;
public Hello();
descriptor: ()V
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
}
显示正在处理的类的javap -sysinfo Hello
Classfile /D:/WWW/11/javap/Hello.class
Last modified 2019-4-23; size 602 bytes
MD5 checksum 9eb7401f16043460fa36db8275c0f7c4
Compiled from "Hello.java"
public class Hello {
public java.lang.String ss;
public Hello();
public static void main(java.lang.String[]);
}
柚子快报激活码778899分享：javap的使用
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