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
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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
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.
I have a .jar file that represents a plugin that I am trying to mess with. This is an older version of the plugin, and a newer version was written by somebody else. I have this newer version as a project.
The newer project is full of .java files, and the old plugin is full of .class files. I can import the jar as a project, but it's still all class files. The differences between the class files and the java files are not particularly large, and I would like to see the differences between them. When I do this now, however, the text comparison changes the .class file from its normal representation in the editor to a binary representation. I know that if they were the same type of file, I could select the two and hit "Compare With". How can I do this between a .class and a .java file, or how can I turn one into the other in a way that still allows me to compare the two?
What would really be best is if there were some way for me to edit the jar, by turning the .class files into .java files.
It seems like what you will need is a decompiler to convert the Java .class files (bytecode) back into their original .java source files (text). Then you could compare to the two text files. This seems like it might be useful: http://java.decompiler.free.fr
You can use SOOT (http://www.sable.mcgill.ca/soot/) to do this. Two approaches are possible:
Decompile the .class files into .java files using Dava in SOOT, and then compare the .java files.
Convert both .class and .java files into an intermediate representation called Jimple in SOOT, and compare the Jimple files.
I think the second approach is more reasonable, because:
In the first approach, some Java files are manually developed, while the others are machine generated. Doing a diff on them creates results that are difficult to read.
The Jimple representation is very close to Java source code and relatively easy to read. Reading a diff result on this unified, machine generated format is much easier. Also, if you want, you can convert all Jimple files back to Java source code (well, this is sort of the third approach...).
Because it was a plugin, I was able to import it as a plug-in project, and there was a box to include the source folder. When I checked that I got access to the .java code and was able to diff successfully.
I am trying to open Motorola BLE API library for Android. I am not too familiar with Java so I am not sure if it is even possible.
When I try to open .class file from the library with notepad++ it contains something like:
Êþº¾ and black squares.
Is there a way to open them properly?
You can use the tool javap to disassemble .class files (= compiled Java code) but that won't tell you much.
Try to find the official documentation or the source (= .java files) by googling for the class name instead.
You will need to de-compiler to read the .class files. There are various available in the market, which are open source and free. Here is one
A .class file means that the library has already been compiled into Java's version of machine code, so you won't be able to view it in notepad. There are programs for decompiling class files back into source, but you need to make sure that a) you have the rights to do so, and b) that the particular decompiler supports the class file's particular version of Java.
For more information on decompilers, see this question:
How do I decompile Java class files?
If there source code (.java files) are provided , better use those. If not, then you have to use one of the de-compiler program. But even then if the code is obfuscated , even de-compiler would not be of any use. You have to use just the API documentation for any work.
Java is a compiled language where the source is compiled into machine readable bytecode. You have to disassemble/decompile the bytecode to get it into an even semi-readable form.
Also note that the license of the library very probably forbids you from disassembling it.
If you are really using to use the api in your application then here is the way:
See the documentation of the api that is provided.
Also import the classes in with the import statement. For eg put the classes in a new folder as "api" in current folder and the import statement would be as follows:
import api.*;
Then in the application logic make use of documentation on how to access the library.
Documentation here might help: https://developer.motorola.com/docs/bluetooth-low-energy-gatt-framework-api/
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 ?