How to construct the constant pool?

Question

Greetings,
I seems to have a little bit of a problem.
I have a text file, generated by the javap -c <class_name> command,
i.e.:
javap -c myClass > myClass.txt
This myClass.txt is the input I've got. I do not have the myClass.class, from which it was generated.
What I wish to do, is to generate, from this text file, a leagal, runnable, class file (i.e., myClass.class).
But, I have problems understanding how to construct the constant pool array.
I have read the VM spec (java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html).
The thing is, that it does not explain how to extract the needed information from the text file.
Can someone assist?
Would appreciate,
Ohad.

Answer 1

Compiled from Hello.java
public class Hello extends java.lang.Object {
    public Hello();
    public static void main(java.lang.String[]);
Method Hello()
   0 aload_0
   1 invokespecial #6 <Method java.lang.Object()>
   4 return
Method void main(java.lang.String[])
   0 new #4 <Class java.util.Timer>
   3 dup
   4 invokespecial #7 <Method java.util.Timer()>
   7 new #2 <Class Hello$1>
  10 dup
  11 invokespecial #5 <Method Hello$1()>
  14 lconst_0
  15 lconst_1
  16 invokevirtual #8 <Method void schedule(java.util.TimerTask, long, long)>
  19 returnWell in this example, you have opcodes with arguments which are expressed as (for example) "#7 <Method java.util.Timer()>". This describes a constant pool element. I assume #7 refers to the location within the constant pool, and the text description tells you that it's an item of type method, and gives you the method name. So for all arguments expressed in this form, you'll need to reconstruct a constant pool item.