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Java class editor like eclipse viewer

I decompiled a Java .jar file, after editing the problem i'm having with it, its not compiling again. So, i had to opt-in to using 7-zip to just bring out the class file and, now i've used 5 different Class Editors, all can't show me the codes like i can understand...
I used CE(Classeditor.sourceforege.net), dirtyjoe, javaeditor(javaeditor.org), Jad and JD-GUi(Seems not to do its work at all)
I imported the .jar file into Eclipse as a Project Reference Library and the most painful thing is i can see all of the class codes, but i can't edit it...It won't edit. But, it can run.
What can i do to Eclipse to be able to make it allow editing the .class files attached to it.
EDIT: I want A Class Editor That Shows in Codes Format, not bytecodes.
I have the source as well in .java format.
This Example is Eclipse Class Viewer(I want same, but not only viewer).
Eclipse Class Viewer Image, I want something similar

It sounds like you want to be able to edit class files directly. The Eclipse class viewer only works because it finds (in your project folder or online) a source code version of the jar that you're viewing. It's not actually looking at the class files and decompiling them, AFAIK. So, if you can view the source in Eclipse, your best bet may be to find the source version of the jar (on your machine or on maven, possibly, if you're using maven), and then edit it and build it yourself according to that project's build instructions. How hard that is depends on the library.
As far as being able to decompile, edit, and recompile, I'm not sure. I know that decompilers are not foolproof, and I've only used them as a last-ditch, read-only tool. It seems like it should work both ways, but I wouldn't be surprised to hear it doesn't.

Why don't I see code when viewing included Jar libraries in Eclipse?

There doesn't seem to be any code there. I expected to see class declarations so I could see what the code does but instead there's some
Are they somehow precompiled? What's the difference between included Jar file and a pure code?

You are looking at .class file, which is a generated when you compile .java file. To see what the program does, you have to look into .java file. You can refer official java documentation for that.
A .jar file is packaged file with .jar extension, it contains compiled java files and their class files. This file is usually imported into projects to use the classes defined in that package.
You can use "jar xf jar-file" command in command-prompt/terminal to extract the files from jar and look into the package.

A JAR will normally contain compiled class files. It may also contain source files or there may be a separate JAR that contains the source files, but not necessarily so.
If you want to use the library in your project, then a JAR of compiled class files is what you want. If you want the source code, then you'll have to see if it is available from wherever you downloaded this from. If all you want is to see how to use the classes, then probably what you want are JavaDocs for the library you are using. This is an HTML based API documentation.

Well, this is because you haven't attached any source for the mentioned dnsns.jar. You can attach source to existing JAR files in Eclipse. Refer this SO post: Is there an easy way to attach source in Eclipse?
For this specific dnsns.jar, it is part of your JRE, and if you are not able to see its source in your IDE, then it means that the Java that you have setup in IDE lacks the source. If your installation does not have the source (src.zip), then you can get it manually as mentioned on this SO post: Where to find Java JDK Source Code?
EDIT: Alternatively, you can also use a decompiler (e.g. http://jd.benow.ca/) to reverse engineer the source from byte code, though, it may not be the exact match to the original source but you can understand the overall idea. You can add the decompiler as the default program for opening .class files in eclipse Windows > Preferences > General > Editors > File Associations. Select *.class filter and add your decompiler as the program. Though, it is not as clean as attaching the source to JAR, but may work if you don't have access to source.
EDIT2: About your question
What's the difference between included Jar file and a pure code
Eclipse can find .java files for your own code because obviously they are in your workspace. But when you add a JAR file as library, it may have the source (.java) in it or not. If the source is available, eclipse can display it by default. If not, you have to add it manually.

lambdaj installation

we have downloaded jar files for lambdaj and its dependencies which are again jar files.
we do not know how to go about it. we have copied these files in the
C:\Program Files\Java\jre6\lib\ext
have set the class path in environment variales as:
variable: classpath
path: C:\Program Files\Java\jre6\lib\ext
but we do not know how to go further. we want to run some lambdaj programs.
can anyone suggest how to run lambdaj programs?

