A.1 Examining Java Classfiles
已知Java會先編譯成class檔，
也就是Source Code編譯成Byte Code。
但是要看到Byte Code內的情況一般都會略過不談，
所以現在要用到只好很雞八的來看一下了。
而一般Java的JDC工具包內其實就已經有個工具可以用了，也就是 Javap。
javap -help
Usage: javap <options> <classes>
where possible options include:
-help 顯示常用指令資訊
-version 顯示目前所用JDK版本編號
-verbose / -v [檔名] 顯示[檔名]的所以class檔資訊
-l 顯示 line number 和 local variable tables 資訊
-public 顯示 public classes 和 members (其他皆不列出)
-protected 顯示 protected/public classes 和 members
-package 顯示 package/protected/public classes 和 members (default)
-p -private 顯示 Show all classes and members
-c 打開 class看ByteCode( Disassemble the code)
-s Print internal type signatures
-sysinfo Show system info of class being processed
-constants Show final constants
-classpath <path> Specify where to find user class files
-cp <path> Specify where to find user class files
-bootclasspath <path> Override location of bootstrap class files
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public class A {
public static void main(String[] args){
int a = 9;
String c = "123";
}
public void move(int a){}
public boolean move2(){ return true;}
}
-------------------------------------------------------------------------------------------------------------
-v A
Classfile /C:/Users/haha/Desktop/New folder/A.classLast modified 2016/2/19; size 377 bytes
MD5 checksum 47008851a8f4aad1f298978ae5976262
Compiled from "A.java"
public class A
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #4.#17 // java/lang/Object."<init>":()V
#2 = String #18 // 123
#3 = Class #19 // A
#4 = Class #20 // java/lang/Object
#5 = Utf8 <init>
#6 = Utf8 ()V
#7 = Utf8 Code
#8 = Utf8 LineNumberTable
#9 = Utf8 main
#10 = Utf8 ([Ljava/lang/String;)V
#11 = Utf8 move
#12 = Utf8 (I)V
#13 = Utf8 move2
#14 = Utf8 ()Z
#15 = Utf8 SourceFile
#16 = Utf8 A.java
#17 = NameAndType #5:#6 // "<init>":()V
#18 = Utf8 123
#19 = Utf8 A
#20 = Utf8 java/lang/Object
{
public A();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 1: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=3, args_size=1
0: bipush 9
2: istore_1
3: ldc #2 // String 123
5: astore_2
6: return
LineNumberTable:
line 3: 0
line 4: 3
line 5: 6
public void move(int);
descriptor: (I)V
flags: ACC_PUBLIC
Code:
stack=0, locals=2, args_size=2
0: return
LineNumberTable:
line 7: 0
public boolean move2();
descriptor: ()Z
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: iconst_1
1: ireturn
LineNumberTable:
line 9: 0
}
SourceFile: "A.java"
-------------------------------------------------------------------------------------------------------------
-l A
Compiled from "A.java"public class A {
public A();
LineNumberTable:
line 1: 0
public static void main(java.lang.String[]);
LineNumberTable:
line 3: 0
line 4: 3
line 5: 6
public void move(int);
LineNumberTable:
line 7: 0
public boolean move2();
LineNumberTable:
line 9: 0
}
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