标签：des style blog class code java
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------------------
请先看上一篇：Class类文件结构浅析
上一篇讲的都是理论，下面我们亲自实践一下。
public class Test
{
private int m;
private String str;
public int func(int m,String str)
{
str += "OK";
m = 10;
return -1;
}
public static void main(String[] arg)
{
String str = "test";
int m = 20;
new Test().func(m,str);
}
}
C:\Users\Rowand jj\Desktop>javap -verbose Test
Classfile /C:/Users/Rowand jj/Desktop/Test.class
Last modified 2014-5-2; size 616 bytes
MD5 checksum cfd6b2e7d9d99dda3b84d1dbe87ce657
Compiled from "Test.java"
public class Test
SourceFile: "Test.java"
minor version: 0
major version: 51
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #11.#26 // java/lang/Object."<init>":()V
#2 = Class #27 // java/lang/StringBuilder
#3 = Methodref #2.#26 // java/lang/StringBuilder."<init>":(
)V
#4 = Methodref #2.#28 // java/lang/StringBuilder.append:(Lj
ava/lang/String;)Ljava/lang/StringBuilder;
#5 = String #29 // OK
#6 = Methodref #2.#30 // java/lang/StringBuilder.toString:(
)Ljava/lang/String;
#7 = String #31 // test
#8 = Class #32 // Test
#9 = Methodref #8.#26 // Test."<init>":()V
#10 = Methodref #8.#33 // Test.func:(ILjava/lang/String;)I
#11 = Class #34 // java/lang/Object
#12 = Utf8 m
#13 = Utf8 I
#14 = Utf8 str
#15 = Utf8 Ljava/lang/String;
#16 = Utf8 <init>
#17 = Utf8 ()V
#18 = Utf8 Code
#19 = Utf8 LineNumberTable
#20 = Utf8 func
#21 = Utf8 (ILjava/lang/String;)I
#22 = Utf8 main
#23 = Utf8 ([Ljava/lang/String;)V
#24 = Utf8 SourceFile
#25 = Utf8 Test.java
#26 = NameAndType #16:#17 // "<init>":()V
#27 = Utf8 java/lang/StringBuilder
#28 = NameAndType #35:#36 // append:(Ljava/lang/String;)Ljava/l
ang/StringBuilder;
#29 = Utf8 OK
#30 = NameAndType #37:#38 // toString:()Ljava/lang/String;
#31 = Utf8 test
#32 = Utf8 Test
#33 = NameAndType #20:#21 // func:(ILjava/lang/String;)I
#34 = Utf8 java/lang/Object
#35 = Utf8 append
#36 = Utf8 (Ljava/lang/String;)Ljava/lang/StringBuilder;
#37 = Utf8 toString
#38 = Utf8 ()Ljava/lang/String;
{
public Test();
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 int func(int, java.lang.String);
flags: ACC_PUBLIC
Code:
stack=2, locals=3, args_size=3
0: new #2 // class java/lang/StringBuilder
3: dup
4: invokespecial #3 // Method java/lang/StringBuilder.
"<init>":()V
7: aload_2
8: invokevirtual #4 // Method java/lang/StringBuilder.
append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
11: ldc #5 // String OK
13: invokevirtual #4 // Method java/lang/StringBuilder.
append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
16: invokevirtual #6 // Method java/lang/StringBuilder.
toString:()Ljava/lang/String;
19: astore_2
20: bipush 10
22: istore_1
23: iconst_m1
24: ireturn
LineNumberTable:
line 8: 0
line 9: 20
line 10: 23
public static void main(java.lang.String[]);
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=3, locals=3, args_size=1
0: ldc #7 // String test
2: astore_1
3: bipush 20
5: istore_2
6: new #8 // class Test
9: dup
10: invokespecial #9 // Method "<init>":()V
13: iload_2
14: aload_1
15: invokevirtual #10 // Method func:(ILjava/lang/String
;)I
18: pop
19: return
LineNumberTable:
line 15: 0
line 16: 3
line 17: 6
line 18: 19
}大家可能看的有点晕，不要紧，我们一步一步来分析。下面我们使用winhex打开Test.class文件：
ClassFile {
u4 magic;//魔数(0xCAFEBABE)
u2 minor_version;//次版本号
u2 major_version;//主版本号
u2 constant_pool_count;//常量池容量计数值
cp_info constant_pool[constant_pool_count-1];//常量池
u2 access_flags;//访问标志
u2 this_class;//类索引
u2 super_class;//父类索引
u2 interfaces_count;//接口计数器
u2 interfaces[interfaces_count];//接口索引集合
u2 fields_count;//字段计数器
field_info fields[fields_count];//字段表
u2 methods_count;//方法计数器
method_info methods[methods_count];//方法表
u2 attributes_count;//属性表计数器
attribute_info attributes[attributes_count];//属性表集合
}
标签：des style blog class code java
原文地址：http://blog.csdn.net/chdjj/article/details/24872179