You would run a Java program that requires lambdaj in exactly the same way you'd run any other java program with an external dependency, i.e. by invoking the java executable passing in the fully-qualified name of the Main class, or the JAR with an appropriate manifest, or by deploying it in a servlet container, etc. Additionally you should be putting the LambdaJ JAR on the classpath for this invocation, not in the lib folder for your entire JVM.
What have you tried so far and why/how is it not working? Your question at the moment is a bit analogous to "I want to use Microsoft Word to view some Word documents, how do I do this?".
Update for comment 1: You said "it's not working". That doesn't help anyone address your problem as it gives no clue what you expected to happen and what you observed, only that they were different. As for where JAR files can be stored - you can put them in any directory, so long as that directory is on the classpath (or you add it to the classpath) of the Java application that runs. The canonical place to put external dependencies is in a folder called lib below the root of your project, but the important thing is that you choose somewhere consistent and sensible.
It sounds like you don't quite grok Java and classpaths yet. If you have followed some tutorials and are still stuck, ask for help to let you understand. Adding more detail to your question, including the layout of your files, the commands you issued, and the response that came back would be useful too.

If you are using Netbeans create a project and right click on the Libraries folder within the desired project. Click Add JAR/Folder...

Export Native library to external Package in Eclipse not working. is it a Bug?

I was about to report a but to Eclipse, but I was thinking to give this a chance here first:
If I add an external package, the application cannot find the referenced native library, except in the case specified at the below:
If my workspace consists of a single project, and I import an external package 'EX_package.jar' from a folder outside of the project folder, I can assign a folder to the native library location via:
mouse over package ->
right click ->
properties ->
Native Library ->
Enter your folder.
This does not work. In runtime the application does not load the library, System.mapLibraryName(Path) also does not work.
Further more, if I create a User Library, and add the package to it and define a folder for the native library it still does not.
If it works for you then I have a major bug since it does not work on my computer I test this in any combination I could think of, including adding the path to the windows PATH parameter, and so many other ways I can't even start to remember, nothing worked, I played with this for hours and had a colleague try to assist me, but we both came up empty.
Further more, if I have a main project that is dependent on few other projects in my workspace, and they all need to use the same 'EX_package.jar' I MUST supply a HARD COPY INTO EACH OF THEM, it will ONLY (I can't stress the ONLYNESS, I got freaked out by this) work if I have a hard copy of the package in ALL of the project folders that the main project has a dependency on, and ONLY if I configure the Native path in each of them!!
This also didn't do the trick.
please tell me there is a solution to this, this drives me nuts...
Update:
if anyone wants to try this for them selfs you can try to use JMF.jar and to refer to the native dlls, or the jmf.properties file, on my XP, I refer to the dll files and I don't need the jmf.properties file.
Thanks,
Adam Zehavi.

I missed the point that Eclipse does not export the native library.
here is a solution to what I was facing: Other answer

Issue with classpath in Java project

I'm currently working on a Java project which uses Tibco rendezvous control.
I have the tibrvj.jar file on my build path. But I'm not able to see the classes which are there in the package "com.tibco.tibrv".
This package is in the jar which is on my build path.
When I try to open the class in that package , the message displayed on class editor is : "Source not found. the jar file tibrvj.jar has no source attachment".
Is there anything that could be done to set it right ?

This looks like an IDE specific message. Which IDE are you using?
The jar in your classpath only contains the java classes (bytecode) and not the source files (.java files). It looks like you are trying to open the class in your IDE/editor. Since you do not have the java files corrsponding to these classes, the editor is comlaining.
As these are Tibco specific classes, the only option is to "decompile" the classes to see the corresponding java code. Consider using a decompiler like DJ Java Decompiler

It depends on what you mean by "I'm not able to see the classes." If you mean you're getting build failures, that's possibly a matter of not actually having it properly in your build path (how are you building?) or maybe not having the right imports.
If you mean you can't see the source code, you'll need to get hold of it somehow (is Tibco open source?) and then configure your IDE so that it knows where the source is. Of course you don't need to source just to be able to build your app which uses Tibco.
If you could give more information about exactly which problem you're facing, along with what IDE you're using (if any) we could probably help more.