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Java package versions - getting it right

I would like to get deeper understanding on how Java deals with different versions of Classes/Packages/etc., but couldn't find any resources or at least the best way to google for it. The problem is as follows.
Imagine we have some external package com.external.package that contains a definition of SomeInterface.
Now I write a java class MyClass that implements SomeInterface, and using com.external.package v1.0.0. Next I package a (lean) jar containing MyClass.
Now I plug this jar in another program that is looking for implementations of SomeInterface, but in it's dependencies, it is using com.external.package v2.0.0.
Is the reason I get Failed to find any class that implements SomeInterface that versions of SomeInterface don't match in the program and in the jar that contains a class extending it?
Basically the question I would like to find an answer for is what info do jars store regarding external dependencies? Does it store the exact versions of them and if they don't match at the runtime it complains? But why does it even allow running the program with references to same dependency, but different versions?

Is the reason I get Failed to find any class that implements SomeInterface that versions of SomeInterface don't match in the program and in the jar that contains a class extending it?
There is no "versioning" happening here. Simply, the error states no such class exists on the classpath. For example, you didn't put a -cp in your java command to add that extra JAR/class file.
Other reasons this could happen is that an API marks a class as deprecated in v1, then decides to remove it from v2. In which case, you best try to compile and test your code against the proper library versions before you package your own code. If you made an uber JAR, the classes should get shaded, and you probably wouldn't have missing classes.
Maven projects do have the concept of transitive, versioned dependencies, but you've not said anything about that

Seeing that the original question has found an answer already, it seems somewhat relevant to mention that Java Packages and JARs could be used for specifying package version information as discussed in the following documentation:
https://docs.oracle.com/javase/8/docs/technotes/guides/versioning/spec/versioning2.html#wp89936
Also, the Oracle Java Tutorials discuss them and further concepts around deployment of programs as JAR Files as documented here:
https://docs.oracle.com/javase/tutorial/deployment/jar/index.html

NoSuchMethodError after cleaning the project

I'm currently getting this error:
java.lang.NoSuchMethodError: org.json.JSONObject.keySet()Ljava/util/Set;
at ee.ut.cs.Parser.accessLint(Parser.java:39)
I have tried cleaning the project to no awail.
I suspect I have an error in the src/plugin/parse-htmlraw/build.xml while creating the jar file but I'm not certain. I understand that this error is because the function does not exist at runtime, but the object is created which means that the class is there, just not that function. I decompiled the .class file in created jar and it has the necessary functions.
Code is available at https://github.com/jaansusi/WCAGgrader
Q: What is wrong with the build that produces this error?
The problem is that even if I put the necessary class files in the jar I create, they are not linked correctly and the class that's called in the jar can't locate functions inside the other classes. The class object JSONObject is created but the functions inside the JSONObject class can't be found.

If you do not find the problematic version, there is a possibility you get it (especially if you are using Spring) from the following dependency -
<artifactId>android-json</artifactId>
<groupId>com.vaadin.external.google</groupId>
excluding it worked for me,
An easy way of analyzing dependencies is the maven-helper plugin in Intellij, see here

Check for the version you have used.
There might be a case where 2 different versions are being used which in turn causes this error.

To their own maven local repository com\Google\code\gson\gson, see if there are two or more version about json, will have to do is to delete the old, and remember to look at any other place in the project is introduced into the old version of the dependence, if any, change the old version of the dependence to the new version is perfectly solved this problem

JAVA creating custom .class library file from several existing ones ECLIPSE

I was using JD-GUI to get readable content of the several .class files in order to create a custom one, because many parts of the original libraries are not used (save space and performance)
So I read the code and started creating an eclipse library project in eclipse pasting them in.
soon apeared the first weird errors:
The method getLogger(Class) from the type Logger refers to the missing type Class
Implicit super constructor Object() is undefined for default constructor. Must define an explicit constructor
and so on.
Does anyone has experience in creating libraries from other libraries in eclipse? what is going wrong?
thank you.
EDIT:
it seems that several imports are not found:
error example:
The import org.w3c.dom.stylesheets cannot be resolved
how can this be, when the original libraries are working fine? I did not remove a single class. my custom library is just a merged one with 100% the same content.

Java 6 runtime not overriding class called from within .jar dependency

I have a project with different classes and packages as dependencies. Note that everything writte below occurs in one project.
I have a class that at some point runs the code getDiagramPanel().setRelationsPaintOrder(new Comparator() {.
getDiagramPanel() calls the method from DjtSheet.class, which is located in a dependency .jar-file. This method returns the DjtDiagramPanel object. I also have a DjtDiagramPanel.java file, which should override the one from the package and contains the method setRelationsPaintOrder().
In Java 7, this works fine. It correctly calls the method from the dependency, which returns the object in the format of the class which overrides the panelclass from the dependency package.
In Java 6 however, the panelclass from the dependency package is returned instead of the one from my project.
java.lang.NoSuchMethodError:
com.dlsc.djt.gantt.DjtDiagramPanel.setRelationsPaintOrder(Ljava/util/Comparator;)V
Note that this message occurs at runtime! Compiling the project gives no errors.
How can I solve this?

This problem definitely means that you have a problem in class path. I guess that the problem is that class DjtDiagramPanel is duplicate and you have 2 different veraions: one that has method setRelationsPaintOrder and second that does not have. Apparently you compile code against the "good" version and run against the "bad" one.
When this happens you can probably change the order of class loading by playing with order of dependencies in project properties of eclipse, but it will just fail later (on production). So, you should find what is the root cause of the duplication.
First find these 2 versions of the same class. Then find how the bad version arrived to your classpath. It typically happes because of 3rd party dependencies. If you are using maven you can use dependency plugin to find the root cause and disable it using tag "exclusion".

No class found exception while using json-lib in android

I am taking the input from the web, which is an Xml file and converting into a Json data using the library json-lib . I have created a user library and added the following jars into it:-
json-lib-2.3-jdk15.jar
commons-collections.jar
commons-lang.jar
commons-logging.jar
commons-beanutils.jar
ezmorph-1.0.6.jar
xom-1.1.jar
But still gives the following error:-
08-04 13:58:31.642: ERROR/dalvikvm(484): Could not find class 'net.sf.json.xml.XMLSerializer$CustomElement', referenced from method net.sf.json.xml.XMLSerializer.addNameSpaceToElement
Can anyone help me out in resolving this issue.

Either you have a sdk level / jdk level conflict. I mean dalvik can't get the byte code of the CustomElement class of your librairy as it is compiled with to recent features for your SDK like annotations for instance.
Or there is a conflicting librairy json-lib in some other of your jars or lib folders.
(the 3 first comments are not relevant, it's just the way inner classes are compiled, using a $)
Regards,
Stéphane

Since android already support json org.json a different json library may conflict. (You can download the jar here)
Try to use this library instead of an external library on android.
BTW: You can also use this library if you need on any java code (not only android)