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Posted to bcel-user@jakarta.apache.org by maithily mundle <mu...@cs.orst.edu> on 2002/11/01 03:30:18 UTC
Adding instructions to the byte code
I am a grad student in Oregon State University. I was trying to play with
BCEL library and now I am stuck at one point, I hope you can help me
out. I was trying to add some instructions to the class file and update
the class file. I was trying to generate the simple code.
My original file looks like this
import java.io.*;
public class cl{
public static void main(String[] args){
System.out.println("Hello");
}
}
I was trying to change it to
import java.io.*;
public class cl{
public static void main(String[] args){
int i = 5;
i=i+1;
System.out.println(i);
System.out.println("Hello");
}
}
I have succeeded in doing that, I mean adding instructions, But I could
not change the constant pool, So my new class file is not executing.
Here are the constant pool entries for my code and the one that I should
have generated after updating the class file
My constant pool
(1)CONSTANT_Methodref[10](class_index = 6, name_and_type_index = 15)
(2)CONSTANT_Fieldref[9](class_index = 16, name_and_type_index = 17)
(3)CONSTANT_String[8](string_index = 18)
(4)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 20)
(5)CONSTANT_Class[7](name_index = 21)
(6)CONSTANT_Class[7](name_index = 22)
(7)CONSTANT_Utf8[1]("<init>")
(8)CONSTANT_Utf8[1]("()V")
(9)CONSTANT_Utf8[1]("Code")
(10)CONSTANT_Utf8[1]("LineNumberTable")
(11)CONSTANT_Utf8[1]("main")
(12)CONSTANT_Utf8[1]("([Ljava/lang/String;)V")
(13)CONSTANT_Utf8[1]("SourceFile")
(14)CONSTANT_Utf8[1]("cl.java")
(15)CONSTANT_NameAndType[12](name_index = 7, signature_index = 8)
(16)CONSTANT_Class[7](name_index = 23)
(17)CONSTANT_NameAndType[12](name_index = 24, signature_index = 25)
(18)CONSTANT_Utf8[1]("Hello")
(19)CONSTANT_Class[7](name_index = 26)
(20)CONSTANT_NameAndType[12](name_index = 27, signature_index = 28)
(21)CONSTANT_Utf8[1]("cl")
(22)CONSTANT_Utf8[1]("java/lang/Object")
(23)CONSTANT_Utf8[1]("java/lang/System")
(24)CONSTANT_Utf8[1]("out")
(25)CONSTANT_Utf8[1]("Ljava/io/PrintStream;")
(26)CONSTANT_Utf8[1]("java/io/PrintStream")
(27)CONSTANT_Utf8[1]("println")
(28)CONSTANT_Utf8[1]("(Ljava/lang/String;)V")
Required constant pool
1)CONSTANT_Methodref[10](class_index = 7, name_and_type_index = 16)
2)CONSTANT_Fieldref[9](class_index = 17, name_and_type_index = 18)
3)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 20)
4)CONSTANT_String[8](string_index = 21)
5)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 22)
6)CONSTANT_Class[7](name_index = 23)
7)CONSTANT_Class[7](name_index = 24)
8)CONSTANT_Utf8[1]("<init>")
9)CONSTANT_Utf8[1]("()V")
10)CONSTANT_Utf8[1]("Code")
11)CONSTANT_Utf8[1]("LineNumberTable")
12)CONSTANT_Utf8[1]("main")
13)CONSTANT_Utf8[1]("([Ljava/lang/String;)V")
14)CONSTANT_Utf8[1]("SourceFile")
15)CONSTANT_Utf8[1]("cl.java")
16)CONSTANT_NameAndType[12](name_index = 8, signature_index = 9)
17)CONSTANT_Class[7](name_index = 25)
18)CONSTANT_NameAndType[12](name_index = 26, signature_index = 27)
19)CONSTANT_Class[7](name_index = 28)
20)CONSTANT_NameAndType[12](name_index = 29, signature_index = 30)
21)CONSTANT_Utf8[1]("Hello")
22)CONSTANT_NameAndType[12](name_index = 29, signature_index = 31)
23)CONSTANT_Utf8[1]("cl")
24)CONSTANT_Utf8[1]("java/lang/Object")
25)CONSTANT_Utf8[1]("java/lang/System")
26)CONSTANT_Utf8[1]("out")
27)CONSTANT_Utf8[1]("Ljava/io/PrintStream;")
28)CONSTANT_Utf8[1]("java/io/PrintStream")
29)CONSTANT_Utf8[1]("println")
30)CONSTANT_Utf8[1]("(I)V")
31)CONSTANT_Utf8[1]("(Ljava/lang/String;)V")
Can you plase tell me how to update the constant pool to make my new class
file work?
Maithily Mundle,
CS Department,
OSU.
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Re: Adding instructions to the byte code
Posted by maithily mundle <mu...@cs.orst.edu>.
