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Recompiling and running a decompiled MCP minecraft client throws a noSuchMethod error

So in the past days i've decompiled minecraft 1.12.2 using mcp to make an "own" client. I ran it from eclipse and all was working just fine. But once i exported it, added the needed JSON file and started it from the minecraft launcher, it resulted the following error:
Exception in thread "Client thread" java.lang.NoSuchMethodError: org.apache.logging.log4j.Logger.info(Ljava/lang/String;Ljava/lang/Object;)V
at net.minecraft.client.Minecraft.<init>(Minecraft.java:420)
at net.minecraft.client.main.Main.main(Main.java:115)
In my opinion that'a a bit strange, because when I ran it from eclipse that error did NOT occur.
I was thinking about adding the logger in the specific JSON file for the version but I do not know how to do it. I took the JSON file from a video where I expected my problem to be solved, made some changes, but it didn't. I also put the folder containing the logger-jar (org.apache....) in the client jar, but still no success.
Also i just decompiled 1.12.2 and recompiled it right away to see if i had messed up my code some how.
I hope someone can help.

This means at runtime you have a class that is different than what you had at compile time. You should try unzipping the jar and searching for the class file. It sounds like you need to potentially remove it and replace it with your own version.

Thanks to all who viewed an wanted to help!
Now I found an other way to use it. I wanted to export it to test
it on my server. But instead I used my account credentials to log in directly from eclipse.
:)

Error: Could not find or load main class SnakeGame.Gameplay

[screen shot of project and error message in eclipse ide][1]
i have already made and tested a snake game in java.A siple GUI development using swing.It was running pretty fine
But when i went to create a runnable jar file i found that the classes were included in the java default package.So what i did was make a new project and copy the used resources and class.But this is the error message that shows up.
As you'll can see main is already defined in the Game play class(reffer to the image) ,hence i coudlnt think of a reason why this error message would show.
I tried changing the workspace as well but in vain,and furthermore now on running the application(with warnings ofcourse) the used resourses woulnot load!
Totally in a mess!!
could the community kindly help me fix it?
if the image is not visible try this link
https://i.stack.imgur.com/NF34x.jpg

Did you remember to include a package declaration? Remember, in order to run a java program that is inside of a package, you must include a package declaration.

Error: Could not find or load main class edu.stanford.nlp.pipeline.StanfordCoreNLPServer

I am trying to run built in server by following the guide as explained here (http://stanfordnlp.github.io/CoreNLP/corenlp-server.html) but I am seeing the error as I stated in the title.
There are 2 questions asked before related with starting built-in server but they were asked before release 3.6.0.
So I am expecting the built-in server will work properly as explained in the guide.
Am I doing something wrong?
Or do I need to download the code and compile as explained in other questions ?
There is no StanfordCoreNLPServer.jar file or something like this in the full download zip file (http://stanfordnlp.github.io/CoreNLP/download.html)
I tried to create classpath definition with full path. (in windows)

Eclipse can't find source when debugging java code

I am new to Java and started with Eclipse Kepler Service Release 1. I started a small project that contains two classes, each in its own file:
MIDI_Wrap_Test - a main (program) class
MIDI_Wrap - another class (MIDI_Wrap) which is intended as a MIDI wrapper. -
Both classes are in the same directory with file names being the same as the class name (with .java added of course). Something goes wrong and I want to debug it. However, when control transfers from the main program to the MIDI_Wrap file/class I get the error message 'source not found'.
I found out that this is a quite common error. The question and answer that seem to mirror my problem perfectly is found here. I added the project to the debug source path, noticing that the correct directories were already added but to no avail.
I must be doing something wrong but am not able to find out what. Can someone help me out of this?

I solved by shutting down eclipse and reopened it. This solved me, and code can be debug with source code view.

Eclipse ClassNotFoundException

Everything works fined, but suddenly eclipse stopped execute and junit tests or even main method, when i run them using run as - > Java application, run as -> junit test
It simply throws error
Caused by: java.lang.ClassNotFoundException: package.ClassName
whene ClassName - is class from where i trying to run method main.
It affect only one of my projects ... Different workspaces works fine, other project in same workspace works fine as well.
I'm sure if i recreate current project, error will gone. But the adjustments of this project in eclipse is really hard, so i want to avoid it.
Any clue?

The ClassName is not in the Class Path, if you start from console you should use -cp parameter , if from eclipse, please add ClassName to the sources of current(start) project.

Thanks to adarshr, I was able to look at the Problems window and determine that the build was failing because it could not find a class I had written.
I had used the MS TFS plugin to create a "shelveset" and it was supposed to have removed my pending changes in the process. However, this integration with the TFS snapin and Eclipse is obviously not well implemented, since the Eclipse project still thought the file existed and was complaining that it could not be compiled.
I went and manually deleted those "files" or "non-existing files" from the Eclipse project (that I thought I had removed with the shelveset action) and the problem was solved.
Also....
Another annoying things is that the Tomcat error I was getting by trying to debug within Eclipse was like this:
SEVERE: Error configuring application listener of class
com.CompanyName.ProjectName.servlet.StartupConfigListener
java.lang.ClassNotFoundException:
com.CompanyName.ProjectName.servlet.StartupConfigListener at
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1643)
In reality, there was no problem at all with StartupConfigListener.java!! The build failed due to the OTHER problems I mentioned above, and therefore I guess this was the first class it attempted to load and failed.... because the entire project hadn't been able to compile perhaps?
(Here's to hoping my next project is using Visual Studio instead of Eclipse!)

Ok, I finally figured it out. The problem was with installed JRE in eclipse setting. I was playing around with this setting and changed installed JRE to JDK, and for some reason it broke the eclipse project.

You can also try going back to the basics. Check your command line and VM args. I've had this situation where a VM arg I was passing in was a path to a file that had a space in the path, and I had forgotten to include the full path in quotes. So e.g., if my arg looked something like
-DFILE=C:\Documents and Settings\myfile
...I'd get a java.lang.NoClassDefFoundError caused by a java.lang.ClassNotFoundException.