java bytecode class definition

Question

currently I am working on a project that deals with byte-code analysis. I came across the code,

char[] buff = new char[1];
//some code tainting the buff   
return (new String(buff));

in the byte code I found the relevant mapping of new String(buff) to be

Ljava/lang/StringValue.cache

can anyone of you guys explain from where this cache field comes to the scenario?

it is from jdk i.6, StringValue. according to the description, "This class consists exclusively of static methods that operate on character arrays used by Strings for storing the value. "

Can anyone put a light on this? What is its purpose actually? What I think that it is mostly because of the character buffer they used which is passed to the string as an arguement. This class is not modifying the contents of the buffer, rather I think it is just a gateway to illustrate that the content of the buffer is only for initialing a string.

With what compiler? I don't see that with JDK 7.

user207421
– user207421

2013-04-15 06:22:52 +00:00
Commented Apr 15, 2013 at 6:22 — user207421
– user207421, Commented Apr 15, 2013 at 6:22
My compiler was, jdk 1.6

P basak
– P basak

2013-04-15 21:17:34 +00:00
Commented Apr 15, 2013 at 21:17 — P basak
– P basak, Commented Apr 15, 2013 at 21:17
What kind of compiler do you use? Is it gcj?

caoxudong
– caoxudong

2013-04-16 10:00:32 +00:00
Commented Apr 16, 2013 at 10:00 — caoxudong
– caoxudong, Commented Apr 16, 2013 at 10:00
I am using mac, so it might not be gcj.

P basak
– P basak

2013-04-17 19:48:17 +00:00
Commented Apr 17, 2013 at 19:48 — P basak
– P basak, Commented Apr 17, 2013 at 19:48

Antimony · Accepted Answer · 2013-04-15 12:14:24Z

2

That shouldn't really be possible. Here's what the sequence you posted looks like after compilation by a recent Javac.

iconst_1
newarray char
astore_1
new java/lang/String
dup
aload_1
invokespecial java/lang/String <init> ([C)V
areturn

Furthermore, java/lang/StringValue doesn't even exist, at least as of jre1.7.0_17. Furthermore, the presence of a period indicates it's probably one of Jasmin's merged class/method tokens in which case it's actually referring to a class in the Ljava package, whatever that's supposed to be.

There are two main possiblities - either a broken compiler or a broken disassembler. If you post the classfile here, we can at least figure out which of those is the case.

answered Apr 15, 2013 at 12:14

Antimony

39.8k13 gold badges103 silver badges115 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

user207421 · Accepted Answer · 2013-04-15 23:21:00Z

0

It is clearly a method that returns a cached String if one already exists with the same contents. Like String.intern() in fact.

answered Apr 15, 2013 at 23:21

user207421

312k45 gold badges324 silver badges493 bronze badges

Collectives™ on Stack Overflow

java bytecode class definition

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related