I tried using ConstantPoolGen. I could not figure out how to put new
constants in there and where exactly in the pool to put them
On Thu, 31 Oct 2002, maithily mundle wrote:
> I am a grad student in Oregon State University. I was trying to play with
> BCEL library and now I am stuck at one point, I hope you can help me
> out. I was trying to add some instructions to the class file and update
> the class file. I was trying to generate the simple code.
>
> My original file looks like this
>
> import java.io.*;
>
> public class cl{
> public static void main(String[] args){
> System.out.println("Hello");
> }
>
> }
>
> I was trying to change it to
>
> import java.io.*;
>
> public class cl{
> public static void main(String[] args){
> int i = 5;
> i=i+1;
> System.out.println(i);
> System.out.println("Hello");
> }
>
> }
>
> I have succeeded in doing that, I mean adding instructions, But I could
> not change the constant pool, So my new class file is not executing.
> Here are the constant pool entries for my code and the one that I should
> have generated after updating the class file
>
> My constant pool
>
> (1)CONSTANT_Methodref[10](class_index = 6, name_and_type_index = 15)
> (2)CONSTANT_Fieldref[9](class_index = 16, name_and_type_index = 17)
> (3)CONSTANT_String[8](string_index = 18)
> (4)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 20)
> (5)CONSTANT_Class[7](name_index = 21)
> (6)CONSTANT_Class[7](name_index = 22)
> (7)CONSTANT_Utf8[1]("<init>")
> (8)CONSTANT_Utf8[1]("()V")
> (9)CONSTANT_Utf8[1]("Code")
> (10)CONSTANT_Utf8[1]("LineNumberTable")
> (11)CONSTANT_Utf8[1]("main")
> (12)CONSTANT_Utf8[1]("([Ljava/lang/String;)V")
> (13)CONSTANT_Utf8[1]("SourceFile")
> (14)CONSTANT_Utf8[1]("cl.java")
> (15)CONSTANT_NameAndType[12](name_index = 7, signature_index = 8)
> (16)CONSTANT_Class[7](name_index = 23)
> (17)CONSTANT_NameAndType[12](name_index = 24, signature_index = 25)
> (18)CONSTANT_Utf8[1]("Hello")
> (19)CONSTANT_Class[7](name_index = 26)
> (20)CONSTANT_NameAndType[12](name_index = 27, signature_index = 28)
> (21)CONSTANT_Utf8[1]("cl")
> (22)CONSTANT_Utf8[1]("java/lang/Object")
> (23)CONSTANT_Utf8[1]("java/lang/System")
> (24)CONSTANT_Utf8[1]("out")
> (25)CONSTANT_Utf8[1]("Ljava/io/PrintStream;")
> (26)CONSTANT_Utf8[1]("java/io/PrintStream")
> (27)CONSTANT_Utf8[1]("println")
> (28)CONSTANT_Utf8[1]("(Ljava/lang/String;)V")
>
> Required constant pool
>
> 1)CONSTANT_Methodref[10](class_index = 7, name_and_type_index = 16)
> 2)CONSTANT_Fieldref[9](class_index = 17, name_and_type_index = 18)
> 3)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 20)
> 4)CONSTANT_String[8](string_index = 21)
> 5)CONSTANT_Methodref[10](class_index = 19, name_and_type_index = 22)
> 6)CONSTANT_Class[7](name_index = 23)
> 7)CONSTANT_Class[7](name_index = 24)
> 8)CONSTANT_Utf8[1]("<init>")
> 9)CONSTANT_Utf8[1]("()V")
> 10)CONSTANT_Utf8[1]("Code")
> 11)CONSTANT_Utf8[1]("LineNumberTable")
> 12)CONSTANT_Utf8[1]("main")
> 13)CONSTANT_Utf8[1]("([Ljava/lang/String;)V")
> 14)CONSTANT_Utf8[1]("SourceFile")
> 15)CONSTANT_Utf8[1]("cl.java")
> 16)CONSTANT_NameAndType[12](name_index = 8, signature_index = 9)
> 17)CONSTANT_Class[7](name_index = 25)
> 18)CONSTANT_NameAndType[12](name_index = 26, signature_index = 27)
> 19)CONSTANT_Class[7](name_index = 28)
> 20)CONSTANT_NameAndType[12](name_index = 29, signature_index = 30)
> 21)CONSTANT_Utf8[1]("Hello")
> 22)CONSTANT_NameAndType[12](name_index = 29, signature_index = 31)
> 23)CONSTANT_Utf8[1]("cl")
> 24)CONSTANT_Utf8[1]("java/lang/Object")
> 25)CONSTANT_Utf8[1]("java/lang/System")
> 26)CONSTANT_Utf8[1]("out")
> 27)CONSTANT_Utf8[1]("Ljava/io/PrintStream;")
> 28)CONSTANT_Utf8[1]("java/io/PrintStream")
> 29)CONSTANT_Utf8[1]("println")
> 30)CONSTANT_Utf8[1]("(I)V")
> 31)CONSTANT_Utf8[1]("(Ljava/lang/String;)V")
>
> Can you plase tell me how to update the constant pool to make my new class
> file work?
>
> Maithily Mundle,
> CS Department,
> OSU.
>
>
>
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