Is this possible to convert a .class file (from .jar external library) to a .java file? I'm trying to figure out whether it is possible or not because the source of the external library is unavailable.
What are the steps I need to take to do this?
use a java decompiler like "Cavaj". It will open the class into a txt format, copy the code to a file and save as .java
Use jad. Download it from here. It works fine with classes compiled up to SDK 1.4... 1.5, if I recall correctly.
The javap command takes class-names without the .class extension. Try
javap -c ClassName
javap will however not give you the implementations of the methods in java-syntax. It will at most give it to you in JVM bytecode format.
To actually decompile (i.e., do the reverse of javac) you will have to use proper decompiler.
http://download.cnet.com/Cavaj-Java-Decompiler/3000-2213_4-10071619.html
or may be this be of some help Java Decomilers
it is Possible to convert a class file to java file without using any tools . e.g Decompiler or something else ?
Related
Was given a couple of .class files but the .java files weren't sent with and I was hoping to find a way to get the .java files using the .class files. Thanks
You can use a decompiler to do so. One of the most major ones is JD-GUI.
JD-Core is a library that reconstructs Java source code from one or more “.class” files. JD-Core may be used to recover lost source code and explore the source of Java runtime libraries. New features of Java 5, such as annotations, generics or type “enum”, are supported. JD-GUI and JD-Eclipse include JD-Core library.
EDIT (2018-02-23): It seems that JD-GUI is incapable of decompiling bytecode compatible with Java 8+ JREs. This, obviously, changes the utility of my answer.
EDIT (2018-05-24): For replacing JD-GUI, I would recommend Luyten, which can be found here. It's very similar to JD-GUI, but supports Java 8 byte code, itself being based on Procyon.
You can use any of the java decompiler utility for this. There are a couple of few good utilities available over the internet, e.g., JD decompiler, you can also look for the eclipse plugin as well for the same.
To view java content from .class files many decompilers are available.
I'm using JD compiler which is very good.
http://jd.benow.ca/
If you want it for edit/ update puropse, one way is copy + paste from decompilers. Other solutions i'm not aware of.
You can use Jadclipse which is basically a Java Decompiler. It can be used with eclipse integration..
You can use decompiler to get .java files from a jar file or a .class file
I have a jar that I want to take out a class file and add a few lines of code to it. I got class editor, but you can't actually change any code, you can change constants and that is all. I have a program that you can read the source code from a .class but you can't change anything on it. Is there a program or eclipse plugin that you can read and EDIT the source code from a .class file?
Have a look at decompilers. They'll transform the java-bytecode back to source code. One example of such a compiler would be JD: http://jd.benow.ca/
After editing the source code you would have to compile the code again and pack it in the respective .jar file.
If your file is an old enough version, you can use jasper to disassemble it into bytecode, edit the bytecode and reassemble it using jasmin. Unfortunately these tools have not been updated in some time.
They do not produce Java code; you'll have to learn Java bytecode. But it is more reliable than the so-called "decompiler" methods.
As Java .class files are in byte-code format, you cannot modify them the way you would edit a .java source file. Bytecode is a low level language closer to the machine language rather than Java itself.
If you need to modify the source, one option is to use a decompiler, e.g. JAD (Java Decompiler), to get a source file and then change it and recompile to .class using javac. Make sure you figure out which version of Java language (1.4, 5, 6, 7, 8) has been used for the original jar file.
What you need for this is a java de-compiler. This will take the bytecode out of your class file and convert it back to its source. From there you will need to recompile the .java files that the de-compiler produces.
Here are some java de-compilers that I have seen:
http://dcompiler.sourceforge.net/
http://jd.benow.ca
Suggest I have a HelloWorld.jar file, this file contains only HelloWorld.java , which is the source code of the application.
Will it be possible to run this jar file and execute the application, even though I don't have HelloWorld.class?
Yes, it can be done: See the javax.tools api. It is not easy, but it can be done....
You will likely be better off with a script that unjars the file, compiles it, and runs it.
Directly? No. java accepts only classfiles. To use source it must be compiled with javac. Nothing keeps you or a utility from compiling the source files to class files and using those, however.
I have decompiled a jar file,
and made two classes from it. After that, I tried to make a new jar file with these two class files, using this code
jar cvf AB.jar WinRegistry.class StartPageChangeApplet.class
The file created without any errors. However, when I look at the source code on Java Decompiler, it says "Internel Error", means that I couldn't make the jar file properly.
Where am I doing doing wrong ?
Please define "made two classes from it". Which java compiler (e.g. javac.exe) are you using? Did you just copy the source to a .class file without compiling maybe?
The java decompiler JAD actually displays source code, not class bytecode. Don't get confused by the title of the editor which is saying WinRegistry.class.
So you can't just save that as a .class. You need to save it as a .java and then compile it to .class using a java compiler:
javac WinRegistry.java StartPageChangeApplet.java
jar cf AB.jar WinRegistry.class StartPageChangeApplet.class
From Eclipse, you can do this way..
I've been provided some external JAR libraries for a project I'm doing. I can access the compiled code but I can't really understand it as its not in the form I'm used to seeing. Any tips on how to 'de-code' and understand what's going on?
Thanks
Search the net for Java Decompilers (e.g. JAD). What you see in a jar is Java-Classes, i.e. the result of compiling .java files.
There are decomiplers you can use them to de-compile .class to .java. We are using JD Java decompiler.
NOTE: I think De-compilation (or) modifying de-compiled code is illegal in some countries. Be aware of it.
You could use a decompiler like JAD to decompile from .class file to .java files, but in my experience its use is quite limited
Try Java Decompiler (Yet another Fast Java decompiler) : http://java.decompiler.free.fr/ .
It can decompile your compiled library.
JAD is only supported up to 1.3.
There should be a documentation and/or source jar that you can attach to your IDE, which will allow you to access the documentation.
If not, you have to decompile it.
Keep in mind that it might be ok to treat this jar as a black box.